Stable isotope evidence for the food web consequences of species invasions in lakes

Species invasions pose a serious threat to biodiversity and native ecosystems(1,2); however, predicting and quantifying the impacts of invasive species has proven problematic(3-6). Here we use stable isotope ratios to document the food-web consequences of the invasion of two non-native predators, smallmouth bass and rack bass, into Canadian lakes. Invaded lakes had lower littoral prey-fish diversity and abundance than uninvaded reference lakes. Consistent with this difference, lake trout from invaded lakes had more negative delta(13)C values (-29.2 parts per thousand versus -27.4 parts per thousand) and reduced trophic positions (3.3 versus 3.9) than those from reference lakes, indicating differences in food-web structure, Furthermore, a comparison of the pre- and post-invasion food webs of two recently invaded lakes showed that invasion was followed by substantial declines in littoral prey-fish abundance and the trophic position of lake trout, reflecting a shift in the diet of lake trout towards zooplankton and reduced dependence on littoral fish. This study demonstrates the use of stable isotope techniques to detect changes in food-web structure following perturbations; in this instance, bass-induced food-web shifts may have severe consequences for native species and ecosystems.