chapter 15 populations - welcome to miss loulousis'...
TRANSCRIPT
Chapter 5
Populations and
Communities
BIOLOGY I
Loulousis
51 Populations
Population ndashgroup of organisms of same species
that live in a specific geographical area and
interbreed
Populations tend to grow because individuals
multiply by producing offspring
Eventually limited resources in an environment limit
growth
Demography ndash statistical study of all populations
Study the composition and population to predict how size
of population will change over time
Three Key Features of
Populations
1 Population density
of individuals that live in a given area
If individuals of population are few and are spaced widely
apart they may not come into contact ndash no reproduction
A population can be widely
distributed like humans
Or a population can be
confined to one area like
the Devilrsquos Head Pupfish
Stop and Think
Three Key Features of
Populations
2Geographic Distribution
The way they are arranged in a population
Three main patterns Random even clumped
Three Key Features of
Populations
3Population Growth
of individuals in a population
Can affect ability to survive
bull Small populations most likely to become extinct
bull Random disturbances (fires floods etc) endanger small
populations
bull Interbreeding ndash reduces populationrsquos fitness
Large population has better chance of survival
Population Growth
Population growth depends on
Number of births
Number of deaths
Immigration ndash movement of individuals into of a
population - Why ndash
Emmigration ndash movement of individuals out of a
population - Why -
Growth Rate
A population grows when more individuals are born
than die in a given period
Birthrate gt death rate
Population model ndash hypothetical population that attempts
to exhibit key characteristic of a real population
bull demographers can predict what might occur in a real population
bull expressed as the number of births and deaths per thousand people
per year
Modeling Population Growth
There are two models of population growth
bull Exponential growth
bull Logistic growth
Exponential Growth
- occurs when individuals in a population reproduce
at a constant rate
If a population has abundant space and food and is
protected from predators and disease then
organisms in that population will multiply and the
population size will increase
Growth Rate and Population Size
Exponential growth curve
J-shaped
The rate of population growth stays the same as a result
the population size increases steadily
There is always more births than deaths in exponential
growth
Ex ndash single bacterial cell divides consistently every 30 minuteshellip
there will be more than 1 million in 10 hours
To calculate of individuals that will be added to
the population as it grows multiply the size of the
current population (N) by the rate of growth (r)
Exponential Growth Curve
Populations do not usually grow unchecked
Limited by predators disease and the availability of
resources
Carrying capacity ndash the population size that an
environment can sustain support at a given time (K)
Logistic Growth
As resources become less available the growth
of populations slows or stops
When birthrate decreases death rate increases
or when they are the same
S-shaped curve
Resources and Population Size
As population grows limited resources decline
(eventually will be depleted) and the growth of the
population will slow
Logistic model ndash population model in which
exponential growth is limited by a density-
dependent and independent factors
Density-dependent factors (food and water)
bull Rate at which they become depleted depends on the
population density
bull Greater the density will faster factors are depleated
(and vice versa)
Density factors
Density-dependent factors- variables affected by
number of organisms in area (depends on size
of population)
Example nesting sites as adult birds increase
there not enough nesting sites so may birds do
not have young and population decreases
Density Factors
Density-independent factors ndash variables that
affect population regardless of population size
Example weather floods fires
Logistic Growth
Human Population
More than 6 billion people
Death rate has decreased in human population
due to sanitation hygiene disease control
agricultural technology
More people = more resources needed
Industrial revolution is when human population
started to accelerate rapidly exponentially
Science and technology will determine how many
people planet earth willcan support
Rapidly Growing Populations
r-strategists ndash grow exponentially when
environmental conditions allow them to reproduce
Results in temporarily large populations
bull When conditions worsen population declines
Typically have short life span
Reproduce early and have many offspring each time they
reproduce
Offspring are small mature rapidly with little or no
parental care
Ex ndash cockroaches mosquitoes insects etc
Slowing Growing Populations
k-strategists ndash population density is usually near
carrying capacity (K) of the environment
Long life span few young slow maturing process
reproduction late in life
Often provide intensive care of their young and tend to
live in stable environments
Ex ndash tigers gorillas whales (lots of endangered species)
52 Interactions in Communities
Interactions in communities revolve around the
relationships between organisms
Interactions include
Predator-prey
bull Herbivory
Symbiosis
bull Parasitism
Coevolution
Predation
- an interaction in
which one
organism
captures and
feeds on another
organism
Predator vs prey
Community Interactions
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
51 Populations
Population ndashgroup of organisms of same species
that live in a specific geographical area and
interbreed
Populations tend to grow because individuals
multiply by producing offspring
Eventually limited resources in an environment limit
growth
Demography ndash statistical study of all populations
Study the composition and population to predict how size
of population will change over time
Three Key Features of
Populations
1 Population density
of individuals that live in a given area
If individuals of population are few and are spaced widely
apart they may not come into contact ndash no reproduction
A population can be widely
distributed like humans
Or a population can be
confined to one area like
the Devilrsquos Head Pupfish
Stop and Think
Three Key Features of
Populations
2Geographic Distribution
The way they are arranged in a population
Three main patterns Random even clumped
Three Key Features of
Populations
3Population Growth
of individuals in a population
Can affect ability to survive
bull Small populations most likely to become extinct
bull Random disturbances (fires floods etc) endanger small
populations
bull Interbreeding ndash reduces populationrsquos fitness
Large population has better chance of survival
Population Growth
Population growth depends on
Number of births
Number of deaths
Immigration ndash movement of individuals into of a
population - Why ndash
Emmigration ndash movement of individuals out of a
population - Why -
Growth Rate
A population grows when more individuals are born
than die in a given period
Birthrate gt death rate
Population model ndash hypothetical population that attempts
to exhibit key characteristic of a real population
bull demographers can predict what might occur in a real population
bull expressed as the number of births and deaths per thousand people
per year
Modeling Population Growth
There are two models of population growth
bull Exponential growth
bull Logistic growth
Exponential Growth
- occurs when individuals in a population reproduce
at a constant rate
If a population has abundant space and food and is
protected from predators and disease then
organisms in that population will multiply and the
population size will increase
Growth Rate and Population Size
Exponential growth curve
J-shaped
The rate of population growth stays the same as a result
the population size increases steadily
There is always more births than deaths in exponential
growth
Ex ndash single bacterial cell divides consistently every 30 minuteshellip
there will be more than 1 million in 10 hours
To calculate of individuals that will be added to
the population as it grows multiply the size of the
current population (N) by the rate of growth (r)
Exponential Growth Curve
Populations do not usually grow unchecked
Limited by predators disease and the availability of
resources
Carrying capacity ndash the population size that an
environment can sustain support at a given time (K)
Logistic Growth
As resources become less available the growth
of populations slows or stops
When birthrate decreases death rate increases
or when they are the same
S-shaped curve
Resources and Population Size
As population grows limited resources decline
(eventually will be depleted) and the growth of the
population will slow
Logistic model ndash population model in which
exponential growth is limited by a density-
dependent and independent factors
Density-dependent factors (food and water)
bull Rate at which they become depleted depends on the
population density
bull Greater the density will faster factors are depleated
(and vice versa)
Density factors
Density-dependent factors- variables affected by
number of organisms in area (depends on size
of population)
Example nesting sites as adult birds increase
there not enough nesting sites so may birds do
not have young and population decreases
Density Factors
Density-independent factors ndash variables that
affect population regardless of population size
Example weather floods fires
Logistic Growth
Human Population
More than 6 billion people
Death rate has decreased in human population
due to sanitation hygiene disease control
agricultural technology
More people = more resources needed
Industrial revolution is when human population
started to accelerate rapidly exponentially
Science and technology will determine how many
people planet earth willcan support
Rapidly Growing Populations
r-strategists ndash grow exponentially when
environmental conditions allow them to reproduce
Results in temporarily large populations
bull When conditions worsen population declines
Typically have short life span
Reproduce early and have many offspring each time they
reproduce
Offspring are small mature rapidly with little or no
parental care
Ex ndash cockroaches mosquitoes insects etc
Slowing Growing Populations
k-strategists ndash population density is usually near
carrying capacity (K) of the environment
Long life span few young slow maturing process
reproduction late in life
Often provide intensive care of their young and tend to
live in stable environments
