Trophic niche overlap between native and non-native fishes

In Mexico, non-native species are established in virtually every lake and represent one of the most important factors in species diversity loss. An iconic example is Lake Patzcuaro, which used to provide one of the most abundant fisheries of native species among freshwater systems in Mexico. But in the last decades, the relative abundance of non-native species has increased together with a reduction of native species populations. In this study, we analyze the trophic niche overlap between native and non-native species by using carbon and nitrogen stable isotopes. We did not found a spatial effect between physicochemical variables and isotopic signatures. The trophic niche area showed a small overlap among native species, but a substantial overlap of native species with non-native C. carpio and O. aureus. The non-native species P. infans presented almost no trophic overlap with other species. Non-native species have a trophic niche area two times larger than natives. The trophic niche overlap between native and non-native species was higher than among natives. The narrower trophic niche area and the high overlap with non-native species may explain the decline of native species populations. Alternative but untested explanations include altered water quality stemming from pollution and indirect effects of non-natives.