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 Sparrow
Zonotrichia leucophrys
Breeding Territoriality:
Aggression, Mate Attraction,
Foraging, Care of Young
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Territoriality: How?
Spring: Increases in Day-length
Compared to Circadian Clock
Transmitted to Hypothalamus
“Right time”: Neuro-hormones Released,
Target Anterior Pituitary
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Territoriality: How?
Anterior Pituitary Releases Gonadotropins
into Bloodstream, Target Testis
Testis Releases Steroid Hormones
Secondary Sexual Characteristics,
Reproductive Behavior: Territoriality
Mechanisms: More Description than Prediction
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Territoriality: Why?
Adaptive Value vs Alternatives
Fitness: 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 Territoriality
Predict: 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 Behavior
Comparative Method
Cuvier: Anatomy, Paleontology
Newton Era
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Comparative Method
Comparative Anatomy for Phylogeny
Apply to Behavior: Phylogeny,
Later: Correlate Behavior with
Environment
Across Series Populations, Species, …
Does same environment produce same behavior?
Behavioral Convergence  Adaptation?
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Comparative Method
Correlations of Behavior & Environment
Suggest Hypotheses re Adaptation
Correlation Not Causality
Secondary 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 Drive
Natural Selection
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Natural Selection
Change in Gene Frequencies Due to
Variation in Lifetime Reproductive
Success Among Individual Phenotypes
Survival and Fecundity  Fitness
Inclusive Fitness
Different Genes  Different Phenotypes
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Natural Selection
Phenotypic Variance Within Population
Genetic Variation:
Contributes to Phenotypic Variance
Phenotypes Heritable
Different Phenotype: Different Fitness
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Levels of Selection
Gene
Individual: Natural Selection
Darwinian Fitness
Family: Kin Selection
Inclusive Fitness
Group, Deme, Species
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Selection and Adaptation
Natural Selection: Individual Fitness
Result: Population Adapts
Mean Fitness Increases
Fitness 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 Method
Functional Questions
Optimality Models to Predict Behavior:
Assume Optimizing Selection
Optimal, “best,” metaphor for adaptation
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Optimality Theory
Question In Behavioral Ecology
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

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 Set
List 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) Available
Physiological Requirement
Possible 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 Function
Maps Any Feasible Behavior onto
An Hypothesized “Currency of Fitness”
Hypothesis: Increase in Currency Will
Increase Survival, Reproduction
… Test Understanding
Deduce Prediction(s)
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Optimality Theory
Currency of Fitness
Rate of Energy Gain While Foraging
Probability of Starving
Offspring Produced/Year
Maximize Fitness Currency by
Optimizing Behavioral Strategy
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