A black bear metapopulation analysis for the Southern Appalachians

Black bears (Ursus americanus) once were found throughout the southern Appalachians, but because of overexploitation and habitat loss, their range was reduced by approximately two-thirds. Anthropogenic changes on the southern Appalachian landscape during the last 100 years have resulted in a patchy distribution of forest habitats and fragmented black bear populations. Consequently, bears in the southern Appalachians may exist as a metapopulation, i.e., localized populations that interact through periodic local extinctions and recolonizations. My objective was to determine whether classic metapopulation theory, with local extinction and recolonization rates being dependent on patch size and isolation, explains occupancy of black bear habitat patches in the southern Appalachians. I tested this hypothesis by using >10,000 black bear radiotelemetry locations from studies conducted in North Carolina, Tennessee, and Virginia to delineate habitat patches at various spatial scales and resolutions. These patch aggregates were generated by resampling the original habitat grid at increasingly coarser resolutions. Occupancy of each patch was determined based on recent black bear distribution data. Using a metapopulation developed by Hanski (1993) and nonlinear regression, I estimated 3 extinction and colonization parameters for each patch aggregate. The regression analyses produced significant models (P < 0.001, R² 0.691-0.896) for the 4 spatial scales that I examined. Consistent with metapopulation theory, as patch area increased and isolation decreased, the probability of occupancy increased. My results suggest that metapopulation theory is useful in explaining the spatial distribution of black bears in the southern Appalachians and that these models can be used to predict bear distribution based on future conditions. My results suggest that isolation, rather than patch area, is the major impediment to black bear range expansion. The utility of the model was demonstrated by the removal of several large patches. The probability of black bear occurrence decreased in many remaining patches. Also, I illustrated the effect of bear reintroductions as a conservation tool, by simulating colonization of several patches. Depending on which patches were targeted for reintroduction, probabilities of colonization in surrounding patches increased by as much as 56%. My study suggests that the degree of isolation may warrant more consideration when making regional management decisions. This may be particularly important for isolated bear populations where long-term population persistence may be dependent on immigration or for unoccupied patches with suitable habitat that are too isolated for natural recolonization.