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The Evolution-Ecology Connection

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Evolution: ‘unfolding’ – process by which species are altered

Species change over generations

New species appear

Species become extinct

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How are evolution and ecology related?

• Ecology involves understanding of relationships of organisms with each other and with their environment

• Evolution involves changes in species in response to interactions with each other and with their environment…

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Contributions to Modern Evolutionary Thought

“Malthusian catastrophe”

• Thomas Malthus – economist, social philosopher – populations of all organisms eventually out-grow available resources

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• Gregor Mendel (1822-1884): concepts and patterns of inheritance

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• Catastrophism- he Earth’s surface has been scarred by catastrophic natural disasters

• Charles Lyell: theory of uniformity – surface of earth has gradually changed, earth much older than previously recognized

"The Present is the Key to the Past"

Catastrophism Vs Uniformitarianism.

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Fig. 2.3Darwin’s Voyage

Charles Darwin: synthesis of theory of evolution based on natural selection

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Out of this study grew several related theories:

• one, evolution did occur; • two, evolutionary change was gradual, requiring

thousands to millions of years; • three, the primary mechanism for evolution was

a process called natural selection; and • four, the millions of species alive today arose

from a single original life form through a branching process called "speciation."

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Forces driving evolution:

over-reproduction

genetic variability

selective pressure

environment –(food, temperature, etc.)

disease

predators

survival and reproduction of organisms best suited to their environment

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• Read Scot Norris’ paper Evolution's "Driving Force" Shifts Based on Behavior, Study Says

http://news.nationalgeographic.com/news/2006/11/061116-lizard-evolution.html

• Read Jonathan Losos' paper "Adaptation and speciation in Greater Antillean anoles"

http://biosgi.wustl.edu/%7Elososlab/losos.2004.adaptivespeciationbook.pdf

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Genetics and Evolution• Trait: appearance/ability to carry out some

process Phenotype: appearance of an organism

due to a specific trait or combination of traits

• Gene: genetic information (region on a chromosome) which codes for a specific trait. Allele – variant form of a gene

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Natural selection can favor, disfavor, or conserve the genetic make-up of a population: Stabilizing Selection Directional Selection Disruptive Selection

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Stabilizing Selection- also known as ‘Purifying Selection’

• Stabilizing selection acts to impede changes in a population by acting against extreme phenotypes and favoring average phenotypes.- prevents divergence from form and function but genetic diversity decreases

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Directional Selection• Directional selection leads to changes in

phenotypes by favoring an extreme phenotype over other phenotypes in the population. Increase frequency independent of dominance

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Disruptive Selection- also called ‘Diversifying selection’

• Disruptive selection creates bimodal distributions by favoring two or more extreme phenotypes over the average phenotype in a population.- driving force of sympatric speciation- (Finch population Darwin)

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Fig. 2.18

‘Ecosystems’ ability to absorb shocks and disturbances

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• What is a species?‘A group of similar appearing organisms

which share the same gene pool’

• Species evolve to fill different niches• Example: Finch evolution in Galapagos

Islands• Result: Radial Evolution

– Single ancestral form– Many generations unique species for

different niches

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Fig. 2.10

Speciation of Finch on Galapagos Islands- C. Darwin

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How do new species arise?

1. Sympatric speciation

2. Allopatric speciation

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• occurs as a species fills different niches within the same habitat or geographic area– Spread of species into new areas– Founding population in isolated location– Geologic changes – gradual process

Sympatric speciation:

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• spatial isolation – occurs due to geographic isolation– Genetic changes (as ploidy levels in plants)– Disruptive selection: divergent genotypes

favored

Allopatric speciation:

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Geographic Variation Within Species

• Cline: measurable, gradual change in a trait over geographic region

• Ecotype: Population adapted to particular local environment

• Geographic isolate: reproductively isolated populations– subspecies

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Georgii Frantsevitch Gause • a theory which states that two species

competing for the same resources cannot stably coexist, if the ecological factors are constant. Either of the two competitors will always have an advantage over the other that leads to either the extinction of the inferior competitor or its evolutionary shift towards a different ecological niche.

Gause’s Law-

competative exclusive principle

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Geographic Isolation of Ensatina escholtzii populations in CA

• ‘ring species’ – geographically isolated populations surround uninhabitable area

• Adjacent populations can interbreed

• Reproductively incompatible at extremes (black)

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Local E.escholtzii

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Changes within a species are due to changes in its gene pool – causes:

• Selective pressures

• Genetic drift and bottleneck effects– Isolated populations– Effect greater in small populations

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Variation Within Populations• Variation in Plant Populations

Many plant species differ dramatically in form from one elevation to another.

Clausen et.al. found evidence of adaptation by ecotypes to local environmental conditions in Potentilla glandulosa.

Distinctive ecotypes- distinct entity of animal or plant or organism closely linked to its ecological surroundings

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Variation in Plant Populations

• Molecular and Morphological Information Hansen et. al. used randomly amplified

polymorphic DNA (RAPD) along with morphological data to support separation of three species of Potentilla.

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• Ecotypes – Potentilla glandulosa – sticky cinquefoil

• 3 ecotypes: Alpine Midelevation lowland

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• How genetically different are ecotypes?

• Work with Potentilla nivea (a species complex)

• Morphological (appearance) observations suggest three species

• Molecular analysis via RAPID study supports morphological species distinction

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Fig. 8.6

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Summary:• Organisms become ‘tailor made’ for

their role niche within an environment by processes of evolution

• New species arise from preexisting species

• New species arise as organisms become reproductively isolated

• Reproductive isolation may often result in genetically different populations

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Questions• How do we know that a species is a species if we

do not directly observe whether it can interbreed with other organisms? 

• If one population is the ancestor to another, how do we decide if they are more than one species? 

• Does extinction imply mistakes by an "intelligent designer"?

• How, in terms of Gause's law, does a catastrophic event influence subsequent evolutionary events.

• Which (and why) are more likely to become extinct, a highly specialized species extremely well adapted to a particular niche, or a less specialized generalist?