Walleye Foraging Ecology in an Interconnected Chain of Lakes Influenced by Nonnative Species

The Laurentian Great Lakes are a source of nonnative species for smaller inland lakes throughout the region; however, the foraging ecology of predators in smaller systems invaded by nonnative species has not been well studied. We used diet and stable isotope analyses to describe the contributions of native and nonnative forage species to the diets of Walleyes Sander vitreus within an inland lake chain invaded by multiple nonnative species. Our hypothesis was that the Walleyes' diet would be associated with the relative amount of prey available in littoral or offshore-pelagic habitats and would ultimately be linked to the dominant habitat type. We found that Walleyes in the study lakes exhibited flexibility in their dietary inclusion of nonnative prey species. Similar to predators in the Laurentian Great Lakes, Walleyes in smaller inland lakes integrated littoral nonnative species into their diets. However, Walleyes unexpectedly showed limited usage of accessible nonnative pelagic forage. We suggest that predator responses to species introductions are likely context dependent and warrant further investigation in multiple systems and with multiple predators to determine the full extent of nonnative species' integration into the food web and their influence on native populations.