Habitat partitioning among co-occurring, ecologically similar species is widespread in nature and thought to be an important mechanism for coexistence. The factors that cause habitat partitioning, however, are unknown for most species. We experimentally tested three alternative hypotheses to explain habitat partitioning among two species of co-occurring burying beetle (Nicrophorus) that occupy forest (N. orbicollis) and wetland (N. hebes) habitats. Captive experiments revealed that the larger N. orbicollis (forest) was consistently dominant to N. hebes (wetland) in competitive interactions for carcasses that they require for reproduction. Transplant enclosure experiments in nature revealed that N. hebes had poor reproductive success whenever the dominant N. orbicollis was present. In the absence of N. orbicollis, N. hebes performed as well, or better, in forest versus its native wetland habitat. In contrast, N. orbicollis performed poorly in wetlands regardless of N. hebes' presence. When in the presence of N. hebes, N. orbicollis buried carcasses deeper which may provide a competitive advantage in forests, but further compromise their reproductive success in wetlands. Overall, our results support the recently described Competitive exclusion–tolerance rule, where the competitively dominant N. orbicollis excludes the subordinate N. hebes from otherwise suitable forest habitat, while the subordinate N. hebes is uniquely able to tolerate the challenges of breeding in wetlands.

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