The Great Plains of the United States is an area of historically high ungulate species diversity. Large roaming herds of bison (Bison bison ) once coexisted with pronghorn (Antilocapra americana), elk (Cervus elaphus), mule deer (Odocoileus hemionus ), white-tailed deer (Odocoileus virginianus) and the now extinct Audubon bighorn sheep (Ovis canadensis auduboni) on the open range.
Custer State Park (CSP), South Dakota, manages the full suite of ungulates native to the Great Plains for wildlife viewing, hunting, and other purposes. Management is based on untested assumptions regarding forage production, and resource selection and overlap of the ungulate assemblage. Our goal was to gain empirical data on the spatial and temporal selection of resources by the ungulate assemblage in CSP. To achieve this goal, we developed a spatially-explicit model to predict forage production throughout the park, evaluated factors affecting bison and pronghorn spatial selection of resources, evaluated diet selection and overlap among the ungulate assemblage, and habitat overlap among the ungulate assemblage. We incorporated this information into a spatially-explicit linear optimization model which estimated optimal stocking densities for CSP.
We observed considerable individual heterogeneity in the mechanisms affecting bison and pronghorn resource selection. In general, we found that forage biomass was most important to bison and pronghorn resource selection in CSP, but only when placed in the context of unique seasonal stressors, such as water and human disturbance. These results indicate bison herds are likely to change foraging patterns in relation to unique seasonal stressors and changes in palatable forage availability. Limiting the amount of unpredictable disturbance, or allowing disturbance-free areas, during the calving season may be beneficial to female bison with young.
During most seasons, pronghorn selected areas of high forage biomass close to ponds and far from streams. Management and conservation of pronghorn populations should focus on forage production, but also consider human disturbance and the types of water sources that are available. Further, the amount of heterogeneity we found in both bison and pronghorn resource selection suggests analyses that pool locations across individuals will likely miss the full suite of factors affecting resource selection of ungulates, including gregarious species that form large groups.
We used microhistological techniques to estimate diet composition of each ungulate species, and calculated Schoener's index of dietary overlap, which ranges from 0 (complete separation) to 1 (complete overlap), between each species pair. Diet composition of each species followed a priori expectations based on the physiology and natural history of the species. Overall, annual dietary overlap was high between bison and elk (0.63), elk and white-tailed deer (0.60), pronghorn and mule deer (0.61), and white-tailed deer and mule deer (0.55). Annual overlap was lowest between bison and mule deer (0.08) and bison and pronghorn (0.16). In general, dietary overlap among ungulate species was greatest during the summer and lowest during the winter.
Habitat overlap among all species was highest during winter and lowest during the summer. Female bison and pronghorn, both sexes of bison and elk, and white-tailed deer and elk used habitat in a similar manner during most seasons. Our data are consistent with the hypothesis that coevolutionary divergence or competition has resulted in habitat partitioning among the ungulate assemblage, with overlap among ungulates occurring at high quality resources within these habitat patch edges.
We used spatially-explicit information of forage production, diet selection, space-use, and habitat overlap of an ungulate assemblage gained during our study to develop a model that used linear optimization to optimize stocking densities of bison, elk, pronghorn, mule deer, and white-tailed deer.Our results demonstrated the importance of incorporating diet overlap, habitat overlap, and resource selection in stocking density estimates, especially for large and diverse ungulate assemblages. The model we produced will be most useful to examine theoretical relationships related to stocking densities and forage production, and tradeoffs in optimizing ungulate population numbers, rather than a strictly applied estimate of ungulate carrying capacities. (Abstract shortened by UMI.)
|Advisor:||Millspaugh, Joshua J.|
|School:||University of Missouri - Columbia|
|School Location:||United States -- Missouri|
|Source:||DAI-B 73/11(E), Dissertation Abstracts International|
|Subjects:||Wildlife Conservation, Ecology, Natural Resource Management|
|Keywords:||Bison, Carrying capacity, Elk, Pronghorn, Resource selection, Ungulate assemblage|
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