Ex ndash tigers gorillas whales (lots of endangered species)
52 Interactions in Communities
Interactions in communities revolve around the
relationships between organisms
Interactions include
Predator-prey
bull Herbivory
Symbiosis
bull Parasitism
Coevolution
Predation
- an interaction in
which one
organism
captures and
feeds on another
organism
Predator vs prey
Community Interactions
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Three Key Features of
Populations
1 Population density
of individuals that live in a given area
If individuals of population are few and are spaced widely
apart they may not come into contact ndash no reproduction
A population can be widely
distributed like humans
Or a population can be
confined to one area like
the Devilrsquos Head Pupfish
Stop and Think
Three Key Features of
Populations
2Geographic Distribution
The way they are arranged in a population
Three main patterns Random even clumped
Three Key Features of
Populations
3Population Growth
of individuals in a population
Can affect ability to survive
bull Small populations most likely to become extinct
bull Random disturbances (fires floods etc) endanger small
populations
bull Interbreeding ndash reduces populationrsquos fitness
Large population has better chance of survival
Population Growth
Population growth depends on
Number of births
Number of deaths
Immigration ndash movement of individuals into of a
population - Why ndash
Emmigration ndash movement of individuals out of a
population - Why -
Growth Rate
A population grows when more individuals are born
than die in a given period
Birthrate gt death rate
Population model ndash hypothetical population that attempts
to exhibit key characteristic of a real population
bull demographers can predict what might occur in a real population
bull expressed as the number of births and deaths per thousand people
per year
Modeling Population Growth
There are two models of population growth
bull Exponential growth
bull Logistic growth
Exponential Growth
- occurs when individuals in a population reproduce
at a constant rate
If a population has abundant space and food and is
protected from predators and disease then
organisms in that population will multiply and the
population size will increase
Growth Rate and Population Size
Exponential growth curve
J-shaped
The rate of population growth stays the same as a result
the population size increases steadily
There is always more births than deaths in exponential
growth
Ex ndash single bacterial cell divides consistently every 30 minuteshellip
there will be more than 1 million in 10 hours
To calculate of individuals that will be added to
the population as it grows multiply the size of the
current population (N) by the rate of growth (r)
Exponential Growth Curve
Populations do not usually grow unchecked
Limited by predators disease and the availability of
resources
Carrying capacity ndash the population size that an
environment can sustain support at a given time (K)
Logistic Growth
As resources become less available the growth
of populations slows or stops
When birthrate decreases death rate increases
or when they are the same
S-shaped curve
Resources and Population Size
As population grows limited resources decline
(eventually will be depleted) and the growth of the
population will slow
Logistic model ndash population model in which
exponential growth is limited by a density-
dependent and independent factors
Density-dependent factors (food and water)
bull Rate at which they become depleted depends on the
population density
bull Greater the density will faster factors are depleated
(and vice versa)
Density factors
Density-dependent factors- variables affected by
number of organisms in area (depends on size
of population)
Example nesting sites as adult birds increase
there not enough nesting sites so may birds do
not have young and population decreases
Density Factors
Density-independent factors ndash variables that
affect population regardless of population size
Example weather floods fires
Logistic Growth
Human Population
More than 6 billion people
Death rate has decreased in human population
due to sanitation hygiene disease control
agricultural technology
More people = more resources needed
Industrial revolution is when human population
started to accelerate rapidly exponentially
Science and technology will determine how many
people planet earth willcan support
Rapidly Growing Populations
r-strategists ndash grow exponentially when
environmental conditions allow them to reproduce
Results in temporarily large populations
bull When conditions worsen population declines
Typically have short life span
Reproduce early and have many offspring each time they
reproduce
Offspring are small mature rapidly with little or no
parental care
Ex ndash cockroaches mosquitoes insects etc
Slowing Growing Populations
k-strategists ndash population density is usually near
carrying capacity (K) of the environment
Long life span few young slow maturing process
reproduction late in life
Often provide intensive care of their young and tend to
live in stable environments
Ex ndash tigers gorillas whales (lots of endangered species)
52 Interactions in Communities
Interactions in communities revolve around the
relationships between organisms
Interactions include
Predator-prey
bull Herbivory
Symbiosis
bull Parasitism
Coevolution
Predation
- an interaction in
which one
organism
captures and
feeds on another
organism
Predator vs prey
Community Interactions
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
A population can be widely
distributed like humans
Or a population can be
confined to one area like
the Devilrsquos Head Pupfish
Stop and Think
Three Key Features of
Populations
2Geographic Distribution
The way they are arranged in a population
Three main patterns Random even clumped
Three Key Features of
Populations
3Population Growth
of individuals in a population
Can affect ability to survive
bull Small populations most likely to become extinct
bull Random disturbances (fires floods etc) endanger small
populations
bull Interbreeding ndash reduces populationrsquos fitness
Large population has better chance of survival
Population Growth
Population growth depends on
Number of births
Number of deaths
Immigration ndash movement of individuals into of a
population - Why ndash
Emmigration ndash movement of individuals out of a
population - Why -
Growth Rate
A population grows when more individuals are born
than die in a given period
Birthrate gt death rate
Population model ndash hypothetical population that attempts
to exhibit key characteristic of a real population
bull demographers can predict what might occur in a real population
bull expressed as the number of births and deaths per thousand people
per year
Modeling Population Growth
There are two models of population growth
bull Exponential growth
bull Logistic growth
Exponential Growth
- occurs when individuals in a population reproduce
at a constant rate
If a population has abundant space and food and is
protected from predators and disease then
organisms in that population will multiply and the
population size will increase
Growth Rate and Population Size
Exponential growth curve
J-shaped
The rate of population growth stays the same as a result
the population size increases steadily
There is always more births than deaths in exponential
growth
Ex ndash single bacterial cell divides consistently every 30 minuteshellip
there will be more than 1 million in 10 hours
To calculate of individuals that will be added to
the population as it grows multiply the size of the
current population (N) by the rate of growth (r)
Exponential Growth Curve
Populations do not usually grow unchecked
Limited by predators disease and the availability of
resources
Carrying capacity ndash the population size that an
environment can sustain support at a given time (K)
Logistic Growth
As resources become less available the growth
of populations slows or stops
When birthrate decreases death rate increases
or when they are the same
S-shaped curve
Resources and Population Size
As population grows limited resources decline
(eventually will be depleted) and the growth of the
population will slow
Logistic model ndash population model in which
exponential growth is limited by a density-
dependent and independent factors
Density-dependent factors (food and water)
bull Rate at which they become depleted depends on the
population density
bull Greater the density will faster factors are depleated
(and vice versa)
Density factors
Density-dependent factors- variables affected by
number of organisms in area (depends on size
of population)
Example nesting sites as adult birds increase
there not enough nesting sites so may birds do
not have young and population decreases
Density Factors
Density-independent factors ndash variables that
affect population regardless of population size
Example weather floods fires
Logistic Growth
Human Population
More than 6 billion people
Death rate has decreased in human population
due to sanitation hygiene disease control
agricultural technology
More people = more resources needed
Industrial revolution is when human population
started to accelerate rapidly exponentially
Science and technology will determine how many
people planet earth willcan support
Rapidly Growing Populations
r-strategists ndash grow exponentially when
environmental conditions allow them to reproduce
Results in temporarily large populations
bull When conditions worsen population declines
Typically have short life span
Reproduce early and have many offspring each time they
reproduce
Offspring are small mature rapidly with little or no
parental care
Ex ndash cockroaches mosquitoes insects etc
Slowing Growing Populations
k-strategists ndash population density is usually near
carrying capacity (K) of the environment
Long life span few young slow maturing process
reproduction late in life
Often provide intensive care of their young and tend to
live in stable environments
Ex ndash tigers gorillas whales (lots of endangered species)
52 Interactions in Communities
Interactions in communities revolve around the
relationships between organisms
Interactions include
Predator-prey
bull Herbivory
Symbiosis
bull Parasitism
Coevolution
Predation
- an interaction in
which one
organism
captures and
feeds on another
organism
Predator vs prey
Community Interactions
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Stop and Think
Three Key Features of
Populations
2Geographic Distribution
The way they are arranged in a population
Three main patterns Random even clumped
Three Key Features of
Populations
3Population Growth
of individuals in a population
Can affect ability to survive
