Chapter 5: Evolution, Biodiversity
& Population Ecology www.aw-bc.com/Withgott

Evolution
 genetic change in populations of organisms across generations.
 modifications
– appearance: www.aw-bc.com/Withgott

Evolution
– functioning: beaks in honeycreepers www.aw-bc.com/Withgott

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
 Adaptation : trait that promotes success of a species

Effects of Natural Selection on Genetic
Variation
 Mutations : 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 selection
 selection that drives a feature in one direction www.aw-bc.com/Withgott

Stabilizing selection
 preserves status quo, no changes www.aw-bc.com/Withgott

Disruptive Selection
 traits diverge into two or more directions www.aw-bc.com/Withgott

Evidence of Natural Selection
 Selective breeding
 breeding of domesticated animals and plants
– dog and cat breeds
– variations of Brassica oleracea
– artificial selection

Biodiversity
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Total of all organisms in the area
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– 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
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 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 www.aw-bc.com/Withgott

Species Vulnerable to Extinction
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 some species may be more vulnerable than others due to change in environmental conditions
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– climate change rise and fall of sea level arrival of harmful species extreme weather events (drought, flood, etc.)
Endemic : single small population present only in a particular type of environment: Attwater chicken

Attwater Chicken
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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

www.aw-bc.com/Withgott
 Ecological Organization

Habitat, Niche and Specialization
 Habitat: living and non-living elements around a species
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– thriving of a species depends on patterns of habitat use each species' habitat is scale dependent
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– habitat selection is possible if the species is mobile the survival of the species depends if the habitat is suitable or not

Niche
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 a species' niche reflects its use of resources and functional role in the ecosystem
"job" specialists and generalists
– Prairie dog
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 eats grasses and keeps grass low for predator control more grass grown around burrow because
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– airiates soil by digging soil becomes richer near burrows because of dung burrow houses other animals when empty (snakes, rabbits, owls)

Population Ecology
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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 www.aw-bc.com/Withgott

Uniform www.aw-bc.com/Withgott

Clumped www.aw-bc.com/Withgott

Population Ecology
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 sex ratio : depends on the behavior (monogamous or polygamous) of the species, type of reproduction
(autofecundates or different sexes) age structure : age structure diagrams www.aw-bc.com/Withgott

Population Ecology
 birth and death rates : survivorship curves
– type I: higher mortality at older age
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– type II: equal rate of death at any age type III: higher rate of death at younger age www.aw-bc.com/Withgott k-selected r-selected

Population Ecology
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Immigration emigration growth rate
Unregulated population increase : shows exponential growth= J curve
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– 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
THE END