ecosystems and living organisms · ecosystems and living organisms. chapter overview i. evolution...
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Ecosystems and Living Organisms
Chapter Overview
I. Evolution
II. Succession
III. Keystone Species
IV. Symbiosis
V. Predation
VI. Competition
VII. Species Richness
The American Alligator
Diversity of Life
Kingdoms of Life
Diversity of Life
Species
Similar organisms
that have the
potential to
produce viable
offspring together.
Evolution
• Genetic changes in a population through time.
• Mechanism for how species changed was explained by Charles Darwin.
– Origin of Species, 1859
– Evolution occurs through natural selection.
• Inherited, favorable traits are “preserved”
• Inherited, UNfavorable traits are “eliminated”
• Adaptation - genetic traits that increases the chances of survival and reproductive success.
Evolution
Survival of the Fittest
species heritable traits most suitable for the
environment are most successful.
fitness – describes the success of an organism at
surviving and reproducing.
The number of fit individuals will increase in the
population, changing the frequency of favorable
traits in the population.
Evolution
• How does evolution cause a species to change
over time?
Overproduction
Variation
Struggle for existence
Differential reproductive success
Causes
allele
frequencies
to change
(=species
change)
Evolution
Evolution• Hardy-Weinberg Equilibrium
• Allele and gene frequencies do NOT change in an ideal population.
• Population must experience the following for HW to apply:
• No mutation
• No selection
• No migration
• No genetic drift
• Random mating
• Population will not evolve if the above factors are true.
Evolution
• Hardy-Weinberg Equilibrium
• Formula:
p2 + 2pq + q2 = 1
• p = frequency of dominant allele
• q = frequency of recessive allele
• The sum of these frequencies is 1 if the population is in
equilibrium.
Evolution
3 Types:
Modes of Action
Natural selection has three modes of action:
1. Stabilizing selection
2. Directional selection
3. Diversifying selection
Number
of
Individuals
Size of individuals
Small Large
1. Stabilizing Selection
Acts upon extremes and
favors the intermediate
Number
of
Individuals
Size of individuals
Small Large
2. Directional
SelectionFavors variants of one
extreme
Number
of
Individuals
Size of individuals
Small Large
3. Diversifying
SelectionFavors variants of opposite
extremes
Number
of
Individuals
Size of individuals
Small Large
Coevolution
CoevolutionOne species acts as a selective force on a
second species Induces adaptations
Example:1. Wolf and Moose2. Acacia ants and Acacia trees3. Lichen
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Speciation
Evolution of new species
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At any given moment (e.g. the
‘present’), all we see is current
diversity…
all extinct forms are gone
(99.9%)
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BiodiversityBiodiversity increases with speciation decreases with extinction
Extinction creates evolutionary opportunities for surviving species
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Richness (number of species)
Relative abundance
Due to:
Evolutionary
history
Climate
Comparison of
Two Communities
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The larger the
geographic
area, the
greater
the number
of species
Species-Area Curve
Fig. 23.25 North American Birds
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Species Richness on Islands
Depends on:
Rate of immigration to island
Rate of extinction on island
These in turn depend on:
Island size
Distance from mainland
Species Richness
Species richness - Number of different species in a
community
Species Richness
Forest Grassland
EC
OT
ON
E
Where edge effect occurs - different
species composition
Typically greater species richness
Ecotone - transition zone where 2+ communities meet
Species Richness
Species Richness and Ecosystem Services
Ecosystem Ecosystem services
Forests,
Grasslands
Purify air / water
Produce / maintain soil
Absorb CO2
Wildlife habitat
Freshwater
systemsModerate water flow
Mitigate flooding
Dilute / remove pollutants
Drinking water
Recreation
Species Richness
Species Richness and Community Stability
Greater the richness = Greater the stability
- community stability
- ability of a community to withstand environmental
disturbance
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Threats to Ecosystem Stability
1. Drop in Primary Productivity
2. Increased Nutrient Losses
3. Decline or extinction of indicator species
4. Increased populations of insect pests or disease organisms
5. Decline in Species diversity
6. Presence of Contaminants
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How do species move? Humans (accidental and intended)
Animals (sticky seeds and scat)
Wind and ocean currents (+ or -)
Land bridges
Stepping stone islands affected by climactic changes (glaciation)
ocean levels
short-term weather patterns
Biological Communities
Rotting Log Community
Keystone Species
• Single species that strongly influences an entire
community.
• Example: figs
frugivores depend upon fruit
usually avoid figs, but during certain times of the year,
figs are only species bearing fruit
if figs were eliminated, many frugivores would die out
Interactions Among
Organisms Symbiosis –
one species living in or on another species
results from coevolution
Symbiosis
1) Mutualism - both partners benefit
Without mycorrhizae With mycorrhizae
Symbiosis
2) Commensalism - one partner benefits
and the other partner is neither harmed
nor helped.
