| Black bear habitat use based on available digestible energy was investigated in the Serranias del Burro, Coahuila, Mexico, during 1998–2001. Reproduction, survival, and density of the bear population were also calculated during 1998–2001, and compared to results of a study conducted in the same area during 1991–1994. Production of key bear foods was estimated, and plotted based on a GIS vegetation map. Foods were also analyzed for digestible energy content, and then interpolated onto the GIS map using ArcMap and ERDAS, adjusting for percent canopy cover of species within different vegetation associations. Average digestible energy within female black bear home ranges were compared to digestible energy of seasonal locations for 1999 and 2000. Between 1991–1994 and 1998–2001, density appeared to increase (0.33 bears/km2 to 0.56 bears/km 2) using a modified Lincoln-Petersen estimator. Density was also estimated using a modified mark-resight technique during the 1998–2001 study, and was found to be 0.84 bears/km2, which is one of the highest published densities in North America. Cub survival decreased from 0.80 to 0.32 between the 2 studies, and it is suspected that mortality was due to intraspecific predation by adult males. Reproduction was similar between both studies until a mast failure in 2000–2001, which resulted in low reproduction. Adult females used areas that contained 27% more digestible energy than areas not used within their overall home ranges during fall 1999, and 20% more than areas not used during fall 2000. Patterns of food production across a landscape may influence effective density of bears within food patches, thus exposing adult females and cubs to high risk of mortality from other bears. Density dependence of bears may be directly affected by food availability through altered social dynamics, particularly in a desert environment where vegetation fluctuates with weather patterns. |
