Multiple pathways of ecosystem regulation by the island fox, Urocyon littoralis

The impacts of omnivores on ecosystems are difficult to predict. Omnivores can impact ecosystems via potentially positive, negative, or opposing direct and indirect effects. For example, omnivores may directly decrease plant fitness via consumption, reducing growth and reproduction but they can increase plant fitness via directed seed dispersal (Tewksbury et al. 2007, Carlo et al. 2012). In addition, omnivores may indirectly increase plant fitness via the consumption of herbivores, but this interaction may not be positive for non-food plant species; herbivores may make significant nutrient contributions to an ecosystem that are lost when omnivores predate upon them (Croll et al. 2005, Maron et al. 2006).

The effects of omnivores and herbivores are mediated by rainfall and other abiotic factors (Mcnaughton 1985, McEachern et al. 2009, Levine et al. 2010). Thus, understanding and quantifying the relative importance and magnitude of the direct and indirect effects of omnivores could provide critical information in the understanding of ecosystem structure and function; understanding how these interactions are mediated by abiotic factors will enable us to predict the potential consequences of anthropogenic climate change.

Yet the dynamics of omnivore multi-trophic interactions remain understudied. To date, no studies have comprehensively examined both the direct and indirect effects of omnivores on ecosystem structure and function. In this study, I propose to examine the direct and indirect effects of the island fox (Urocyon littoralis) on the California Channel Islands ecosystem. The island fox is an endangered species that is posited to play a number of important roles as both a top predator and frugivore. I will use both empirical and modeling methods to explore how interactions among U. littoralis, small mammalian herbivores, and abiotic factors contribute to plant fitness, plant species richness, and community composition.