Behavior: Levels of Explanation Recall N. Tinbergen Proximate: Mechanisms (How? Most Biology)...
Transcript of Behavior: Levels of Explanation Recall N. Tinbergen Proximate: Mechanisms (How? Most Biology)...
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Behavior: Levels of Explanation
Recall N. Tinbergen
Proximate: Mechanisms (How? Most Biology)
Ultimate: Adaptive Significance (Why?)
Example, Compare
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Male White-crowned Sparrow
Zonotrichia leucophrys
Breeding Territoriality
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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
Fitness: Survival & Reproduction
Defending Resources (Food, Nest Site)
By Excluding Conspecifics
Advances Reproductive Success
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Territoriality: Why?
Defended Resources on Territory
Attracts Mate, Food for Offspring
Single-Pair Territory Greater Reproductive Success
Than Alternatives
Assume Natural Selection & Adaptation
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Territoriality: Why?
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
Applied to Behavior: Initially for Phylogeny,
Later: Correlate Behavior with Environment
Across Series Populations, Species, …
Does same environment produce same behavior?
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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 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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Phenotypic Gambit
Constructing Model for Optimal Behavior
Incorporate Hypothesis:
Behavior and Fitness
Math: Deduce Prediction, Then Test
If we can predict, we understand.
Assigned: Review this lecture; Read next lecture.
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Introductory Topics
How do we invoke the concepts of Natural Selection to predict behavior?
What is “optimizing selection?” How do we apply the notion of optimizing selection in the “Phenotypic Gambit?”
How do we distinguish the comparative method from deductive modeling as ways to understand behavior?
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Phenotypic Gambit
Natural Selection Acts on Behavior – As with Anatomy & Physiology
“Phenotypic Gambit”~Ignore Details of Evolutionary Genetics~Ignore (Unnecessary) Details of Mechanisms~Optimization Model,
Predict Outcome of Selection
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Adaptation
Selection on Individuals Population Adapts
Fixed Environment Optimizing Selection:
~Mean Fitness Increases
~Fitness Variance Decreases
Phenotype “Optimized;” Optimization Models
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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 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