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 selection1. 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

http://discovermagazine.com/2007/mar/eye-color-explained/eyes-400.jpg

Origin of phenotypic variance

• Thinking about variance

• VP = VG + VE + VG X E

• VG = VAG + VD + VI

–VI = Epistatic effects

–VD = Dominance interactions

–VAG = additive genetic variance• The only heritable kind

Heritability• Heritability = h2 = VAG / VP

– 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 = Pbar – Xbar

• h2 = R / S

• Estimates vary by generation

Ritchie et al. 1996 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 VA

• Heritability estimates vary by environment–VE contributes to VP

Phenotypic plasticity• Phenotypic plasticity

is the capacity to produce different phenotypes according to variation in the environment– It can be adaptive or

non-adaptive

• VE is a measure of expressed phenotypic plasticity

• Norms of reaction– Drawing time

http://weblog.ceicher.com/archives/tanlines.jpg

http://wfsc.tamu.edu/faculty/tdewitt/webpage.htm

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 http://

reneeashleybaker.files.wordpress.com/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

http://biologybk.st-and.ac.uk/cultures3/pix/deWfig1.jpg

http://home.earthlink.net/~gastropod/bvrdm.JPG

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