Effects of migratory pattern on dynamics and persistence of patchy populations

We examine the effects of variation in migratory patterns on the dynamics of patchy populations. Many species are distributed across natural environments which are not continuous and are linked in complex ways.  Human land use activities further complicate these existing patterns. Freshwater organisms such as pond-breeding amphibians are striking examples of taxa with such spatially disjointed regional distributions, as are an ever-increasing number of marine and terrestrial species. We explore these issues in a matrix population model incorporating migration between patches of varying quality in a landscape with complex connectivity. Our model shows that population dynamics can be greatly affected by 1) interactions between variance in patch quality and asymmetries in access, 2) residence time in patches, and 3) temporal variation in patch quality and migratory survival rates. We examine these effects using a novel quantitative tool, fitness-density covariance, which quantifies the effects of variation in patch quality, movement patterns, and migratory survival rates on overall population growth. It is a powerful tool for the questions at hand because it clearly shows how and when local environments and abundance patterns interact to promote or diminish population growth and persistence. In many cases, average patch quality fails to predict the fate of a population, particularly when landscape connectivity biases dispersal towards or away from the best patches. The model also shows how elements of life history such as dispersal propensity can interact with changing landscape patterns to determine population persistence.  This is of particular relevance to vagile species in degraded habitats.