Stable isotope evidence for the food web consequences of species invasionsin lakes

Species invasions pose a serious threat to biodiversity and native ecosyste ms(1,2); however, predicting and quantifying the impacts of invasive specie s has proven problematic(3-6). Here we use stable isotope ratios to documen t the food-web consequences of the invasion of two non-native predators, sm allmouth bass and rack bass, into Canadian lakes. Invaded lakes had lower l ittoral prey-fish diversity and abundance than uninvaded reference lakes. C onsistent with this difference, lake trout from invaded lakes had more nega tive delta(13)C values (-29.2 parts per thousand versus -27.4 parts per tho usand) and reduced trophic positions (3.3 versus 3.9) than those from refer ence lakes, indicating differences in food-web structure, Furthermore, a co mparison of the pre- and post-invasion food webs of two recently invaded la kes showed that invasion was followed by substantial declines in littoral p rey-fish abundance and the trophic position of lake trout, reflecting a shi ft 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 i nstance, bass-induced food-web shifts may have severe consequences for nati ve species and ecosystems.