Genetic Structure of American Black Bears in the Desert Southwest of North America

Abstract American black bears (Ursus americanus) have recolonized parts of their former range in the Trans-Pecos region of western Texas after a \u3e40-year absence. Assessment of genetic variation, structuring, gene flow, and dispersal among bear populations along the borderlands of Mexico and Texas is important to gain a better understanding of recolonization by large carnivores. We evaluated aspects of genetic diversity and gene flow for 6 sampling areas of black bears in southwestern North America using genotypic data from 7 microsatellite loci. Our results indicated that genetic diversity generally was high in the metapopulation of black bears in northern Mexico and western Texas. The episodic gene flow occurring via desert corridors between populations in northern Mexico and those in western Texas has permitted the establishment of only moderate levels of genetic structuring. Bayesian clustering analyses and assignment testing depicted the presence of 3 subpopulations among our 6 sampling areas and attested to the generally panmictic nature of bear populations in the borderlands region. The potentially ephemeral nature of the small populations in western Texas and genotypic characteristics of bears recolonizing these habitats attest to the importance of linkages along this portion of the borderlands of the United States and Mexico to effectively conserve and manage the species in this part of its range

Movements and spaciotemporal variation in relation to food productivity and distribution, and population dynamics of the Mexican black bear in the Serranias del Burro, Coahuila, Mexico

Major subject: Wildlife Science.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/km² 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