Great Basin Naturalist


Within the Craters of the Moon Lava Flow in southeastern Idaho are kipukas, islands of sagebrush habitat isolated by relatively barren lava. In 1979 I counted the number of species of plants, small mammals, and reptiles for a series of kipukas. The degree of isolation of a kipuka was not related to numbers of species found there; thus, these data do not support the equilibrium theory of island biogeography. For most of the study organisms lava is not a significant barrier to dispersal. Larger kipukas support larger numbers of species. For plants this relationship likely is a result of the increased topographic variety of larger kipukas, whereas for small mammal species minimum area requirements for maintaining populations are met only by larger kipukas. More distant kipukas showed increased density of small mammals possibly as a result of reduced predation. Patterns of distribution in this ecosystem are best explained, not by any all-inclusive community mechanism, but through the agglomerative contributions of a variety of population and community functions.