Metapopulation Extinction and Genetic Variation in Dispersal-Related Traits

When the suitable habitat for a population is fragmented into relatively isolated patches, an individual's probability of success in interpatch migration may become low. If, in addition, the local demes inhabiting the patches experience random extinctions, the persistence of the entire metapopulation can be threatened. A reduction in migration success results in natural selection, and given genetic variation in dispersal-related traits, fragmentation may be followed by a change in dispersal behaviour and capacity, which in turn can influence the persistence of the metapopulation. Using computer simulation, we investigate the consequences of genetic variation in dispersal-related traits for the probability of extinction following fragmentation. We find that within-deme selection against dispersal can set off a critical phase, during which the patch occupancy is low and the risk of extinction high. In this manner, genetic variation can pose a threat to persistence. However, if a metapopulation recovers from the critical phase, through recolonization of empty patches by efficient dispersers, the ensuing persistence tends to be higher than would have been the case without genetic variation. The severity of a critical phase depends on factors like the rapidity of the fragmentation process and the magnitude of the drop in survival.