behavior: levels of explanation
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Behavior: Levels of Explanation. Recall N. Tinbergen Proximate : Mechanisms (How ? Most Biology) Ultimate : Adaptive Significance (Why ?) Example, Compare . Male White-crowned Sparrow. Zonotrichia leucophrys. Breeding Territoriality. Territoriality: How ?. - PowerPoint PPT PresentationTRANSCRIPT
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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
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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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