Vertebrates

Vertebrates of alpine tundra are near the limits of their genetic tolerance, and thus the alpine provides a natural laboratory for the study of the ecology of these organisms in a climatically stressful environment. The alpine supports a greater species richness of vertebrate herbivores than does arctic tundra (Halfpenny and Southwick 1982). Hoffmann (1974) provided an extensive review of terrestrial vertebrates of arctic and alpine ecosystems, emphasizing circumpolar patterns. For a variety of reasons, however, vertebrates of alpine tundra are considerably less studied than are those of the Arctic, and much remains to be learned about the physiological and behavioral adaptations of vertebrates that allow this group to exist in this extreme and variable ecosystem. May (1980) offered some generalizations about the state of knowledge of alpine animals. Terrestrial systems are better known than aquatic systems; the magnitude of environmental variability is better known than its predictability and significance to populations of animals; life histories of animals are better known than their roles and functions; dynamics of single species are better known than interactions between and among species; habitat selection by animals is more often defined in terms of the perception of the investigator than in terms of the perception of the organism; the response of animals to patterns of vegetation is better known than the influence animals have in creating and maintaining those patterns; and densities of animals are better known than are patterns of dispersion and their causes. Those generalizations remain broadly accurate. The purpose of this chapter is to develop a perspective on the structure and function of the vertebrate fauna of alpine environments of the Southern Rocky Mountains, with an emphasis on the fauna found on Niwot Ridge. It considers the origin and ongoing development of the fauna and its biogeographic and ecological relationships. A pattern of distributions is described that is dynamic in space and time. A principal focus is the role of vertebrates to the structure and function of the tundra ecosystem, including both the biotic and physical impacts of vertebrate populations. Some attention is paid to vertebrate trophic guilds, but plant-animal interactions are detailed in this volume by Dearing (chapter 14).