Genetic and phylogenetic consequences of island biogeography

Island biogeography theory predicts that the number of species on an island should increase with island size and decrease with island distance to the mainland. These predictions are generally well supported in comparative and experimental studies. These ecological, equilibrium predictions arise as a result of colonization and extinction processes. Because colonization and extinction are also important processes in evolution, we develop methods to test evolutionary predictions of island biogeography. We derive a populati on genetic model of island biogeography that incorporates island colonizati on, migration of individuals from the mainland, and extinction of island po pulations. The model provides a means of estimating the rates of migration and extinction from population genetic data. This model predicts that withi n an island population the distribution of genetic divergences with respect to the mainland source population should be bimodal, with much of the dive rgence dating to the colonization event. Across islands, this model predict s that populations on large islands should be on average more genetically d ivergent from mainland source populations than those on small islands. Like wise, populations on distant islands should be more divergent than those on close islands. Published observations of a larger proportion of endemic sp ecies on large and distant islands support these predictions.