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?

Spring: Increases in Day-length

Compared to Circadian Clock

Transmitted to Hypothalamus

“Right time”: Neuro-hormones Released,

Target Anterior Pituitary

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

Territoriality: Why?

Adaptive Value

Fitness: Survival & Reproduction

Defending Resources (Food, Nest Site)

By Excluding Conspecifics

Advances Reproductive Success

Territoriality: Why?

Defended Resources on Territory

Attracts Mate, Food for Offspring

Single-Pair Territory Greater Reproductive Success

Than Alternatives

Assume Natural Selection & Adaptation

Territoriality: Why?

Understand Significance of Individual Behavior and Mating Systems

Model Benefits & Costs of Territoriality

Predict: Why Individuals Territorial or Not

Understand Behavioral Diversity

Functional Significance of Behavior

Research Strategies

1. Comparative Method

2. Hypothetico-Deductive Method:

Predictive Modeling

Functional Significance of Behavior

Comparative Method

Cuvier: Anatomy, Paleontology

Newton Era

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?

Comparative Method

Correlations of Behavior & Environment

Suggest Hypotheses re Adaptation

Correlation Not Causality

Secondary to H-D method:

Phenotypic Gambit

Phenotypic Gambit

Selective Evolution Favors Certain Alleles

Commonly: Natural Selection on Individuals

Result: Populations Adapt to Environment

Evolutionary Genetics Optimization Model

Biological Evolution

Change in Gene Frequencies thru Time

What Drives Evolution?

Mutation Migration (Gene Flow)

Genetic Drift Meiotic Drive

Natural Selection

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

Natural Selection

Phenotypic Variance Within Population

Genetic Variation:

Contributes to Phenotypic Variance

Phenotypes Heritable

Different Phenotype: Different Fitness

Levels of Selection

Gene

Individual: Natural Selection

Darwinian Fitness

Family: Kin Selection

Inclusive Fitness

Group, Deme, Species

Selection and Adaptation

Natural Selection: Individual Fitness

Result: Population Adapts

Mean Fitness Increases

Fitness Variance Declines

Phenotype “Optimized”

Selection and Adaptation

Directional Selection (favor 1 extreme)

Destabilizing Selection (favor extremes)

Optimizing (Stabilizing) Selection

Optimizing Selection

Optimality Theory

Hypothetico-Deductive Method

Functional Questions

Optimality Models to Predict Behavior:

Assume Optimizing Selection

Optimal, “best,” metaphor for adaptation

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.

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?

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

Adaptation

Selection on Individuals Population Adapts

Fixed Environment Optimizing Selection:

~Mean Fitness Increases

~Fitness Variance Decreases

Phenotype “Optimized;” Optimization Models

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

Optimality Theory

Identify Strategy Set

List Possible Behaviors

Discrete (Eat some prey, reject others)

Continuous (Time in food patch)

Optimality Theory

Identify Applicable Constraints

Total Time (or Energy) Available

Physiological Requirement

Possible vs Impossible

(Cannot Search for Food &

Handle Food Simultaneously)

Optimality Theory

Listing Constraints: “Phenotypic Gambit”

Ignore Genetic Constraints,

Usually Don’t Know What They Are

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)

Optimality Theory

Currency of Fitness

Rate of Energy Gain While Foraging

Probability of Starving

Offspring Produced/Year

Maximize Fitness Currency by

Optimizing Behavioral Strategy