EVOLUTION OF DISPERSAL RATES IN METAPOPULATION MODELS - BRANCHING ANDCYCLIC DYNAMICS IN PHENOTYPE SPACE

We study the evolution of dispersal rates In a two parch metapopulatio n model. The local dynamics in each patch are given by difference equa tions, which, together with the rate of dispersal between the patches, determine the ecological dynamics of the metapopulation. We assume th at phenotypes are given by their dispersal rate. The evolutionary dyna mics in phenotype space are determined by invasion exponents, which de scribe whether a mutant can invade a given resident population. If the resident metapopulation is at a stable equilibrium, then selection on dispersal rates is neutral if the population sizes in the two patches are the same, while selection drives dispersal rates to zero if the l ocal abundances are different. With non-equilibrium metapopulation dyn amics, non-zero dispersal rates can be maintained by selection. In thi s case, and if the patches are: ecologically identical, dispersal rate s always evolve to values which induce synchronized metapopulation dyn amics. If the patches are ecologically different, evolutionary branchi ng into two coexisting dispersal phenotypes can be observed. Such bran ching can happen repeatedly, leading to polymorphisms with more than t wo phenotypes. If there is a cost to dispersal, evolutionary cycling i n phenotype space can occur due to the dependence of selection pressur es on the ecological attractor of the resident population, or because phenotypic branching alternates with the extinction of one of the bran ches. Our results extend those of Holt and McPeek (1996), and suggest that phenotypic branching is an important evolutionary process. This p rocess may be relevant for sympatric speciation.