METAPOPULATION GENETICS AND THE EVOLUTION OF DISPERSAL

A Markovian extinction model that takes into account age structure of local populations allows consideration of the effects of demography an d successional dynamics on the evolution of migration. Analytical expr essions for the evolutionarily stable (ES) rates of dispersal are give n for cases in which newly recolonized sites attain carrying capacity within a single season. Using a low-fecundity numerical model, we find that an increase of the level of site saturation increases the disper sal rate. Ecological successions and unequal local extinction rates be tween newly colonized sites and established populations strongly affec t the ES dispersal rate. The frequency of genetic modifiers that enhan ce the rate of dispersal evolves negative correlations with deme age, with high-migration genotypes predominant among colonizers while progr essively declining in frequency as a deme ages. This suggests that bet ween-deme selection (colonization) favors migrants while within-deme s election favors low dispersers, which allows the coexistence of types with different dispersal rates. Because of the interaction between the two levels of selection, the relation between the ES dispersal rate a nd the deme maximal lifetime is nonmonotone. We suggest that life-hist ory traits other than dispersal might also experience antagonistic sel ective forces at the between- and within-deme levels.