A metapopulation is a set of geographically distinct local populations occupying discrete habitat patches. In some patches, the local population can become extinct—for example, if there are not enough reproductive females, or if there is a drought or other environmental hazard that depletes the resources used by the local population. Alternatively, individuals migrating from other patches can colonise an empty patch. Thus, the dynamics of a metapopulation depends on the relation between extinction and colonisation events.