Niche Separation Of Seven North American Ungulates On The National Bison Range, Montana.
Mccullough, Yvette Blazzard
1980
Abstract
Niche relationships of seven North American ungulates were studied on the National Bison Range, Montana. The species studied were bison (Bison bison), pronghorn (Antilocapra americana), elk (Cervus canadensis canadensis), bighorn sheep (Ovis canadensis canadensis), white-tailed deer (Odocoileus virginianus ochrourus), mule deer (O. hemionus hemionus), and the mountain goat (Oreamnos americanus). Spatial distribution, food habits, behavioral interactions, and characteristics of the habitat were evaluated. Habitat variables consisted of slope, aspect, elevation, range condition, broad vegetation types, vegetation types based on dominant plant species, edge effect, major and minor topographic features, use of exposed bedrock, distance from rocks, roads, and types of water. The relationship of each ungulate species to each variable was determined. Niche breadth and overlap were quantified for each variable. Interspecific relationships were illustrated by cluster patterns. Finally, niche overlap and cluster patterns for all variables were shown for all seven ungulate species. The total overlap is not necessarily the best representation of the dynamic relationships between the species. The variables were not independent, so the overlap was calculated as an arithmetic mean of the values for each variable. In addition, all variables were weighted equally in the analysis; however, one variable may have a very large influence on the interspecific relationships. The use of resources by white-tailed deer and pronghorn, for example, had an overlap in the same range as the overlap between elk, bighorn sheep and mule deer. The use of different vegetation types by white-tailed deer and pronghorn reduces the actual overlap. This impact is not reflected in the overlap value because other variables outweigh it. This study emphasizes the need for evaluation of each resource in an overall synthesis, rather than just a mathematical result, for explaining patterns of ungulate association. Niche overlap was found to be low on at least one axis of the niche hypervolume. High overlap on one or several resources was balanced by low overlap on another resource. Low overlap occurred for different variables for each pair of ungulates. Interspecific relationships shifted seasonally. The least overlap of all variables was in spatial distribution. Differences in food habits were important for some species pairs. A reevalution of the stress on management for good and excellent classes of range condition on the Refuge was recommended. Bighorn sheep, elk and mule deer had the highest overlap with each other in use of all 14 variables combined. This indicates that these three species are the most liable to compete with each other when resources are limited. White-tailed deer and mountain goats were the least similar in use of all resources.Subjects
American Bison Montana National Niche North Range Separation Seven Ungulates
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