The introductions of non-native fish species affect the isotopic structure of recipient communities across the globe

Submitted by editor on 9 October 2015. Get the paper!

by Julien Cucherousset


Multiple anthropogenic pressures including the widespread introduction of non-native species threaten biodiversity and ecosystem functioning. Non-native species have been reported to induce ecological impacts across levels of biological organization ranging from genes to ecosystems, yet our understanding of how they affect recipient communities is still limited. Once introduced, non-native species interact with native organisms notably through competition and predation, potentially modifying the network of interactions between coexisting species and the trophic structure of recipient communities.


Here we provide a global evaluation of the impacts of non-native species on the stable isotope structure (d13C et d15N) of freshwater fish communities by comparing communities with and without non-native species. We aggregated a unique dataset gathering the stable isotope values of fish species in 496 communities located in lotic (i.e. running waters) and lentic (i.e. standing waters) ecosystems worldwide (see map, blue and green dots represent lotic and lentic ecosystems, respectively).

Using uni- and bidimensional isotopic community metrics (isotopic ranges and isotopic niche measures), we found that communities containing non-native species had a different isotopic structure than communities without non-native species. The response of communities to the presence of non-native was clearly different between lotic and lentic ecosystems and also affected by the trophic position of non-native species.


In lotic ecosystems, we observed that the introduction of non-native top predators increased the size of the isotopic niche without modifying the isotopic niche of native species. In lentic ecosystems, we found that the introduction non-native primary consumers increased food chain length. In addition, non-native secondary consumers also induced changes in the overall isotopic structure of communities and in the isotopic niche size of native species.


Although the impacts of non-native species are complex and difficult to predict, we found consistent and large scale effects that should be accounted for when investigating macro-ecological patterns of biotic interactions and community structure.