bull Small populations most likely to become extinct
bull Random disturbances (fires floods etc) endanger small
populations
bull Interbreeding ndash reduces populationrsquos fitness
Large population has better chance of survival
Population Growth
Population growth depends on
Number of births
Number of deaths
Immigration ndash movement of individuals into of a
population - Why ndash
Emmigration ndash movement of individuals out of a
population - Why -
Growth Rate
A population grows when more individuals are born
than die in a given period
Birthrate gt death rate
Population model ndash hypothetical population that attempts
to exhibit key characteristic of a real population
bull demographers can predict what might occur in a real population
bull expressed as the number of births and deaths per thousand people
per year
Modeling Population Growth
There are two models of population growth
bull Exponential growth
bull Logistic growth
Exponential Growth
- occurs when individuals in a population reproduce
at a constant rate
If a population has abundant space and food and is
protected from predators and disease then
organisms in that population will multiply and the
population size will increase
Growth Rate and Population Size
Exponential growth curve
J-shaped
The rate of population growth stays the same as a result
the population size increases steadily
There is always more births than deaths in exponential
growth
Ex ndash single bacterial cell divides consistently every 30 minuteshellip
there will be more than 1 million in 10 hours
To calculate of individuals that will be added to
the population as it grows multiply the size of the
current population (N) by the rate of growth (r)
Exponential Growth Curve
Populations do not usually grow unchecked
Limited by predators disease and the availability of
resources
Carrying capacity ndash the population size that an
environment can sustain support at a given time (K)
Logistic Growth
As resources become less available the growth
of populations slows or stops
When birthrate decreases death rate increases
or when they are the same
S-shaped curve
Resources and Population Size
As population grows limited resources decline
(eventually will be depleted) and the growth of the
population will slow
Logistic model ndash population model in which
exponential growth is limited by a density-
dependent and independent factors
Density-dependent factors (food and water)
bull Rate at which they become depleted depends on the
population density
bull Greater the density will faster factors are depleated
(and vice versa)
Density factors
Density-dependent factors- variables affected by
number of organisms in area (depends on size
of population)
Example nesting sites as adult birds increase
there not enough nesting sites so may birds do
not have young and population decreases
Density Factors
Density-independent factors ndash variables that
affect population regardless of population size
Example weather floods fires
Logistic Growth
Human Population
More than 6 billion people
Death rate has decreased in human population
due to sanitation hygiene disease control
agricultural technology
More people = more resources needed
Industrial revolution is when human population
started to accelerate rapidly exponentially
Science and technology will determine how many
people planet earth willcan support
Rapidly Growing Populations
r-strategists ndash grow exponentially when
environmental conditions allow them to reproduce
Results in temporarily large populations
bull When conditions worsen population declines
Typically have short life span
Reproduce early and have many offspring each time they
reproduce
Offspring are small mature rapidly with little or no
parental care
Ex ndash cockroaches mosquitoes insects etc
Slowing Growing Populations
k-strategists ndash population density is usually near
carrying capacity (K) of the environment
Long life span few young slow maturing process
reproduction late in life
Often provide intensive care of their young and tend to
live in stable environments
Ex ndash tigers gorillas whales (lots of endangered species)
52 Interactions in Communities
Interactions in communities revolve around the
relationships between organisms
Interactions include
Predator-prey
bull Herbivory
Symbiosis
bull Parasitism
Coevolution
Predation
- an interaction in
which one
organism
captures and
feeds on another
organism
Predator vs prey
Community Interactions
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Three Key Features of
Populations
2Geographic Distribution
The way they are arranged in a population
Three main patterns Random even clumped
Three Key Features of
Populations
3Population Growth
of individuals in a population
Can affect ability to survive
bull Small populations most likely to become extinct
bull Random disturbances (fires floods etc) endanger small
populations
bull Interbreeding ndash reduces populationrsquos fitness
Large population has better chance of survival
Population Growth
Population growth depends on
Number of births
Number of deaths
Immigration ndash movement of individuals into of a
population - Why ndash
Emmigration ndash movement of individuals out of a
population - Why -
Growth Rate
A population grows when more individuals are born
than die in a given period
Birthrate gt death rate
Population model ndash hypothetical population that attempts
to exhibit key characteristic of a real population
bull demographers can predict what might occur in a real population
bull expressed as the number of births and deaths per thousand people
per year
Modeling Population Growth
There are two models of population growth
bull Exponential growth
bull Logistic growth
Exponential Growth
- occurs when individuals in a population reproduce
at a constant rate
If a population has abundant space and food and is
protected from predators and disease then
organisms in that population will multiply and the
population size will increase
Growth Rate and Population Size
Exponential growth curve
J-shaped
The rate of population growth stays the same as a result
the population size increases steadily
There is always more births than deaths in exponential
growth
Ex ndash single bacterial cell divides consistently every 30 minuteshellip
there will be more than 1 million in 10 hours
To calculate of individuals that will be added to
the population as it grows multiply the size of the
current population (N) by the rate of growth (r)
Exponential Growth Curve
Populations do not usually grow unchecked
Limited by predators disease and the availability of
resources
Carrying capacity ndash the population size that an
environment can sustain support at a given time (K)
Logistic Growth
As resources become less available the growth
of populations slows or stops
When birthrate decreases death rate increases
or when they are the same
S-shaped curve
Resources and Population Size
As population grows limited resources decline
(eventually will be depleted) and the growth of the
population will slow
Logistic model ndash population model in which
exponential growth is limited by a density-
dependent and independent factors
Density-dependent factors (food and water)
bull Rate at which they become depleted depends on the
population density
bull Greater the density will faster factors are depleated
(and vice versa)
Density factors
Density-dependent factors- variables affected by
number of organisms in area (depends on size
of population)
Example nesting sites as adult birds increase
there not enough nesting sites so may birds do
not have young and population decreases
Density Factors
Density-independent factors ndash variables that
affect population regardless of population size
Example weather floods fires
Logistic Growth
Human Population
More than 6 billion people
Death rate has decreased in human population
due to sanitation hygiene disease control
agricultural technology
More people = more resources needed
Industrial revolution is when human population
started to accelerate rapidly exponentially
Science and technology will determine how many
people planet earth willcan support
Rapidly Growing Populations
r-strategists ndash grow exponentially when
environmental conditions allow them to reproduce
Results in temporarily large populations
bull When conditions worsen population declines
Typically have short life span
Reproduce early and have many offspring each time they
reproduce
Offspring are small mature rapidly with little or no
parental care
Ex ndash cockroaches mosquitoes insects etc
Slowing Growing Populations
k-strategists ndash population density is usually near
carrying capacity (K) of the environment
Long life span few young slow maturing process
reproduction late in life
Often provide intensive care of their young and tend to
live in stable environments
Ex ndash tigers gorillas whales (lots of endangered species)
52 Interactions in Communities
Interactions in communities revolve around the
relationships between organisms
Interactions include
Predator-prey
bull Herbivory
Symbiosis
bull Parasitism
Coevolution
Predation
- an interaction in
which one
organism
captures and
feeds on another
organism
Predator vs prey
Community Interactions
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Three Key Features of
Populations
3Population Growth
of individuals in a population
Can affect ability to survive
bull Small populations most likely to become extinct
bull Random disturbances (fires floods etc) endanger small
populations
bull Interbreeding ndash reduces populationrsquos fitness
Large population has better chance of survival
Population Growth
Population growth depends on
Number of births
Number of deaths
Immigration ndash movement of individuals into of a
population - Why ndash
Emmigration ndash movement of individuals out of a
population - Why -
Growth Rate
A population grows when more individuals are born
than die in a given period
Birthrate gt death rate
Population model ndash hypothetical population that attempts
to exhibit key characteristic of a real population
bull demographers can predict what might occur in a real population
bull expressed as the number of births and deaths per thousand people
per year
Modeling Population Growth
There are two models of population growth
bull Exponential growth
bull Logistic growth
Exponential Growth
- occurs when individuals in a population reproduce
at a constant rate
If a population has abundant space and food and is
protected from predators and disease then
organisms in that population will multiply and the
population size will increase
Growth Rate and Population Size
Exponential growth curve
J-shaped
The rate of population growth stays the same as a result
