Distribution of mammals in the davis mountains, texas and surrounding areas
DeBaca, Robert S.
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This project focused on the dispersal and distribution patterns of mammals in or near the Davis Mountains, Texas. Data were obtained from existing museum and literature records and from extensive field sampling of the region, which resulted in the acquisition of more than 2,000 museum specimens and related data (Appendix A). The purpose of this research was to investigate regional and local patterns of mammalian biodiversity as these relate to dispersal and distribution in montane ecosystems at a regional scale in the Trans-Pecos and at a local scale in and near the Davis Mountains. In the first chapter, paleontological data suggested that now isolated mountain ranges in the Trans-Pecos were once connected in a north-south network. Research in that chapter examined modern patterns of biodiversity in the mountains that could have resulted from patterns inherited from Pleistocene distributions and dispersal routes of species in mixed-conifer forests or piñon-juniper-oak woodlands. Evidence presented in chapter one indicated that connectivity to source areas could have improved dispersal opportunities through highland corridors and montane areas. The second research chapter evaluated an observed pattern of greater species richness at a middle elevation study site in the Davis Mountains that was about 15 percent the size of a larger study site in the highlands of this mountain range. Rodents were the focus of research to find a partial explanation for this pattern, in which a dispersal filter may have allowed dispersal of some species but hindered others along an elevational gradient from lowlands to highlands. This pattern suggested a decrease in the body size of a lowland group of species along this gradient in response to a substrate that becomes more unavailable to larger burrowing rodents. That pattern was not statistically significant, but an alternative investigation showed that the smaller mid-elevation site likely had greater habitat variety in comparison to the high elevation one, which could have provided more microhabitats for more species to coexist at the smaller, more diverse site. In the final research chapter, biodiversity patterns were investigated for bats in relation to broad-scaled ecological patterns and site-specific resource partitioning that could account for the observed spatial and temporal distribution patterns. Along an elevational gradient, five species were specific to a smaller series of elevations and habitat types; whereas, twelve species were either too rare to analyze or were widespread throughout the sampled array of environmental conditions. Five species also showed elevational segregation by sex, with females occupying a lower range of elevations than males, which was a surrogate measure of warmer macrohabitat utilization by females. Lastly the most prolific sampling site, a semi-perennial pool, was analyzed for temporal differences in its use by month and by time of night. The results showed that vespertilionid bats dominated use of this resource during mid-summer and during the first two hours of the night and that molossid bats dominated its use after the first two hours and during the latter part of the summer. This partitioning could result from the thermoregulation constraints of the main vespertilionid species that concentrated activity early in the evening and during the warmer months of the sampling period. In response to vespertilionid use and to prevent collisions, the fast-flying, less maneuverable molossid bats may avoid the area until use by other bats dwindles both during the night and warmer months of the season.