Behavior: Levels of Explanation

Recall N. Tinbergen

Proximate: Mechanisms (How? Most Biology)

Ultimate: Adaptive Significance (Why?)

Example: Compare Levels

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Male White-crowned SparrowZonotrichia leucophrys

Breeding Territoriality:Aggression, Mate Attraction,Foraging, Care of Young

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Territoriality: How?

Spring: Increases in Day-lengthCompared to Circadian ClockTransmitted to Hypothalamus

“Right time”: Neuro-hormones Released,Target Anterior Pituitary

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Territoriality: How?

Anterior Pituitary Releases Gonadotropinsinto Bloodstream, Target Testis

Testis Releases Steroid HormonesSecondary Sexual Characteristics,Reproductive Behavior: Territoriality

Mechanisms: More Description than Prediction

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Territoriality: Why?

Adaptive Value vs AlternativesFitness: Survival & Reproduction

Defending Resources - Food, Mate, Nest Site -By Excluding Conspecifics

Advances Reproductive Success

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Territoriality: Why?

Single-Pair Territory Greater Reproductive Success

Than Alternatives

Fitness Value, Functional Significance

Assume Natural Selection & Adaptation

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Why Questions

Understand Significance of Individual Behavior and Mating Systems

Model Benefits & Costs of TerritorialityPredict: Why Individuals Territorial or Not

Understand Behavioral Diversity

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Functional Significance of Behavior

Research Strategies

1. Comparative Method

2. Hypothetico-Deductive Method:Predictive Modeling

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Functional Significance of BehaviorComparative Method

Cuvier: Anatomy, Paleontology

Newton Era

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Comparative Method

Comparative Anatomy for Phylogeny

Apply to Behavior: Phylogeny,

Later: Correlate Behavior with EnvironmentAcross Series Populations, Species, …

Does same environment produce same behavior?

Behavioral Convergence Adaptation?

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Comparative Method

Correlations of Behavior & EnvironmentSuggest Hypotheses re Adaptation

Correlation Not CausalitySecondary to H-D method:

Phenotypic Gambit

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Phenotypic Gambit

Selective Evolution Favors Certain Phenotypes; Presumably Alleles

Commonly: Natural Selection on Individuals

Result: Populations Adapt to Environment

Evolutionary Genetics Optimization Model

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Biological Evolution

Change in Gene Frequencies thru Time

What Drives Evolution?

Mutation Migration (Gene Flow)

Genetic Drift Meiotic DriveNatural Selection

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Natural Selection

Change in Gene Frequencies Due to Variation in Lifetime Reproductive Success Among Individual Phenotypes

Survival and Fecundity FitnessInclusive Fitness

Different Genes Different Phenotypes

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Natural Selection

Phenotypic Variance Within Population

Genetic Variation:Contributes to Phenotypic VariancePhenotypes Heritable

Different Phenotype: Different Fitness

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Levels of SelectionGene

Individual: Natural SelectionDarwinian Fitness

Family: Kin SelectionInclusive Fitness

Group, Deme, Species

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Selection and Adaptation

Natural Selection: Individual Fitness

Result: Population AdaptsMean Fitness IncreasesFitness Variance Declines

Phenotype “Optimized”

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Selection and Adaptation

Directional Selection (favor 1 extreme)

Destabilizing Selection (favor extremes)

Optimizing (Stabilizing) Selection

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Optimizing Selection

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Optimality Theory

Hypothetico-Deductive MethodFunctional Questions

Optimality Models to Predict Behavior:Assume Optimizing Selection

Optimal, “best,” metaphor for adaptation

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Optimality Theory

Question In Behavioral Ecology

Strategy Set (behavior, animal can do) Constraints (environment, animal can’t do) Objective Function

Hypothesize Currency of Fitness

Deduce Optimal Solution, Prediction

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Optimality Theory

Identify Strategy SetList Possible Behaviors

Discrete (Eat some prey, reject others)

Continuous (Time in food patch)

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Optimality Theory

Identify Applicable Constraints

Total Time (or Energy) AvailablePhysiological RequirementPossible vs Impossible

(Cannot Search for Food &Handle Food Simultaneously)

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Optimality Theory

Listing Constraints: “Phenotypic Gambit”

Ignore Genetic Constraints,Usually Don’t Know What They

Are

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Optimality Theory

Construct Objective FunctionMaps Any Feasible Behavior ontoAn Hypothesized “Currency of Fitness”

Hypothesis: Increase in Currency WillIncrease Survival, Reproduction

… Test Understanding

Deduce Prediction(s)25

Optimality Theory

Currency of FitnessRate of Energy Gain While

ForagingProbability of StarvingOffspring Produced/Year

Maximize Fitness Currency by Optimizing Behavioral Strategy

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