Intra- and inter-specific dominance relationships among arctic and snowshoe hares

Abstract

The geographic ranges of arctic and snowshoe hares (Lepus arcticus and L. americanus) rarely overlap. In Newfoundland and elsewhere in North America, arctic hares occupy treeless barrens or tundra, whereas snowshoe hares inhabit forest. We explored the hypothesis that such allopatry reflects interference competition, an agonistic interaction in which snowshoe hares are behaviourally dominant. To assess both inter- and intra-specific dominance, we conducted a series of dyadic trials in outdoor pens and also observed interactions of free-ranging individuals. Five testable predictions were inferred, a priori, from competition theory and previous leporid studies: (i) heavier individuals are dominant, (ii) adults dominate juveniles, (iii) females dominate males when both are in breeding condition, (iv) males dominate females when neither are in breeding condition, and (v) adults in breeding condition dominate those that are not. With snowshoe hares, tests for predictions i and ii were inconclusive, and iii was probably verified (P = 0.03). With arctic hares, test results were inconclusive for i, verified for ii (P < 0.01), and rejected for iii and iv, dominance being unrelated to sex or breeding condition. Prediction v could not be tested intraspecifically, but arctic hares dominated snowshoe hares in 84 of 85 dyads, including those where snowshoes weighed more, or were in breeding condition and arctic hares were not. It is, therefore, highly unlikely that interference competition with snowshoe hares is responsible for the current restriction of arctic hares to barrens and tundra.