Comparative Nutritional Ecology of Montane Ungulates during Winter

Abstract

Comparisons of botanical and nutritional characteristics of winter diets of elk (Cervus elaphus nelsoni), mule deer (Odocoileus hemionus hemionus), and mountain sheep (Ovis canadensis canadensis) revealed sharp divergence in food niches. Deer diets contained the most browse and lignin, were intermediate in crude protein, and contained the least in vitro digestible dry matter (IVDDM). Mountain sheep diets were dominated by forbs and were consistently highest in protein and IVDDM. Cell solubles were higher and nonlignified cell wall lower in mule deer and mountain sheep diets compared with elk diets. Elk diets contained the most grass, were intermediate in IVDDM, and were lowest in crude protein. Protein and cell soluble content of diets were correlated with diet selectivity. These species ate less grass and more dicots when the crude protein and cell soluble content of grasses declined. Our findings are discussed in context of current theory on trophic ecology of wild ungulates. We propose that mule deer fit some aspects of this theory poorly and suggest that recent findings on their digestive physiology may explain this inconsistency. J. WILDL. MANAGE. 47(1):1-16 The process of diet selection is fundamental to understanding many aspects of ungulate ecology. An animal's body size and morphology limit the range of foods it can efficiently eat and assimilate (Hoffman 1973, Janis 1976, Kay et al. 1980). Food selection and assimilation ability are important determinants of the relative suitability of habitats for ungulates and are closely related to their social structures, patterns of dispersal, and tactics of predator avoidance (Bell 1970, Jarman 1974, Maddock 1979). Food choices affect community organization (Vesey-FitzGerald 1960, McNaughton 1978, Jarman and Sinclair 1979) and ecosystem function (Ellis et al. 1976; McNaughton 1976, 1979). Previous studies of trophic relations of wild ungulates have been largely observational, focusing on taxonomic and morphological differences in animal diets. Here we report experimental comparisons of nutritional attributes of winter diets of 3 montane ungulates: mule deer, elk, and mountain sheep. We test predictions of theory on physical, chemical, and botanical composition of ungulate diets relative to body size, social organization, digestive morphology, and changes in food