Natural Selection, Evolution, Natural Selection, Evolution, and Evolutionary Ecologyand Evolutionary Ecology

Dr. James Danoff-BurgDr. James Danoff-Burg

Columbia UniversityColumbia University

Levels of Ecological Levels of Ecological ExplanationExplanation

UltimateUltimate– Evolutionary influencesEvolutionary influences

ProximateProximate– Human influencesHuman influences– Abiotic changesAbiotic changes– Biotic interactionsBiotic interactions

Most ecologists explore the last three levelsMost ecologists explore the last three levels

Progress of Ecological Inquiry?Progress of Ecological Inquiry?

Explore plausible ultimate answersExplore plausible ultimate answers

If one is supported, stopIf one is supported, stop

If no ultimate answers are supported, If no ultimate answers are supported, explore proximate answersexplore proximate answers

RationaleRationale

Need to pitch the question at the right Need to pitch the question at the right levellevel

ExampleExample– Why are Penguins only in the Southern Why are Penguins only in the Southern

Hemisphere?Hemisphere?– ProximateProximate - insufficient food, too many - insufficient food, too many

predators, lack of shelter, etc.predators, lack of shelter, etc.– UltimateUltimate - historical and thus evolutionary - historical and thus evolutionary

distribution --> favored at presentdistribution --> favored at present

Two EvolEcol BranchesTwo EvolEcol Branches

IntraspecificIntraspecific– Relative selective value of different traitsRelative selective value of different traits– Origin of intraspecific diversityOrigin of intraspecific diversity

InterspecificInterspecific– Behavioral ecology (comparative studies)Behavioral ecology (comparative studies)– Systematics and phylogenySystematics and phylogeny

Common feature of all branches - Evolution!Common feature of all branches - Evolution!

EvolutionEvolution

Change through time within a lineageChange through time within a lineage Mechanisms / Producers of VariationMechanisms / Producers of Variation

– Genetic driftGenetic drift– Phenotypic plasticityPhenotypic plasticity– Natural SelectionNatural Selection

Natural Selection Natural Selection Evolution Evolution

Natural SelectionNatural Selection

Proposed by Darwin and WallaceProposed by Darwin and Wallace Evolutionary mechanismEvolutionary mechanism One way that variation exists and is One way that variation exists and is

maintained in a populationmaintained in a population Value is relative to local competitorsValue is relative to local competitors Only a negative actionOnly a negative action

– Only selection AGAINST a form of a traitOnly selection AGAINST a form of a trait– Never selection for a traitNever selection for a trait

Intraspecific VariationIntraspecific Variation

Possible sources:Possible sources:– Genetic driftGenetic drift– Phenotypic plasticityPhenotypic plasticity– Natural SelectionNatural Selection

How to differentiate between them?How to differentiate between them?– Genetic fixation / continuity through lineagesGenetic fixation / continuity through lineages– Use traits that do not change in response to Use traits that do not change in response to

changes in environmentchanges in environment

Today’s ActivityToday’s Activity

How do changes in a resource gradient affect How do changes in a resource gradient affect intraspecific diversity?intraspecific diversity?– Are these changes due to natural selection?Are these changes due to natural selection?

Choose an organism with the following Choose an organism with the following characteristics:characteristics:– Low vagilityLow vagility– Does not disperse aeriallyDoes not disperse aerially– Clearly marked adult stageClearly marked adult stage– Traits under study do not changeTraits under study do not change

Activity TasksActivity Tasks

Plan activityPlan activity Collect data and enter into eBiomeCollect data and enter into eBiome Analyze our dataAnalyze our data Wait for data from other sitesWait for data from other sites Jointly analyze all dataJointly analyze all data Make conclusions about relationshipMake conclusions about relationship Posit future studies to distinguish between Posit future studies to distinguish between

evolutionary mechanismsevolutionary mechanisms

Planning - To be Determined:Planning - To be Determined:

Environmental variableEnvironmental variable Experimental organismExperimental organism Organismal trait for studyOrganismal trait for study Statistical technique to use, justifyStatistical technique to use, justify