the population size increases steadily
There is always more births than deaths in exponential
growth
Ex ndash single bacterial cell divides consistently every 30 minuteshellip
there will be more than 1 million in 10 hours
To calculate of individuals that will be added to
the population as it grows multiply the size of the
current population (N) by the rate of growth (r)
Exponential Growth Curve
Populations do not usually grow unchecked
Limited by predators disease and the availability of
resources
Carrying capacity ndash the population size that an
environment can sustain support at a given time (K)
Logistic Growth
As resources become less available the growth
of populations slows or stops
When birthrate decreases death rate increases
or when they are the same
S-shaped curve
Resources and Population Size
As population grows limited resources decline
(eventually will be depleted) and the growth of the
population will slow
Logistic model ndash population model in which
exponential growth is limited by a density-
dependent and independent factors
Density-dependent factors (food and water)
bull Rate at which they become depleted depends on the
population density
bull Greater the density will faster factors are depleated
(and vice versa)
Density factors
Density-dependent factors- variables affected by
number of organisms in area (depends on size
of population)
Example nesting sites as adult birds increase
there not enough nesting sites so may birds do
not have young and population decreases
Density Factors
Density-independent factors ndash variables that
affect population regardless of population size
Example weather floods fires
Logistic Growth
Human Population
More than 6 billion people
Death rate has decreased in human population
due to sanitation hygiene disease control
agricultural technology
More people = more resources needed
Industrial revolution is when human population
started to accelerate rapidly exponentially
Science and technology will determine how many
people planet earth willcan support
Rapidly Growing Populations
r-strategists ndash grow exponentially when
environmental conditions allow them to reproduce
Results in temporarily large populations
bull When conditions worsen population declines
Typically have short life span
Reproduce early and have many offspring each time they
reproduce
Offspring are small mature rapidly with little or no
parental care
Ex ndash cockroaches mosquitoes insects etc
Slowing Growing Populations
k-strategists ndash population density is usually near
carrying capacity (K) of the environment
Long life span few young slow maturing process
reproduction late in life
Often provide intensive care of their young and tend to
live in stable environments
Ex ndash tigers gorillas whales (lots of endangered species)
52 Interactions in Communities
Interactions in communities revolve around the
relationships between organisms
Interactions include
Predator-prey
bull Herbivory
Symbiosis
bull Parasitism
Coevolution
Predation
- an interaction in
which one
organism
captures and
feeds on another
organism
Predator vs prey
Community Interactions
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Population Growth
Population growth depends on
Number of births
Number of deaths
Immigration ndash movement of individuals into of a
population - Why ndash
Emmigration ndash movement of individuals out of a
population - Why -
Growth Rate
A population grows when more individuals are born
than die in a given period
Birthrate gt death rate
Population model ndash hypothetical population that attempts
to exhibit key characteristic of a real population
bull demographers can predict what might occur in a real population
bull expressed as the number of births and deaths per thousand people
per year
Modeling Population Growth
There are two models of population growth
bull Exponential growth
bull Logistic growth
Exponential Growth
- occurs when individuals in a population reproduce
at a constant rate
If a population has abundant space and food and is
protected from predators and disease then
organisms in that population will multiply and the
population size will increase
Growth Rate and Population Size
Exponential growth curve
J-shaped
The rate of population growth stays the same as a result
the population size increases steadily
There is always more births than deaths in exponential
growth
Ex ndash single bacterial cell divides consistently every 30 minuteshellip
there will be more than 1 million in 10 hours
To calculate of individuals that will be added to
the population as it grows multiply the size of the
current population (N) by the rate of growth (r)
Exponential Growth Curve
Populations do not usually grow unchecked
Limited by predators disease and the availability of
resources
Carrying capacity ndash the population size that an
environment can sustain support at a given time (K)
Logistic Growth
As resources become less available the growth
of populations slows or stops
When birthrate decreases death rate increases
or when they are the same
S-shaped curve
Resources and Population Size
As population grows limited resources decline
(eventually will be depleted) and the growth of the
population will slow
Logistic model ndash population model in which
exponential growth is limited by a density-
dependent and independent factors
Density-dependent factors (food and water)
bull Rate at which they become depleted depends on the
population density
bull Greater the density will faster factors are depleated
(and vice versa)
Density factors
Density-dependent factors- variables affected by
number of organisms in area (depends on size
of population)
Example nesting sites as adult birds increase
there not enough nesting sites so may birds do
not have young and population decreases
Density Factors
Density-independent factors ndash variables that
affect population regardless of population size
Example weather floods fires
Logistic Growth
Human Population
More than 6 billion people
Death rate has decreased in human population
due to sanitation hygiene disease control
agricultural technology
More people = more resources needed
Industrial revolution is when human population
started to accelerate rapidly exponentially
Science and technology will determine how many
people planet earth willcan support
Rapidly Growing Populations
r-strategists ndash grow exponentially when
environmental conditions allow them to reproduce
Results in temporarily large populations
bull When conditions worsen population declines
Typically have short life span
Reproduce early and have many offspring each time they
reproduce
Offspring are small mature rapidly with little or no
parental care
Ex ndash cockroaches mosquitoes insects etc
Slowing Growing Populations
k-strategists ndash population density is usually near
carrying capacity (K) of the environment
Long life span few young slow maturing process
reproduction late in life
Often provide intensive care of their young and tend to
live in stable environments
Ex ndash tigers gorillas whales (lots of endangered species)
52 Interactions in Communities
Interactions in communities revolve around the
relationships between organisms
Interactions include
Predator-prey
bull Herbivory
Symbiosis
bull Parasitism
Coevolution
Predation
- an interaction in
which one
organism
captures and
feeds on another
organism
Predator vs prey
Community Interactions
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Growth Rate
A population grows when more individuals are born
than die in a given period
Birthrate gt death rate
Population model ndash hypothetical population that attempts
to exhibit key characteristic of a real population
bull demographers can predict what might occur in a real population
bull expressed as the number of births and deaths per thousand people
per year
Modeling Population Growth
There are two models of population growth
bull Exponential growth
bull Logistic growth
Exponential Growth
- occurs when individuals in a population reproduce
at a constant rate
If a population has abundant space and food and is
protected from predators and disease then
organisms in that population will multiply and the
population size will increase
Growth Rate and Population Size
Exponential growth curve
J-shaped
The rate of population growth stays the same as a result
the population size increases steadily
There is always more births than deaths in exponential
growth
Ex ndash single bacterial cell divides consistently every 30 minuteshellip
there will be more than 1 million in 10 hours
To calculate of individuals that will be added to
the population as it grows multiply the size of the
current population (N) by the rate of growth (r)
Exponential Growth Curve
Populations do not usually grow unchecked
Limited by predators disease and the availability of
resources
Carrying capacity ndash the population size that an
environment can sustain support at a given time (K)
Logistic Growth
As resources become less available the growth
of populations slows or stops
When birthrate decreases death rate increases
or when they are the same
S-shaped curve
Resources and Population Size
As population grows limited resources decline
(eventually will be depleted) and the growth of the
population will slow
Logistic model ndash population model in which
exponential growth is limited by a density-
dependent and independent factors
Density-dependent factors (food and water)
bull Rate at which they become depleted depends on the
population density
bull Greater the density will faster factors are depleated
(and vice versa)
Density factors
Density-dependent factors- variables affected by
number of organisms in area (depends on size
of population)
Example nesting sites as adult birds increase
there not enough nesting sites so may birds do
not have young and population decreases
Density Factors
Density-independent factors ndash variables that
affect population regardless of population size
Example weather floods fires
Logistic Growth
Human Population
More than 6 billion people
Death rate has decreased in human population
due to sanitation hygiene disease control
agricultural technology
More people = more resources needed
Industrial revolution is when human population
started to accelerate rapidly exponentially
Science and technology will determine how many
people planet earth willcan support
Rapidly Growing Populations
r-strategists ndash grow exponentially when
environmental conditions allow them to reproduce
Results in temporarily large populations
bull When conditions worsen population declines
Typically have short life span
Reproduce early and have many offspring each time they
reproduce
Offspring are small mature rapidly with little or no
parental care
