Temperature drives asymmetric competition between alien and indigenous freshwater snails (Physa acuta vs. Physa fontinalis)
Biological invasion represent one of the major threats to global biodiversity as alien species often displace indigenous species. However, knowledge of the mechanisms behind such displacements and the driving factors of the competitive superiority of the alien species still remain rare. In our study we combined analysis of field data and laboratory experiments examining species interactions, to investigate the impact of temperature in the case of the alien freshwater snail Physa acuta that is
... ysa acuta that is held responsible for the decline of indigenous snail Physa fontinalis in Europe. From field data, we identified higher temperature as the most important difference between sites populated by alien P. acuta and those where indigenous P. fontinalis occurred. Results of the species interaction experiment conducted at 15, 20, and 25°C confirmed the hypothesis that the competitive superiority of P. acuta over P. fontinalis increases at warmer temperatures. In single species treatments, increasing temperature stimulated both species to grow faster and reach greater shell heights. Coexistence treatments revealed an asymmetric competitive interaction between the two snail species. In both species, the density of conspecifics did not affect snail growth; however, density of heterospecifics affected the growth. At 15°C, the presence of heterospecifics stimulated the growth of both species, while at higher temperatures the presence of heterospecifics stimulated the growth in P. acuta, but inhibited in P. fontinalis. Our study shows that temperature can be a powerful driver of the outcomes of alien and indigenous species' competition by driving asymmetric interaction. Further our results point up that the environmental context cannot be disregarded when investigating the interaction between alien and indigenous species, and predict alien species success and impact.