The Ecological Role of the Mammalian Mesocarnivore

L mammalian carnivores (species in the order Carnivora) are ecologically important because a few individuals can cause strong predation-driven direct effects or fear-driven indirect effects on communities and ecosystems (Ripple and Beschta 2004, Ray et al. 2005). Nevertheless, most carnivores are neither large nor at the apex of their ecological communities. Rather, they are small and midsized species (< 15 kilograms [kg]), often collectively termed “mesocarnivores.” Mesocarnivores far outnumber large carnivores in species richness and are much more diverse in their behavior and ecology. These species can be solitary to highly social, frugivorous to hypercarnivorous, and habitat specialists of climax communities or generalists that live in close prox imity to humans. Given their smaller size and ability to thrive in diverse habitats, mesocarnivores are usually more abundant than large carnivores, yet their impact within communities is generally assumed to be relatively minor. The grace and strength of large carnivores, and the direct threat these animals sometimes pose to humans, may inspire or, alternatively, invoke fear; at the very least, they are charismatic species that warrant our respect. In contrast, mesocarnivores are often viewed as a resource to be harvested—as vermin or agricultural pests whose impacts on human activities are to be mitigated. Further, several elegant studies of the ecological role of large carnivores have been published (e.g., Estes et al. 1998, Berger et al. 2001, Ripple and Beschta 2007), but the ecological role of the mesocarnivore has received comparatively little attention. The irony here is that although we may revere large carnivores more than the “fox in the hen house,” our collective actions are causing declines in large carnivores (Laliberte and Ripple 2004) that may often result in mesocarnivores becoming de facto apex predators (Crooks and Soulé 1999). Indeed, where large carnivores have been lost or where mesocarnivores have been introduced, there are important examples of mesocarnivores driving community structure. There are also instances in which mesocarnivores fill ecological roles, such as dispersers of seeds, that large, hypercarnivorous carnivores cannot. Collectively, these observations suggest that there is a need to assess the ecological role of mammalian carnivores other than the largest species. To establish a baseline for comparison, we first review the known trophic effects of large carnivores and then, within the context of ecological theory, present case studies revealing similar roles played by mesocarnivores in distinct ecological contexts, such as when they are apex predators in insular communities or when they have been introduced. Finally, we speculate on the potentially important but understudied ecological effects of meso carnivores on plant dispersal and disease dynamics.