RESEARCH ARTICLE Space Use Variation in Co-Occurring Sister Species: Response to Environmental Variation or Competition?

Coexistence often involves niche differentiation either as the result of environmental diver-gence, or in response to competition. Disentangling the causes of such divergence requires that environmental variation across space is taken into account, which is rarely done in empir-ical studies. We address the role of environmental variation versus competition in coexis-tence between two rodent species: Rhabdomys bechuanae (bechuanae) and Rhabdomys dilectus dilectus (dilectus) comparing their habitat preference and home range (HR) size in areas with similar climates, where their distributions abut (allopatry) or overlap (sympatry). Using Outlying Mean Index analyses, we test whether habitat characteristics of the species deviate significantly from a random sample of available habitats. In allopatry, results suggest habitat selection: dilectus preferring grasslands with little bare soil while bechuanae occurring in open shrublands. In sympatry, shrubland type habitats dominate and differences are less marked, yet dilectus selects habitats with more cover than bechuanae. Interestingly, bechua