The effects of habitat fragmentation on persistence of source-sink metapopulations in systems with predators and prey or apparent competitors

We consider systems with one predator and one prey, or a common predator an d two prey species (apparent competitors) in source and sink habitats. In b oth models, the predator species is vulnerable to extinction, if productivi ty in the source is insufficient to rescue demographically deficient sink p opulations. Conversely, in the model with two prey species, if the source i s too rich, one of the prey species may be driven extinct by apparent compe tition, since the predator can maintain a large population because of the a lternative prey. Increasing the rate of predator movement from the source p opulation has opposite effects on prey and predator persistence. High emigr ation rate exposes the predator population to danger of extinction, reducin g the number of individuals that breed and produce offspring in the source habitat. This may promote coexistence of prey by relaxing predation pressur e and apparent competition between the two prey species. The number of sink s and spatial arrangement of patches, or connectivity between patches, also influence persistence of the species. More sinks favor the prey and fewer sinks are advantageous to the predator. A linear pattern with the source at one end is profitable for the predator, and a centrifugal pattern in which the source is surrounded by sinks is advantageous to the prey. When the di spersal rate is low, effects of the spatial structure may exceed those of t he number of sinks. In brief, productivity in patches and patterns of conne ctivity between patches differentially influence persistence of populations in different trophic levels. (C) 1999 Academic Press.