The number and types of species found in a given place is determined by forces operating at two different spatial scales: species interactions such as competition and predation occur locally within a habitat, while dispersal among habitats operates at much larger scales. Dispersal is important for allowing species to coexist, even when competition or predation might otherwise lead to extinction. However, recent theory suggests that the importance of dispersal depends on the similarity of the habitats involved. If the habitats are very similar or too different, then dispersal is less effective in preventing extinction. The proposed work will provide one of the first tests of this body of theory on dispersal and diversity. The work takes advantage of a very convenient natural community that is found in the water-filled leaves of the purple pitcher plant. Each leaf contains a simple food web in which mosquito larvae feed on protozoa and rotifers, which in turn feed on bacteria. The bacteria feed on the dead insects, primarily ants, that fall into these leaves and drown. New leaves are rapidly colonized, suggesting that there is significant natural dispersal among leaves. Several migration experiments will be conducted to determine when and how migration affects species diversity in these communities and to test several general theories about how biodiversity is controlled. Ultimately, this work may be valuable for the design of nature reserves, as well as for developing management practices that affect migration such as roads and corridors.