Ex ndash cockroaches mosquitoes insects etc
Slowing Growing Populations
k-strategists ndash population density is usually near
carrying capacity (K) of the environment
Long life span few young slow maturing process
reproduction late in life
Often provide intensive care of their young and tend to
live in stable environments
Ex ndash tigers gorillas whales (lots of endangered species)
52 Interactions in Communities
Interactions in communities revolve around the
relationships between organisms
Interactions include
Predator-prey
bull Herbivory
Symbiosis
bull Parasitism
Coevolution
Predation
- an interaction in
which one
organism
captures and
feeds on another
organism
Predator vs prey
Community Interactions
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Modeling Population Growth
There are two models of population growth
bull Exponential growth
bull Logistic growth
Exponential Growth
- occurs when individuals in a population reproduce
at a constant rate
If a population has abundant space and food and is
protected from predators and disease then
organisms in that population will multiply and the
population size will increase
Growth Rate and Population Size
Exponential growth curve
J-shaped
The rate of population growth stays the same as a result
the population size increases steadily
There is always more births than deaths in exponential
growth
Ex ndash single bacterial cell divides consistently every 30 minuteshellip
there will be more than 1 million in 10 hours
To calculate of individuals that will be added to
the population as it grows multiply the size of the
current population (N) by the rate of growth (r)
Exponential Growth Curve
Populations do not usually grow unchecked
Limited by predators disease and the availability of
resources
Carrying capacity ndash the population size that an
environment can sustain support at a given time (K)
Logistic Growth
As resources become less available the growth
of populations slows or stops
When birthrate decreases death rate increases
or when they are the same
S-shaped curve
Resources and Population Size
As population grows limited resources decline
(eventually will be depleted) and the growth of the
population will slow
Logistic model ndash population model in which
exponential growth is limited by a density-
dependent and independent factors
Density-dependent factors (food and water)
bull Rate at which they become depleted depends on the
population density
bull Greater the density will faster factors are depleated
(and vice versa)
Density factors
Density-dependent factors- variables affected by
number of organisms in area (depends on size
of population)
Example nesting sites as adult birds increase
there not enough nesting sites so may birds do
not have young and population decreases
Density Factors
Density-independent factors ndash variables that
affect population regardless of population size
Example weather floods fires
Logistic Growth
Human Population
More than 6 billion people
Death rate has decreased in human population
due to sanitation hygiene disease control
agricultural technology
More people = more resources needed
Industrial revolution is when human population
started to accelerate rapidly exponentially
Science and technology will determine how many
people planet earth willcan support
Rapidly Growing Populations
r-strategists ndash grow exponentially when
environmental conditions allow them to reproduce
Results in temporarily large populations
bull When conditions worsen population declines
Typically have short life span
Reproduce early and have many offspring each time they
reproduce
Offspring are small mature rapidly with little or no
parental care
Ex ndash cockroaches mosquitoes insects etc
Slowing Growing Populations
k-strategists ndash population density is usually near
carrying capacity (K) of the environment
Long life span few young slow maturing process
reproduction late in life
Often provide intensive care of their young and tend to
live in stable environments
Ex ndash tigers gorillas whales (lots of endangered species)
52 Interactions in Communities
Interactions in communities revolve around the
relationships between organisms
Interactions include
Predator-prey
bull Herbivory
Symbiosis
bull Parasitism
Coevolution
Predation
- an interaction in
which one
organism
captures and
feeds on another
organism
Predator vs prey
Community Interactions
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Exponential Growth
- occurs when individuals in a population reproduce
at a constant rate
If a population has abundant space and food and is
protected from predators and disease then
organisms in that population will multiply and the
population size will increase
Growth Rate and Population Size
Exponential growth curve
J-shaped
The rate of population growth stays the same as a result
the population size increases steadily
There is always more births than deaths in exponential
growth
Ex ndash single bacterial cell divides consistently every 30 minuteshellip
there will be more than 1 million in 10 hours
To calculate of individuals that will be added to
the population as it grows multiply the size of the
current population (N) by the rate of growth (r)
Exponential Growth Curve
Populations do not usually grow unchecked
Limited by predators disease and the availability of
resources
Carrying capacity ndash the population size that an
environment can sustain support at a given time (K)
Logistic Growth
As resources become less available the growth
of populations slows or stops
When birthrate decreases death rate increases
or when they are the same
S-shaped curve
Resources and Population Size
As population grows limited resources decline
(eventually will be depleted) and the growth of the
population will slow
Logistic model ndash population model in which
exponential growth is limited by a density-
dependent and independent factors
Density-dependent factors (food and water)
bull Rate at which they become depleted depends on the
population density
bull Greater the density will faster factors are depleated
(and vice versa)
Density factors
Density-dependent factors- variables affected by
number of organisms in area (depends on size
of population)
Example nesting sites as adult birds increase
there not enough nesting sites so may birds do
not have young and population decreases
Density Factors
Density-independent factors ndash variables that
affect population regardless of population size
Example weather floods fires
Logistic Growth
Human Population
More than 6 billion people
Death rate has decreased in human population
due to sanitation hygiene disease control
agricultural technology
More people = more resources needed
Industrial revolution is when human population
started to accelerate rapidly exponentially
Science and technology will determine how many
people planet earth willcan support
Rapidly Growing Populations
r-strategists ndash grow exponentially when
environmental conditions allow them to reproduce
Results in temporarily large populations
bull When conditions worsen population declines
Typically have short life span
Reproduce early and have many offspring each time they
reproduce
Offspring are small mature rapidly with little or no
parental care
Ex ndash cockroaches mosquitoes insects etc
Slowing Growing Populations
k-strategists ndash population density is usually near
carrying capacity (K) of the environment
Long life span few young slow maturing process
reproduction late in life
Often provide intensive care of their young and tend to
live in stable environments
Ex ndash tigers gorillas whales (lots of endangered species)
52 Interactions in Communities
Interactions in communities revolve around the
relationships between organisms
Interactions include
Predator-prey
bull Herbivory
Symbiosis
bull Parasitism
Coevolution
Predation
- an interaction in
which one
organism
captures and
feeds on another
organism
Predator vs prey
Community Interactions
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Growth Rate and Population Size
Exponential growth curve
J-shaped
The rate of population growth stays the same as a result
the population size increases steadily
There is always more births than deaths in exponential
growth
Ex ndash single bacterial cell divides consistently every 30 minuteshellip
there will be more than 1 million in 10 hours
To calculate of individuals that will be added to
the population as it grows multiply the size of the
current population (N) by the rate of growth (r)
Exponential Growth Curve
Populations do not usually grow unchecked
Limited by predators disease and the availability of
resources
Carrying capacity ndash the population size that an
environment can sustain support at a given time (K)
Logistic Growth
As resources become less available the growth
of populations slows or stops
When birthrate decreases death rate increases
or when they are the same
S-shaped curve
Resources and Population Size
As population grows limited resources decline
(eventually will be depleted) and the growth of the
population will slow
Logistic model ndash population model in which
exponential growth is limited by a density-
dependent and independent factors
Density-dependent factors (food and water)
bull Rate at which they become depleted depends on the
population density
bull Greater the density will faster factors are depleated
(and vice versa)
Density factors
Density-dependent factors- variables affected by
number of organisms in area (depends on size
of population)
Example nesting sites as adult birds increase
there not enough nesting sites so may birds do
not have young and population decreases
Density Factors
Density-independent factors ndash variables that
affect population regardless of population size
Example weather floods fires
Logistic Growth
Human Population
More than 6 billion people
Death rate has decreased in human population
due to sanitation hygiene disease control
agricultural technology
More people = more resources needed
Industrial revolution is when human population
started to accelerate rapidly exponentially
Science and technology will determine how many
people planet earth willcan support
Rapidly Growing Populations
r-strategists ndash grow exponentially when
environmental conditions allow them to reproduce
Results in temporarily large populations
bull When conditions worsen population declines
Typically have short life span
Reproduce early and have many offspring each time they
reproduce
Offspring are small mature rapidly with little or no
parental care
Ex ndash cockroaches mosquitoes insects etc
Slowing Growing Populations
k-strategists ndash population density is usually near
carrying capacity (K) of the environment
Long life span few young slow maturing process
