Conclusion
Functional explanations for herbivore coexistence rely largely on our knowledge of differences in species’ resource niches (Prins & Olff 1998; Arsenault & Owen-Smith 2011; Kartzinel et al. 2015), whereas population dynamics and diversity are normally linked with demography and reproductive rates (Sinclair 2003; Owen-Smith 2006). Our results suggest that these explanations might be mismatched. Instead, it seems that species’ fitness is sufficiently similar to enable coexistence over a wide range of niche overlaps, which implies that fitness equivalence is a more important condition for species’ coexistence than niche partitioning. By contrast, niche partitioning is closely related to species’ invasion growth rates and, therefore, to their population dynamics. Thus, MCT provides valuable new insights into understanding herbivore communities. In particular, MCT demonstrates that concepts linking herbivore functional traits with fitness, which traditionally emphasize putative differences among species, should expand their focus to include more detailed evaluation of processes that ensure similarities in species’ abilities to convert poor quality resources (plants) into offspring.