Fundamental Concepts in Behavioural Ecology

The relationship between behaviour, ecology, and evolution –Behaviour : The decisive processes by which individuals adjust their state and situation according to variation in their environment The value of a trait is determined by how it affects fitness relative to others in the population The scope of Behavioural Ecology

The hypothetico-deductive approach Competing hypotheses –Falsifiable Predictions of the hypothesis Tests of predictions –Situations in which the alternatives make different predictions –Falsification or corroboration

Evolutionary definitions Evolution: Change in gene frequencies over time –A population-level process Genotype: The allelic composition of an individual with respect to the locus(i) of interest Phenotype: The organism’s overall characteristics, or a subset of those characteristics Genome: All of the genetic information carried by an individual Environment: Everything external to the organism

A gene-centric view Genetic information is the target of selection –Organisms are vehicles for genes Genomes are mortal, genes are potentially immortal BUT, the fate of a given gene is affected by its degree of ‘cooperation’ with other genes

Analyzing selection 1.Compare traits with proxies of selection Relative reproduction Relative survival 2.Response to selection Change in allelic frequencies

What controls the phenotype? The “genetic” basis of fixed traits What does it mean that a trait is “genetically” or “environmentally” controlled? –DNA in a dish

Origin of phenotypic variance Thinking about variance V P = V G + V E + V G X E V G = V AG + V D + V I –V I = Epistatic effects –V D = Dominance interactions –V AG = additive genetic variance The only heritable kind

Heritability Heritability = h 2 = V AG / V P –The portion of the differences between individuals that is transmitted to descendants –A measure of a population’s ability to respond to selection –Measures resemblance among relatives vs. non-relatives

Measuring heritability I Artificial selection –Drawing time Strength of selection = S = P bar – X bar h 2 = R / S Estimates vary by generation Ritchie et al Anim. Behav. 52:603-

Measuring heritability II Parent-offspring regression –Compare traits between parents and offspring –Assign mates randomly –Slope of best fit line is observed heritability

Interpreting heritability Heritability estimates vary by population –Varying levels of V A Heritability estimates vary by environment –V E contributes to V P

Phenotypic plasticity Phenotypic plasticity is the capacity to produce different phenotypes according to variation in the environment –It can be adaptive or non-adaptive V E is a measure of expressed phenotypic plasticity Norms of reaction –Drawing time

Fitness When to measure? Genotypic fitness –Relative success of one allele (or a set of alleles) across two generations Individual fitness –Relative ability of a phenotype to produce mature descendants m/2007/12/richard-sandrak-aka-little- hercules.jpg

Evolution, selection, drift Selection pressure without evolution? –Evolution requires heritable variation Evolution without natural selection? –Mutation –Genetic drift Importance depends on pop size Does not produce adaptation –Random events

Adaptation Def 1: A trait that was fixed or stabilized by selection because of its effects on the inclusive fitness of its bearer in ancestral environments Def 2: The process by which a population evolves to be better suited to its environment

Adapting to the environment Four mechanisms –Darwinian mutation & selection –Phenotypic plasticity –Cultural adaptation –Niche construction

Inclusive fitness A simplified definition: –“The sum of the direct and indirect fitness effects of an individual's behaviors, where the direct fitness effect is the impact on the individual's fitness, and the indirect fitness effect is the impact on the fitness of its social partners, weighted by the degree of relatedness between the individual and its social partners.” (Ricklefs & Miller, 2001)

Recognizing genetic similarity The green beard Subtler indicators of genetic similarity –Kinship Kin selection: Natural selection for altruistic behavior directed toward kin

Hamilton’s rule An actor & a recipient Altruistic behavior will benefit the actor’s inclusive fitness when … br – c > 0 – b = benefit to recipient – c = cost to actor – r = relatedness of actor and recipient