reproduction late in life
Often provide intensive care of their young and tend to
live in stable environments
Ex ndash tigers gorillas whales (lots of endangered species)
52 Interactions in Communities
Interactions in communities revolve around the
relationships between organisms
Interactions include
Predator-prey
bull Herbivory
Symbiosis
bull Parasitism
Coevolution
Predation
- an interaction in
which one
organism
captures and
feeds on another
organism
Predator vs prey
Community Interactions
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Exponential Growth Curve
Populations do not usually grow unchecked
Limited by predators disease and the availability of
resources
Carrying capacity ndash the population size that an
environment can sustain support at a given time (K)
Logistic Growth
As resources become less available the growth
of populations slows or stops
When birthrate decreases death rate increases
or when they are the same
S-shaped curve
Resources and Population Size
As population grows limited resources decline
(eventually will be depleted) and the growth of the
population will slow
Logistic model ndash population model in which
exponential growth is limited by a density-
dependent and independent factors
Density-dependent factors (food and water)
bull Rate at which they become depleted depends on the
population density
bull Greater the density will faster factors are depleated
(and vice versa)
Density factors
Density-dependent factors- variables affected by
number of organisms in area (depends on size
of population)
Example nesting sites as adult birds increase
there not enough nesting sites so may birds do
not have young and population decreases
Density Factors
Density-independent factors ndash variables that
affect population regardless of population size
Example weather floods fires
Logistic Growth
Human Population
More than 6 billion people
Death rate has decreased in human population
due to sanitation hygiene disease control
agricultural technology
More people = more resources needed
Industrial revolution is when human population
started to accelerate rapidly exponentially
Science and technology will determine how many
people planet earth willcan support
Rapidly Growing Populations
r-strategists ndash grow exponentially when
environmental conditions allow them to reproduce
Results in temporarily large populations
bull When conditions worsen population declines
Typically have short life span
Reproduce early and have many offspring each time they
reproduce
Offspring are small mature rapidly with little or no
parental care
Ex ndash cockroaches mosquitoes insects etc
Slowing Growing Populations
k-strategists ndash population density is usually near
carrying capacity (K) of the environment
Long life span few young slow maturing process
reproduction late in life
Often provide intensive care of their young and tend to
live in stable environments
Ex ndash tigers gorillas whales (lots of endangered species)
52 Interactions in Communities
Interactions in communities revolve around the
relationships between organisms
Interactions include
Predator-prey
bull Herbivory
Symbiosis
bull Parasitism
Coevolution
Predation
- an interaction in
which one
organism
captures and
feeds on another
organism
Predator vs prey
Community Interactions
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Populations do not usually grow unchecked
Limited by predators disease and the availability of
resources
Carrying capacity ndash the population size that an
environment can sustain support at a given time (K)
Logistic Growth
As resources become less available the growth
of populations slows or stops
When birthrate decreases death rate increases
or when they are the same
S-shaped curve
Resources and Population Size
As population grows limited resources decline
(eventually will be depleted) and the growth of the
population will slow
Logistic model ndash population model in which
exponential growth is limited by a density-
dependent and independent factors
Density-dependent factors (food and water)
bull Rate at which they become depleted depends on the
population density
bull Greater the density will faster factors are depleated
(and vice versa)
Density factors
Density-dependent factors- variables affected by
number of organisms in area (depends on size
of population)
Example nesting sites as adult birds increase
there not enough nesting sites so may birds do
not have young and population decreases
Density Factors
Density-independent factors ndash variables that
affect population regardless of population size
Example weather floods fires
Logistic Growth
Human Population
More than 6 billion people
Death rate has decreased in human population
due to sanitation hygiene disease control
agricultural technology
More people = more resources needed
Industrial revolution is when human population
started to accelerate rapidly exponentially
Science and technology will determine how many
people planet earth willcan support
Rapidly Growing Populations
r-strategists ndash grow exponentially when
environmental conditions allow them to reproduce
Results in temporarily large populations
bull When conditions worsen population declines
Typically have short life span
Reproduce early and have many offspring each time they
reproduce
Offspring are small mature rapidly with little or no
parental care
Ex ndash cockroaches mosquitoes insects etc
Slowing Growing Populations
k-strategists ndash population density is usually near
carrying capacity (K) of the environment
Long life span few young slow maturing process
reproduction late in life
Often provide intensive care of their young and tend to
live in stable environments
Ex ndash tigers gorillas whales (lots of endangered species)
52 Interactions in Communities
Interactions in communities revolve around the
relationships between organisms
Interactions include
Predator-prey
bull Herbivory
Symbiosis
bull Parasitism
Coevolution
Predation
- an interaction in
which one
organism
captures and
feeds on another
organism
Predator vs prey
Community Interactions
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Logistic Growth
As resources become less available the growth
of populations slows or stops
When birthrate decreases death rate increases
or when they are the same
S-shaped curve
Resources and Population Size
As population grows limited resources decline
(eventually will be depleted) and the growth of the
population will slow
Logistic model ndash population model in which
exponential growth is limited by a density-
dependent and independent factors
Density-dependent factors (food and water)
bull Rate at which they become depleted depends on the
population density
bull Greater the density will faster factors are depleated
(and vice versa)
Density factors
Density-dependent factors- variables affected by
number of organisms in area (depends on size
of population)
Example nesting sites as adult birds increase
there not enough nesting sites so may birds do
not have young and population decreases
Density Factors
Density-independent factors ndash variables that
affect population regardless of population size
Example weather floods fires
Logistic Growth
Human Population
More than 6 billion people
Death rate has decreased in human population
due to sanitation hygiene disease control
agricultural technology
More people = more resources needed
Industrial revolution is when human population
started to accelerate rapidly exponentially
Science and technology will determine how many
people planet earth willcan support
Rapidly Growing Populations
r-strategists ndash grow exponentially when
environmental conditions allow them to reproduce
Results in temporarily large populations
bull When conditions worsen population declines
Typically have short life span
Reproduce early and have many offspring each time they
reproduce
Offspring are small mature rapidly with little or no
parental care
Ex ndash cockroaches mosquitoes insects etc
Slowing Growing Populations
k-strategists ndash population density is usually near
carrying capacity (K) of the environment
Long life span few young slow maturing process
reproduction late in life
Often provide intensive care of their young and tend to
live in stable environments
Ex ndash tigers gorillas whales (lots of endangered species)
52 Interactions in Communities
Interactions in communities revolve around the
relationships between organisms
Interactions include
Predator-prey
bull Herbivory
Symbiosis
bull Parasitism
Coevolution
Predation
- an interaction in
which one
organism
captures and
feeds on another
organism
Predator vs prey
Community Interactions
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Resources and Population Size
As population grows limited resources decline
(eventually will be depleted) and the growth of the
population will slow
Logistic model ndash population model in which
exponential growth is limited by a density-
dependent and independent factors
Density-dependent factors (food and water)
bull Rate at which they become depleted depends on the
population density
bull Greater the density will faster factors are depleated
(and vice versa)
Density factors
Density-dependent factors- variables affected by
number of organisms in area (depends on size
of population)
Example nesting sites as adult birds increase
there not enough nesting sites so may birds do
not have young and population decreases
Density Factors
Density-independent factors ndash variables that
affect population regardless of population size
Example weather floods fires
Logistic Growth
Human Population
More than 6 billion people
Death rate has decreased in human population
due to sanitation hygiene disease control
agricultural technology
More people = more resources needed
Industrial revolution is when human population
started to accelerate rapidly exponentially
Science and technology will determine how many
people planet earth willcan support
Rapidly Growing Populations
r-strategists ndash grow exponentially when
environmental conditions allow them to reproduce
Results in temporarily large populations
bull When conditions worsen population declines
Typically have short life span
Reproduce early and have many offspring each time they
reproduce
Offspring are small mature rapidly with little or no
parental care
Ex ndash cockroaches mosquitoes insects etc
Slowing Growing Populations
k-strategists ndash population density is usually near
carrying capacity (K) of the environment
Long life span few young slow maturing process
reproduction late in life
Often provide intensive care of their young and tend to
live in stable environments
Ex ndash tigers gorillas whales (lots of endangered species)
52 Interactions in Communities
