METAPOPULATION EXTINCTION AND GENETIC-VARIATION IN DISPERSAL-RELATED TRAITS

When the suitable habitat for a population is fragmented into relative ly isolated patches, an individual's probability of success in interpa tch migration may become low. If, in addition, the local demes inhabit ing the patches experience random extinctions, the persistence of the entire metapopulation can be threatened. A reduction in migration succ ess results in natural selection, and given genetic variation in dispe rsal-related traits, fragmentation may be followed by a change in disp ersal behaviour and capacity, which in turn can influence the persiste nce of the metapopulation. Using computer simulation, we investigate t he consequences of genetic variation in dispersal-related traits for t he probability of extinction following fragmentation. We find that wit hin-deme selection against dispersal can set off a critical phase, dur ing which the patch occupancy is low and the risk of extinction high. In this manner, genetic variation can pose a threat to persistence. Ho wever, if a metapopulation recovers from the critical phase, through r ecolonization of empty patches by efficient dispersers, the ensuing pe rsistence tends to be higher than would have been the case without gen etic variation. The severity of a critical phase depends on factors li ke the rapidity of the fragmentation process and the magnitude of the drop in survival.