Niche relationships within a guild of ungulate species in Yellowstone National Park, Wyoming, following release from artificial controls

Niche relationships and diet overlaps were compared among elk (Cervus elaphus), bison (Bison bison), bighorn sheep (Ovis canadensis), mule deer (Odocoileus hemionus), and pronghorn antelope (Antilocapra americana) between 1967–1970 and 1986–1988, a period when total ungulate numbers nearly tripled on Yellowstone's northern range. Ungulate species ratios on Yellowstone's northern winter range during the latter period were 100 elk : 10 mule deer : 3 bison : 2 pronghorns : 1 bighorns. Elk numbers were positively correlated to bison, mule deer, and pronghorn numbers (r2 = 0.76, 0.97, and 0.48, respectively, P < 0.01). Few other changes in habitat use or habitat overlap occurred, and diets for only 2 of the 10 species pairs, elk-bighorn (Spearman's rank order coefficient (RHO) = 0.55, P < 0.05) and mule deer – pronghorn (RHO = 0.64, P < 0.05), were significantly associated with each other. Bison consumed more grass and fewer sedges, mule deer more fringed sage (Artemisia frigida) and more rabbit-brush (Chrysot...