Niche theory predicts that ecologically identical species cannot stably coexist in local communities. My aim was to investigate morphological diversity as a possible factor enabling the coexistence of a species-rich Microtus (Rodentia: Arvicolinae) fauna in a hotspot of North American mammalian diversity, the Greater Yellowstone Ecosystem (GYE). LOCATION: The Greater Yellowstone Ecosystem, North America. METHODS: Using in-hand morphological measurements of size and shape, I compared the morphologies of three North American vole species (Microtus spp.), in sympatry in the GYE and in allopatry across their ranges, in order to examine: (1) whether morphologies are fixed or plastic and (2) the degree of morphological character displacement or convergence in sympatric species. RESULTS: Support was found for plasticity of morphology for all three vole species: M. longicaudus, M. montanus and M. pennsylvanicus. However, Microtus individuals of all species from the GYE area of sympatry were more similar to each other than to allopatric individuals of the same species. MAIN CONCLUSIONS: Competition among these congeners is not manifested in morphological overdispersion. The response of these congeneric species to the same local ecological conditions is convergent. The relative strength of environmental conditions appears to be stronger than the strength of competitive interactions among the study species.

Specimen Records of all Animals used in the Morphometric AnalysesAppendix S2.JBiogeography_dryad_PAS.xls