Tóm tắt
Two species of chipmunks, Eutamias dorsalis and E. umbrinus exclude each other from certain elevations on isolated mountain ranges in the central Great Basin. Competitive success is determined by habitat; dorsalis excludes umbrinus from the sparse pinon—juniper forests at lower elevations and umbrinus excludes dorsalis from the denser forests at higher altitudes. The two species occur together only in a very narrow strip of intermediate habitat. Observation of the behavior and interactions of the two species within this overlap zone resulted in the following explanation for the mutual exclusion. E. dorsalis, the more aggressive and more terrestrial species, chases umbrinus from those areas where the trees are so widely spaced that umbrinus must flee on the ground. The competitive advantage immediately shifts to the more social and arboreal umbrinus when the trees are sufficiently large and dense that their branches interlock. In these habitats umbrinus readily escapes dorsalis by fleeing through the trees over routes that the more aggressive species cannot follow. In such situations the aggressive nature of dorsalis actually becomes competitively disadvantageous because the more social umbrinus is so numerous that dorsalis wastes a great deal of time and energy on fruitless chases. The differences between the two species in aggressive behavior apparently represent adaptations to the density of cover and food resources in their habitats. The main mechanisms of the competitive interaction between these two chipmunks (interspecific aggression, the ability of the subordinate species to utilize some feature of the habitat to escape from the dominant species, and aggressive neglect on the part of the dominant species) may frequently be important in cases of competitive exclusion between highly mobile animals.
