Isotopes suggest trophic differences between alien Radix auricularia (Linnaeus, 1758) (Lymnaeidae) and sympatric endemic gastropods in Lake Baikal

In recent decades, the Eurasian native and invasive gastropod Radix auricularia has been found widely dispersed in the endemic communities of Lake Baikal. A comparative analysis of stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes in the foot tissues of individuals of this species and endemics with similar shell sizes, filter-feeding Parabaikalia florii (Baicaliidae) and grazer-scraper Benedictia baicalensis (Benedictiidae), was carried out to identify possible competition for food resources between the three coexisting species. Despite the similarity of the δ¹⁵N values (P = 0.37), R. auricularia and P. florii have non-overlapping isotopic niches (P = 0.001), assimilating different components of phytonutrients. Radix auricularia and B. baicalensis differed in the δ¹⁵N values (P = 0.001) with a significant overlap of the isotopic niches (P = 0.66) due to the ability of the latter to consume food of animal origin. We additionally discuss the disparities and similarities of the basic components in the food boluses of the alien and endemic species.