Interactions in communities revolve around the
relationships between organisms
Interactions include
Predator-prey
bull Herbivory
Symbiosis
bull Parasitism
Coevolution
Predation
- an interaction in
which one
organism
captures and
feeds on another
organism
Predator vs prey
Community Interactions
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Density factors
Density-dependent factors- variables affected by
number of organisms in area (depends on size
of population)
Example nesting sites as adult birds increase
there not enough nesting sites so may birds do
not have young and population decreases
Density Factors
Density-independent factors ndash variables that
affect population regardless of population size
Example weather floods fires
Logistic Growth
Human Population
More than 6 billion people
Death rate has decreased in human population
due to sanitation hygiene disease control
agricultural technology
More people = more resources needed
Industrial revolution is when human population
started to accelerate rapidly exponentially
Science and technology will determine how many
people planet earth willcan support
Rapidly Growing Populations
r-strategists ndash grow exponentially when
environmental conditions allow them to reproduce
Results in temporarily large populations
bull When conditions worsen population declines
Typically have short life span
Reproduce early and have many offspring each time they
reproduce
Offspring are small mature rapidly with little or no
parental care
Ex ndash cockroaches mosquitoes insects etc
Slowing Growing Populations
k-strategists ndash population density is usually near
carrying capacity (K) of the environment
Long life span few young slow maturing process
reproduction late in life
Often provide intensive care of their young and tend to
live in stable environments
Ex ndash tigers gorillas whales (lots of endangered species)
52 Interactions in Communities
Interactions in communities revolve around the
relationships between organisms
Interactions include
Predator-prey
bull Herbivory
Symbiosis
bull Parasitism
Coevolution
Predation
- an interaction in
which one
organism
captures and
feeds on another
organism
Predator vs prey
Community Interactions
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Density Factors
Density-independent factors ndash variables that
affect population regardless of population size
Example weather floods fires
Logistic Growth
Human Population
More than 6 billion people
Death rate has decreased in human population
due to sanitation hygiene disease control
agricultural technology
More people = more resources needed
Industrial revolution is when human population
started to accelerate rapidly exponentially
Science and technology will determine how many
people planet earth willcan support
Rapidly Growing Populations
r-strategists ndash grow exponentially when
environmental conditions allow them to reproduce
Results in temporarily large populations
bull When conditions worsen population declines
Typically have short life span
Reproduce early and have many offspring each time they
reproduce
Offspring are small mature rapidly with little or no
parental care
Ex ndash cockroaches mosquitoes insects etc
Slowing Growing Populations
k-strategists ndash population density is usually near
carrying capacity (K) of the environment
Long life span few young slow maturing process
reproduction late in life
Often provide intensive care of their young and tend to
live in stable environments
Ex ndash tigers gorillas whales (lots of endangered species)
52 Interactions in Communities
Interactions in communities revolve around the
relationships between organisms
Interactions include
Predator-prey
bull Herbivory
Symbiosis
bull Parasitism
Coevolution
Predation
- an interaction in
which one
organism
captures and
feeds on another
organism
Predator vs prey
Community Interactions
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Logistic Growth
Human Population
More than 6 billion people
Death rate has decreased in human population
due to sanitation hygiene disease control
agricultural technology
More people = more resources needed
Industrial revolution is when human population
started to accelerate rapidly exponentially
Science and technology will determine how many
people planet earth willcan support
Rapidly Growing Populations
r-strategists ndash grow exponentially when
environmental conditions allow them to reproduce
Results in temporarily large populations
bull When conditions worsen population declines
Typically have short life span
Reproduce early and have many offspring each time they
reproduce
Offspring are small mature rapidly with little or no
parental care
Ex ndash cockroaches mosquitoes insects etc
Slowing Growing Populations
k-strategists ndash population density is usually near
carrying capacity (K) of the environment
Long life span few young slow maturing process
reproduction late in life
Often provide intensive care of their young and tend to
live in stable environments
Ex ndash tigers gorillas whales (lots of endangered species)
52 Interactions in Communities
Interactions in communities revolve around the
relationships between organisms
Interactions include
Predator-prey
bull Herbivory
Symbiosis
bull Parasitism
Coevolution
Predation
- an interaction in
which one
organism
captures and
feeds on another
organism
Predator vs prey
Community Interactions
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Human Population
More than 6 billion people
Death rate has decreased in human population
due to sanitation hygiene disease control
agricultural technology
More people = more resources needed
Industrial revolution is when human population
started to accelerate rapidly exponentially
Science and technology will determine how many
people planet earth willcan support
Rapidly Growing Populations
r-strategists ndash grow exponentially when
environmental conditions allow them to reproduce
Results in temporarily large populations
bull When conditions worsen population declines
Typically have short life span
Reproduce early and have many offspring each time they
reproduce
Offspring are small mature rapidly with little or no
parental care
Ex ndash cockroaches mosquitoes insects etc
Slowing Growing Populations
k-strategists ndash population density is usually near
carrying capacity (K) of the environment
Long life span few young slow maturing process
reproduction late in life
Often provide intensive care of their young and tend to
live in stable environments
Ex ndash tigers gorillas whales (lots of endangered species)
52 Interactions in Communities
Interactions in communities revolve around the
relationships between organisms
Interactions include
Predator-prey
bull Herbivory
Symbiosis
bull Parasitism
Coevolution
Predation
- an interaction in
which one
organism
captures and
feeds on another
organism
Predator vs prey
Community Interactions
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Rapidly Growing Populations
r-strategists ndash grow exponentially when
environmental conditions allow them to reproduce
Results in temporarily large populations
bull When conditions worsen population declines
Typically have short life span
Reproduce early and have many offspring each time they
reproduce
Offspring are small mature rapidly with little or no
parental care
Ex ndash cockroaches mosquitoes insects etc
Slowing Growing Populations
k-strategists ndash population density is usually near
carrying capacity (K) of the environment
Long life span few young slow maturing process
reproduction late in life
Often provide intensive care of their young and tend to
live in stable environments
Ex ndash tigers gorillas whales (lots of endangered species)
52 Interactions in Communities
Interactions in communities revolve around the
relationships between organisms
Interactions include
Predator-prey
bull Herbivory
Symbiosis
bull Parasitism
Coevolution
Predation
- an interaction in
which one
organism
captures and
feeds on another
organism
Predator vs prey
Community Interactions
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Slowing Growing Populations
k-strategists ndash population density is usually near
carrying capacity (K) of the environment
Long life span few young slow maturing process
reproduction late in life
Often provide intensive care of their young and tend to
live in stable environments
Ex ndash tigers gorillas whales (lots of endangered species)
52 Interactions in Communities
Interactions in communities revolve around the
relationships between organisms
Interactions include
Predator-prey
bull Herbivory
Symbiosis
bull Parasitism
Coevolution
Predation
- an interaction in
which one
organism
captures and
feeds on another
organism
Predator vs prey
Community Interactions
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
52 Interactions in Communities
Interactions in communities revolve around the
relationships between organisms
Interactions include
Predator-prey
bull Herbivory
Symbiosis
bull Parasitism
Coevolution
Predation
- an interaction in
which one
organism
captures and
feeds on another
organism
Predator vs prey
Community Interactions
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Predation
- an interaction in
which one
organism
captures and
feeds on another
organism
Predator vs prey
Community Interactions
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Predation
Come in all different sizes even microscopic
Most animals are both predators and prey
Few species are not hunted by others
Killer whales are not hunted by any other animals
Coevolution ndash evolution of 2 or more species due
to mutual influence
Predator-prey or parasite-host relations often develop
adaptations in response to one another
bull Prey evolve to be faster runners
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Herbivory
Herbivores do not usually kill the plants they eat
Plants develop methods of defense against
herbivores
Horns or spines cause pain when eating
Chemical compounds that taste bad or make ill
Herbivores evolved ways to overcome plant defenses
bull Monarch butterfly caterpillars feed on milkweed
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Symbiosis - means ldquoliving togetherrdquo
Biologists recognize three main
typeshellip
Community Interactions
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
1 Mutualism ndash
both species benefit
example
bees and flowers
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
2 Commensalism ndash
one member benefits the other
is neither helped nor harmed
Example barnacles and whales
Orchids and trees
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Parasitism
Relationship in which one species benefits and the
other is harmed
