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Note: The last part of chapter 1 (on clutch size) will be considered after discussion of chapter 2 in a topic “Life history trade-offs” Focal animal sample Time(min) 0:00 3:33 4:56 5:22 6:35 8:50 10:00 Behavior sit walk fight walk rest walk Scan sample Interval 0:00 0:30 1:00 etc... samples must be independent! Individual 1 2 3 4 5 walkwalk fight fight walk walkwalk walk walk ov walk rest feed walk feed 4 1 2 3 4 5 1 2 3 Focal behavior sampling Tally instances of aggressive acts over set time Why do animals play? Practice for learning adult skills Play stimulates pleasure centers Play is a side effect of high metabolism in endotherms Play enhances brain development Are hypotheses mutually exclusive? So…are these hypotheses mutually exclusive? You need to consider the approach of each hypothesis, including ultimate vs. proximate Why do animals play? Practice for learning adult skills Play stimulates pleasure centers Play side effect of high metabolism in endotherms Play enhances brain development List independent, dependent variables and how you investigate: Existing variation in pop’ns Experimentally produced variation Comparison of species When testing hypotheses Just because a hypothesized function appears to explain the behavior doesn’t mean that it is right. Always consider alternative hypotheses and of course you need to test hypotheses. Understand causal (proximate )vs. functional (ultimate) explanations Also – remember we are seeing currently the result of past selection. Consider the hyena pseudopenis…. Consider the hyena pseudopenis…. Why a pseudopenis? Dominant females have high T and are aggressive…they get the pp. from high T Pp serves to signal to females and reduces tensions among aggressive females during ‘greeting ceremony’ Sperm choice by females Moral: The function of a behavior/structure presently may not explain why it evolved in the past.. Over-adaptionism Consider the example of driving in US vs. Britain. drive on right drive on left Constraints on adaptation Animals are often limited in what can possibly evolve….another reason to avoid assuming adaptation Example: parental behavior in mammals vs. birds mammals nursing Bird eggs Comparative approach Social behavior in weaver birds Solitary, group territory, or colonial Comparative approach Crook (1964) Tried to find correlations between ecology and nesting behavior Aspects of diet Food distribution Predation pressure Habitat Weaver bird comparison Comparative approach Food type and predation pressure explained nesting behavior, mating system, sexual dimorphism Jarman (1974) similar approach with ungulates But there are issues with these early comparisons… Home range size and diet in primates Fruit/insectivores Leaf-eating Testis size vs. mating system 100 Multi-male 10 Testes weight Monogamous, or single male 1 1 10 100 Body weight Comparing multi-species Using a statistical approach w/quantifiable variables is more powerful and objective Confounding variables Continuous scale Independence of data points Pan t. Pan pan. 100 Gorilla 10 Pongo Testes weight Tamarins, marmosets 1 1 10 Body weight 100 Pan 100 Choosing genus instead of species level avoids statistical bias towards groups with many species Gorilla 10 Pongo Testes weight Saguinus Callitrix 1 1 10 100 Body weight Independence by using ‘contrasts’ Instead of using pure species data for analysis, use amount of difference (contrasts) between species.