In nature, the populations of many, if not most, species are patchily distributed across the landscape, just as they are among islands in an archipelago (Chapter 22). Deer occur only where there are forest patches of suitable size, milkweeds occur only in open fields, and ducks need to be near water. Local populations are therefore usually separated from one another in space and are connected only occasionally by individuals that migrate between habitat patches. Moreover, some habitat areas that could, in principle, support populations of a given species are unoccupied. How does this kind of distribution influence the dynamics—