An experimental test of the causes of small‐scale phenotypic differentiation in a population of great tits

Phenotypic differentiation between populations is thought to occur mainly at spatial scales where gene‐flow is restricted and selection regimes differ. However, if gene flow is nonrandom, dispersal may reinforce, rather than counteract, evolutionary differentiation, meaning that differences occurring over small scales might have a genetic basis. The purpose of this study was to determine the cause of differences in mean phenotype between two parts of a population of great tits Parus major, separated by