LAUSR

Non‐native species introductions are a major concern for the conservation of natural ecosystems. The spread of non‐native species depends not only on their adaptation to the new environment, but also on the biotic features of the non‐native and resident native species and their environment that determine competition in natural habitats. There is little empirical evidence from field studies that demonstrates the existence of competition between the non‐native clam Corbicula fluminea and native freshwater mussels, and even less evidence on how global warming might affect competition and re‐shape ecological communities. In this study, field surveys within the biogeographic Atlantic region in the north west of the Iberian Peninsula found little spatial overlap between C. fluminea and the native freshwater mussel Unio delphinus. In the laboratory, intraspecific and interspecific competition between these freshwater bivalves was assessed through physiological parameters and nutritional condition in a global warming context. A significant effect for the physiological parameters and nutritional condition of intraspecific competition was found in C. fluminea, whereas asymmetric competition was evidenced between both species at greater densities of C. fluminea. Under simulated heat wave conditions, the non‐native C. fluminea was competitively superior to the native freshwater mussels when both occur together. Present findings suggest that further population declines of freshwater mussels in the Iberian Peninsula are expected under conditions of global warming, owing to competition with C. fluminea.