Persistence of Dispersal-limited Species in Structured Dynamic Landscapes

Dynamic landscape models have generally assumed random distributions of habitat although real landscapes show spatial organization at many scales. To explore the role of spatial structure in determining the frequency of dispersal-limited forest species, we used a cellular landscape model divided into two zones. Zones were distributed in a random, clustered, or regular spatial pattern. Within each zone habitat cells were randomly destroyed and regenerated, and habitat density and turnover rate were systematically varied. A hypothetical habitat-limited species dispersed between adjacent habitat cells. All trials showed a reduced species frequency relative to a static landscape. Reduction was greater at low habitat density (P = 0.30) than at high density (0.90) suggesting the importance of habitat connectivity in controlling species frequency. The greatest reduction occurred when habitat was concentrated in a small, regularly distributed zone at low habitat density reflecting the enforced isolation of individual habitat cells. Very little reduction was observed when habitat cells were packed into a small clustered zone, a situation promoting connectivity between cells. Moderate–severe frequency reduction occurred when habitat turnover was concentrated in a clustered zone at high habitat density, but little was observed when turnover was widely distributed in a regular or random pattern. These results can be interpreted in terms of a source-sink function in which spatial pattern controlled the degree of contact between landscape zones and determined opportunities for dispersal between habitat cells. We conclude that clustering of forest habitat has the potential to maintain herb species frequency in sparsely forested landscapes. Conversely, clustering of forest disturbance in heavily forested regions, or regular distribution of forest stands (as often occurs in agricultural regions) creates areas which are difficult to colonize, and should be avoided.