Parasites feed on host which is usually larger and
harm it but often do not kill the host
Example tapeworms
Live in digestive system
of host
Fleas live on skin
3 Parasitism
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
1 Explain how predator-prey
interactions influence both predators
and prey
2 Define symbiosis
3 Mites live at the base of human
eyelashes They eat the dead skin and
other detritus there What type of
relationship do mites have with
humans
Stop and Think
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
The interactions among organisms
in communities shape the
ecosystem and the organisms that
live there
53 Shaping Communities
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Niche
A species physical use (of space) of its habitat and
its function within a community
Different from habitat- place organisms lives
Think of habitat as the organismrsquos ecological address
Think of its niche as its profession or job what it does to
survive
An organismrsquos habitat is part of its niche
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
1 Fundamental Niche ldquothe
potentialrdquo
Largest niche where an organism or species can live
without competition
bull Includes all the places could nest and eat
Often shared with other species which leads to
fundamental niches overlapping between species
No two species want to be in direct competition with each
other so they will divide up the resources and reduce
their fundamental niche size
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
2 Realized Niche ldquothe realisticrdquo
So species use only part of their fundamental niche which
becomes itrsquos realized niche
Realized Niche- Actual niche includes its range of
resources for use the conditions it tolerates and its
functionality in the ecosystem
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Competition
competition arises when two or more individuals
(or populations) rely on the same limited resource
In doing so both parties are impacted negatively
Stealing of food is called kleptoparasitism
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Competitive Exclusion
When one species eliminates another through
competition
Similar species have similar needs leads to competition
The organism that is slightly better at getting the resource
will survive and reproduce successfully
The other either dies or moves to new ecosystem
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Dividing Resources
However some competitors do still live in the same place
This is possible because they divide the resources by possibly feeding in slightly different ways or in slightly different places
Example Warbler
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Ecosystem Resiliency
Resilience ability to recover or adjust easily to
change or misfortune without major affects
Ecosystems are destroyed or damaged by severe
weather humans or introduced species
Two factors that affect an ecosystemrsquos resiliency
Predation
Biodiversity
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Predation and Resiliency
Predation reduces effects of competition
Predators influence more than their prey
Some predators are keystone species species that is
critical to an ecosystem due to its affects on the survival
and number of many other organisms in the community
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Keystone species
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Biodiversity and Resiliency
Communities with greater number of different
species can recover quicker from a major
disturbance like a drought
The diversity allows the ecosystem to recover
easily
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
1 How is a niche different from a
habitat
2 One competing species
eliminating another through
competition is called
Stop and Think
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
End of chapter 5
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
52 How Populations Evolve
The change of population allele frequencies
From genetics we now have a better
understanding of how natural selection occurs
+ how it changes the proportions of alleles within
populations
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Allele Frequencies
Hardy-Weinberg principle ndash states that the
frequencies of alleles in a population do not
change unless evolutionary forces act on the
population
They used to think dominant alleles would spontaneously
replace recessive alleles within populations
Using a simple algebra equation they showed that the
frequency of alleles in a population does not change from
generation to generation unless the population is acted
on by processes that favor particular genes
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Hardy-Weinberg Principle
Holds true for any population as long as the
population is large enough that its members are
not likely to mate with relatives and as long as
evolutionary forces are not acting
There are 5 principle evolutionary forces
Mutation
Gene flow
Nonrandom mating
Genetic drift
Natural selection
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Mutation
Mutations rates are very low in nature
Most genes mutate about 1 to 10 times per 100000 cell
divisions
Does not significantly change allele frequencies
except over very long periods of time
Not all mutations result in phenotypic changes
Recall that more than one codon can code for the same amino
acid
bull Some mutations may result in no change in the amino acid coded for in
a protein
bull Or it could mutate and affect the way the protein works
Is the source of variation and makes evolution possible
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Gene Flow
Movement of individuals to or from a population
called migration creates gene flow
Gene flow = movement of alleles into or out of a
population
Immigrants add alleles to the population and
departing emigrants take alleles away
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Nonrandom Mating
When individuals prefer to mate with others that
live nearby or are of their own phenotype
Inbreeding is also a type of nonrandom mating
bull Causes a lower frequency of heterozygotes
bull Does not change frequency of alleles but it does increase proportion of
homozygotes in a population
Also occurs when organisms choose their mates
based on certain traits
In animals females often choose their males based in
their size color ability to gather food or others
httpwwwyoutubecomwatchv=nS1tEnfkk6M
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Genetic Drift
Frequency of allele can be greatly changed by a
chance event
Fire or landslide when only a few survive
Appears randomly as if the frequency were drifting so it
is called genetic drifting
Also occurs in small isolated populations
Cheetahs ndash undergone drastic population declines
As a result almost all cheetahs alive together are almost
genetically identical
bull Consequence = reduced disease resistance etc
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Natural Selection
Causes deviations from the Hardy-Weinberg
proportions
Directly changes the frequencies of alleles
Frequency of allele will increase or decrease depending
on the allelersquos effect on survival and reproduction
ie ndash allele for sickle cell anemia slowly declining
bull Individuals who are homozygous for this allele rarely have children
Natural selection = one of the most powerful
agents of genetic change
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Action on Natural Selection of
Phenotypes
Constantly changes populations through actions
on individuals within the population
Does not act directly on genes
bull Enables individuals who express favorable traits to reproduce and
pass those traits on to their offspring
bull Natural selection acts on phenotypes not genotypes
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
How Selection Acts
Only characteristics that are expressed can be
targets of natural selection
Selection cannot operate against rare recessive alleles
even if they are unfavorable
Only when the allele becomes common enough that
heterozygous individuals come together and produce
homozygous offspring does natural selection have the
opportunity to act
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Why Genes Persist
A recessive allele (a) is homozygous in only 1 out of 100 individuals then 18 out of 100 will be heterozygous (Aa) and will carry the allele unexpressed Natural selection can only act on every 1 in 19 individuals
bull This leaves 18 that maintain the allele in the population
Cystic fibrosis ndash most common fatal disorder amount Caucasians 1 in 25 have a copy of the defective gene and show no
symptoms
bull Homozygous recessive individuals are about 1 in 2500 and die from the disease
bull Genetic conditions are not eliminated because very few of the individuals bearing the alleles express the recessive phenotype
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Natural Selection and the
Distribution of Traits
Natural selection shapes populations affected by phenotypes that are controlled by one or by a large number of genes
A trait that is influenced by several genes is called a polygenic trait
Polygenic traits tend to exhibit a range of phenotypes clustered around an average value If you were to plot the height of everyone in your class on a graph the values would probably form a hill-shaped curve called a normal distribution
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Normal Distribution
This hill-shaped curve
represents a normal
distribution
The blue dashed line
represents the average
height for this
population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Directional Selection
When selection eliminates one extreme from a range of phenotypes the alleles promoting this extreme become less common in the population
In directional selection the frequency of a particular trait moves in one direction in a range
Directional selection has a role in the evolution of single-gene traits such as pesticide resistance in insects
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Stabilizing Selection
When selection reduces extremes in a range of phenotypes the frequencies of the intermediate phenotypes increase
As a result the population contains fewer individuals that have alleles promoting extreme types
In stabilizing selection the distribution becomes narrower tending to ldquostabilizerdquo the average by increasing the proportion of similar individuals
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population
Directional selection is the change on the average
value of a population
Stabilizing selection is the increase of the number
of average individuals in a population