Consumer-derived subsidies may aid foundation species
Connectivity of organic matter, nutrients, and materials can be critical to the structure and function of ecosystems. Top down forcing by upper trophic-level predators can have dramatic direct and indirect effects on ecosystem connectivity. Given that many top predators are also invasive species and the frequency and extent of their invasions are increasing, their effects on the ecosystems they invade and connections with nearby ecosystems are also increasing. Here, we ask if invasive predators reduce connectivity between terrestrial and marine ecosystems using a model island-kelp forest system the Aleutian Archipelago. We address this question by comparing nitrogen stable isotope values from kelp forest primary producers and consumers at islands that differ in the amount of time that invasive foxes have been present on the islands. We estimated higher seabird densities on islands that have had invasive foxes present for shorter amounts of time. We then identified connections between seabird densities and high δ15N values in kelp forest primary producers and consumers, which is consistent with propagation of ornithogenic subsidies through the kelp forest food webs. Collectively, these findings provide novel evidence that invasive terrestrial predators reduce connectivity by obstructing the pathway for ornithogenic subsidies to travel through nearshore kelp forest ecosystems.
Gabara SS, Konar BH, Edwards MS (In review, Proceedings B) Terrestrial invasive predators reduce ornithogenic subsidies to marine forests