Epiphytes
Symbiosis
3) Parasitism - one partner benefits
and the other partner is harmed
Tracheal mites
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Predator Adaptations Prey detection and recognition
sensory adaptations - distinguish prey
from non-prey
Discuss why each of the following demonstrates
sensory adaptations.
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Predator Adaptations Prey detection and recognition
sensory adaptations - distinguish prey from non-prey
Prey capture
passive vs. active
individuals vs. cooperative
Determine if the following pictures are examples of passive or
active prey capture. Explain why.
Determine if the following pictures are examples of individual or
cooperative prey capture. Explain why.
Discuss the costs and benefits of each strategy.
.
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Predator Adaptations Prey detection and recognition
sensory adaptations - distinguish prey from non-prey
Prey capture
passive vs. active
individuals vs. cooperative
Determine if the following pictures are examples of passive or
active prey capture. Explain why.
Determine if the following pictures are examples of individual or
cooperative prey capture. Explain why.
Discuss the costs and benefits of each strategy.
.
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Predator Adaptations Prey detection and recognition
sensory adaptations - distinguish prey from non-prey
Prey capture
passive vs. active
individuals vs. cooperative
Eating prey
teeth, claws etc.
Describe why each of the following is an adaptation.
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Prey AdaptationsAvoid detection
camouflage, mimics,
diurnal/nocturnal
Explain how natural selection leads to
camouflage and mimicry.
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Prey AdaptationsAvoid detection
camouflage, mimics, warning coloration
diurnal/nocturnal
Avoid capture
Flee, resist, escape
Describe how each of the following examples
demonstrates avoidance of capture.
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Prey Adaptations Avoid detection
camouflage, mimics,
diurnal/nocturnal
Avoid capture
flee
resist
escape
Disrupt handling (prevent being eaten)
struggle?
protection, toxins
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HerbivoryHerbivore needs to find most nutritious food sources.
circumvent plant defenses
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HerbivoryHerbivore needs to find most nutritious
circumvent plant defenses
Herbivory is a strong selective pressure on plants
structural adaptations for defense
chemical adaptations for defense
Explain why the following exemplifies coevolution.
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Predator-Prey Interactions Predator and prey populations are
interdependent.
Interactions Among
Organisms Competition –
individuals attempting to utilize common
resources
Intraspecific competition - between
individuals of same population
Interspecific competition - between
different species
The Ecological Niche
• All of an organism’s adaptations, use of resources,
lifestyle, and habitat.
– Fundamental vs. Realized Niche
• Fundamental Niche - potential, idealized
ecological niche
• Realized Niche - actual, realized ecological
niche
– Limiting Factor
• Environmental resource that restricts an
organism’s niche because of limited availability.
The Ecological Niche
Example: Tale of Two Anoles
Green Anole Brown Anole
The Ecological Niche
Fundamental vs. Realized Niche
Fundamental
Niche of
Green Anole
Fundamental
Niche of
Brown Anole
Overl
ap
Brown anole out-competes
green anole, therefore . . .
COMPETITION
The Ecological Niche
Fundamental vs. Realized Niche
Realized
Niche of
Green Anole
Overl
ap Realized
Niche of
Brown Anole
The Ecological Niche
Limiting Resources
The Ecological Niche
Competitive Exclusion
no 2 species can occupy the same niche indefinitely.
one species is excluded from part of the niche
because of interspecific competition.
The Ecological Niche
Competitive Exclusion
The Ecological Niche
Competitive Exclusion
The Ecological Niche
Resource partitioning
coexisting species’ niches differ from each other in
more than one way.
Biological Communities
Succession:
Process of community development over time
Species in one phase of development are replaced by other species.
earlier species modify the environment
less competition for earlier species
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DisturbanceEvent that disrupts an ecosystem or community
• Natural disturbance
•tree falls, fires, hurricanes, tornadoes,
droughts, & floods
• Human–caused disturbance
•deforestation, erosion, overgrazing, plowing,
pollution, mining
• Disturbance can initiate primary and/or secondary
succession
Succession Two Types:
Primary succession
change in species composition in an environment that had not been established before.
no existing seed bank when development begins
pioneer community - initial community to develop
Secondary succession –
change in species composition after a disturbance destroys existing vegetation
Existing seed bank
Biological Communities
Primary succession –
Lichens
Mosses
Rocks
Biological Communities
Primary succession –
Rocks
Lichens
Mosses
Grasses
Shrubs
Biological Communities
Primary succession –
Rocks
Lichens
Mosses
Grasses
Shrubs
Trees
Biological Communities Secondary Succession
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Ecosystem Stability
Climax community – community that has reached a
“steady state”
Ecosystem stability – ecosystem that is resistant to
change.
Can an ecosystem have a climax community?
Increase biodiversity increase ecosystem stability