Non‐native Chinese mystery snail (Bellamya chinensis) supports consumers in urban lake food webs

Non-native species are widely regarded as threats to ecosystem structure and function; however, these species may also provide benefits to ecosystems that have lost former functions to environmental degradation. This study evaluated whether non-native species provide prey resources or induce trophic cul-de-sacs (by diverting basal energy away from higher trophic levels) in developed ecosystems where native prey are in decline. We used stable isotopes of C-13, N-15, and H-2 to assess whether non-native Chinese Mystery snail (Bellamya chinensis) provides a prey resource to consumers, and maintains the integration of benthic resources into food webs of lakes subjected to lakeshore development. Regardless of Bellamya presence, consumers in undeveloped lakes were supported primarily by benthic resources, and lakeshore development dramatically reduced consumer reliance on these resources. This was at least partly due to a reduction in the availability of native snails, a high-quality prey item, to the dominant littoral consumer, molluscivorous pumpkinseed sunfish (Lepomis gibbosus). In developed lakes with non-native Bellamya, generalist yellow perch (Perca flavescens) and piscivorous largemouth bass (Micropterus salmoides) consumed benthic resources in proportions similar to undeveloped lakes, and pumpkinseed sunfish consumed Bellamya in higher proportions than in undeveloped lakes. Thus, Bellamya provided a prey substitute in developed lakes where native snail populations were depressed; and Bellamya's influence extended to higher trophic-level consumers. Our study provides evidence that non-native species can ameliorate some effects of environmental degradation, and we suggest that future research considers how the effects of non-native species, either positive or negative, may vary across human-modified landscapes.