Resource partitioning by mammalian herbivores in the high Arctic.

Willow (Salix arctica) and sedges (Carex stans and Eriophorum triste) were the dominant plants available as forage for herbivores in the high Arctic of Greenland. Willow leaves were of high quality as forage in early stages, of phenology, but crude protein and digestibility declined markedly by late stages whereas sedges, remained high in forage quality throughout the growing season. Densities of fecal pellets indicated that muskoxen (Ovibos moschatus) made heaviest use of sedge-dominated vegetation types in both winter and summer, although increased use of willow communities was observed in early summer. Hares (Lepus arcticus) favored willow-dominated communities in both winter and summer. Evidence of collared lemming (Dicrostonyx groenlandicus) winter use was mainly in willow-dominated communities where snow had accumulated, whereas in summer they were present in drier habitas dominated by willows, but with greater plant diversity. Analyses of plant tissues in feces indicated that graminoids composed over 60% of the diet of muskoxen in winter and over 40% in summer. Willows were of nearly equal importance in the muskox diet in summer, and forbs, Dryas integrifolia, and moss collectively composed over 20% of the diet in both summer and winter. Grass accounted for nearly 50% of the diet of hares in both summer and winter, with willows, forbs, and moss accounting for most of the remainder. Willows and graminoids dominated the diet of lemmings, with willows being somewhat more important in summer and graminoids in winter. Moss was a noteworthy dietary component of lemmings. Differences in body and digestive-tract morphology among the three mammalian herbivores account for differences in locomotive efficiency, predator avoidance, and foraging efficiency which interact with vegetation quality, density, and patchiness. The resulting patterns of use of the landscape result in minimal overlap in use of forage resources and help to explain the distribution and co-existence of high Arctic herbivores.