Chapter 5: Evolution, Biodiversity & Population Ecology

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Evolution

genetic change in populations of organisms across generations.

modifications – appearanceappearance:

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Evolution

– functioningfunctioning: beaks in honeycreepers

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Natural Selection

explains the great variety of living organisms. derives from several premises noticed in

nature

Natural Selection Premises

constant struggle of organisms to survive and mate

organisms tend to produce more offspring that can survive.

individuals of the same species are not identical– variation

Variation

genetical differences environment within which genes are

expressed interaction between genes and environment AdaptationAdaptation:: trait that promotes success of a

species

Effects of Natural Selection on Genetic Variation

MutationsMutations: : accidental changes in the nucleotide sequence of the DNA

addition deletion substitution

Sexual Reproduction also Generates Variation

recombination of genes produces a novel combination generating variation– directional selection– stabilizing selection– disruptive selection

Directional selectionDirectional selection

selection that drives a feature in one direction

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Stabilizing selectionStabilizing selection

preserves status quo, no changes

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Disruptive Selection

traits diverge into two or more directions

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Evidence of Natural Selection

Selective breedingSelective breeding breeding of domesticated animals and plants

– dog and cat breeds– variations of Brassica oleracea– artificial selection

Biodiversity

Total of all organisms in the area– diversity of species– gene pool– populations– communities

Evolution generates biological diversity– as of 2008 1:3 amphibians, 1:7 birds and 1:5 mammals is

considered endangered or threaten (National Geographic) Species: organism that is able to reproduce and

have viable offspring

Speciation: Allopatric & Sympatric

Allopatric: species form due to physical separation

mutations can occur independently members of different populations don't mate populations continue diverging through time single species can generate multiple species

through time

Separation of Populations

glacial ice sheets during ice ages change of course of major rivers rise of mountain ranges evaporation of major lakes into smaller bodies of water temperature variation causing migration of plant populations

creating new patterns of animal/plant distribution isolation must remain for thousands of generations reunion of populations may occur, but if they are not able to

interbreed, two or more new species have emerged.

Sympatric

reproductively isolated due to behavioral causes

feeding at different times of the day feed at different sites mating on different times of the year hybridization in some plants mutations causing change in number of

chromosomes

Diversification

as a result of numerous speciation events phylogenetic trees explain differences and

similarities between species Speciation and extinction natural process that takes 1-10 million years

Diversification

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Species Vulnerable to Extinction

some species may be more vulnerable than others due to change in environmental conditions

– climate change– rise and fall of sea level– arrival of harmful species– extreme weather events (drought, flood, etc.)

EndemicEndemic: single small population present only in a particular type of environment: Attwater chicken

Attwater Chicken

1 million individuals in 1900 50 or so individuals today habitat disruption

– oil industry, housing, cattle, rice fields

predators (snake, rat, skunk) diseases weather collision (fence, cars) fire ants (kill chicks)

Levels of Ecological Organization

Species Population Communities Ecosystems Biosphere

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Habitat, Niche and Specialization

HabitatHabitat: living and non-living elements around a species– thriving of a species depends on patterns of

habitat use– each species' habitat is scale dependent– habitat selection is possible if the species is

mobile– the survival of the species depends if the habitat

is suitable or not

Niche

a species' niche reflects its use of resources and functional role in the ecosystem

"job" specialists and generalists

– Prairie dog eats grasses and keeps grass low for predator control more grass grown around burrow because

– airiates soil by digging– soil becomes richer near burrows because of dung

burrow houses other animals when empty (snakes, rabbits, owls)

Population Ecology

Population size: number of individuals present at a given time

– Attwater chicken- 1 million to 50 individuals

Population density: number of individuals per population per unit area

– golden toad- large population in a small area

Population distribution: spatial arrangement of organisms within an area. There are 3 types.

Population Distribution: Random

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Uniform

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Clumped

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Population Ecology

sex ratio: depends on the behavior (monogamous or polygamous) of the species, type of reproduction (autofecundates or different sexes)

age structure: age structure diagrams

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Population Ecology

birth and death rates: survivorship curves– type I: higher mortality at older age– type II: equal rate of death at any age– type III: higher rate of death at younger age

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k-selected

r-selected

Population Ecology

Immigration emigration growth rate Unregulated population increaseUnregulated population increase: : shows exponential

growth= J curve– carrying capacity causes logistic growth curve (S curve) to

show– caused by an environmental resistance (water, food,

shelter, predators, disease)

Density-dependent factors

its influence is affected by the population density– competition

food shelter mate water s-shaped curve

Density-independent factors

influence is not affected by population density; can eliminate large numbers of individuals without regard to its density

extreme temperatures catastrophic climate events fires volcano eruptions

Biotic Potential vs Reproductive Strategy

k-selected (k stands for Carrying capacity) low biotic potential long gestation period protects offspring as an investment for

species survivor relative few offspring during lifetime type 1 curve

– eg: humans, whale, rhino, elephant

r-selected (r stands for rate) focus on quantity not quality

– high biotic potential– large number of offspring– survivor of offspring depends on chance– type 3 curve– eg. fish, frogs, snails

Conservation of Biodiversity

social and economic factors– human behavior towards environment– economy vs environmental protection

protection of environment– began without much government support– even today governments may not have the funds– ecotourism is the key

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