Lake characteristics drive concordant trophic responses across ecosystems in three top predator fish species

Understanding similarities in trophic ecology of top predators is crucial given their influences on food webs. We sampled walleye (Sander vitreus), northern pike (Esox lucius), and muskellunge (Esox masquinongy) from 17 Minnesota (USA) lakes and used δ13C and δ15N to estimate littoral carbon use, trophic position, and isotopic niche size of each species. All three species showed large inter-lake variability yet had concordant trophic responses across lakes, as littoral carbon use, trophic position, variability in littoral carbon and trophic position, and niche size were all positively related among species across lakes. Concordant responses were driven by a few key lake variables, with trophic position positively related to proportion littoral area and depth of hypoxic water, littoral carbon positively related to depth of hypoxic water and presence of zebra mussels (Dreissena polymorpha), and niche size inversely related to lake area. Our results indicate lake characteristics may influence food webs via consistent effects on multiple top predators. They also show that the amount of suitable habitat can be important for the ecosystem size hypothesis for trophic position.