Habitat structure and predators: choices and consequences for rodent habitat specialists and generalists

Both habitat structure and risk of predation are thought to influence rodent community composition in different habitats, but experiments on the degree to which these factors determine the use of habitat by rodents are lacking. I sought to discover (1) if cover density altered habitat choice and (2) if cover density affected the vulnerability to predators of two rodents, a habitat specialist and a habitat generalist. In laboratory experiments, the habitat specialist, the red-backed vole (Clethrionomys gapperi), preferred greater densities of both vertical (wall) and horizontal (ceiling) cover. The habitat generalist, the deer mouse (Peromyscus maniculatus), also preferred greater densities of vertical and horizontal cover, but its preferences were weaker and more inconsistent than those of C. gapperi In tests of vulnerability to domestic ferrets, C. gapperi were more vulnerable in arenas with less vertical cover, while P. maniculatus did not differ in vulnerability between the two vertical cover densities used. Vulnerability to predators in differing densities of horizontal cover was not tested because of the reduced differences in preference for this cover type between the rodent species. Risk of predation is one explanation for C. gapper's inherent preference for denser cover.