Foods of Primary Consumers on Cold Desert Shrub-Steppe of Southcentral Idaho

Abstract

Trophic relationships of rabbits, black-tailed jack rabbits, pronghorn, sheep, and cattle were examined on the Idaho National Engineering Laboratory Site in southcentral Idaho. Grasses were the most important foods of lagomorphs and livestock. Pronghorn depended mostly on basin big sagebrush, common winterfat, and saltbushes. If jack rabbits increase in the future, severe competition for forage with livestock may result. Large portions of the shrub-steppe of Idaho are winter grazed by sheep (Ovis ah-es), cattle (Bos tuurus), and native wild herbivores. Unregulated grazing can lead to poor range condition, poor condition of wild herbivores, and poor livestock performance. Range managers must assess quantitatively the combined impacts of different herbivores on range resources before planning grazing operations. The Idaho National Engineering Laboratory (INEL) Site in southcentral Idaho is managed by the U.S. Department of Energy and the U.S. Bureau of Land Management lets grazing leases for about 60% of the area (Johnson 1978). Sheep and cattle use these areas and each grazes in common with wild herbivores but the domestic animals do not use the same areas. The most important wild herbivores on the site are pronghorn (Antelocapra americana) and rabbits (Sylvilagus spp). Blacktailed jack rabbit (Lepus calijornicus) populations may become periodically important. During the present study jack rabbit population densities were extremely low on the study area. The purpose of this paper is to report potential levels of diet competition between herbivores which use the INEL Site. Since the study area is typical of the shrub-steppe of southern Idaho, the results of this study have potential for guiding range management over wide areas of the northern Great Basin area.