Influencing the way they compete: Exotic predator mediated non-consumptive effects on two co-occurring freshwater snails.

Worldwide trade of the carnivorous snail Anentome helena may result in its chance dispersal from aquaria to the natural habitats. In course of consuming the invasive snail Physella acuta and the native snail Racesina luteola, selectively, A. helena can weaken the competitive interactions and elicit non-consumptive effects (NCEs) as well. To determine the NCEs on R. luteola and P. acuta, induced by the exotic A. helena, we observed the life-history trait variations due to competition, presence of A. helena and its cues. Since the prey snails were not exposed to such exotic predators, the resultant response will help to evaluate the prospective differences in the evasion and vulnerability of the interacting native and exotic snails. We initiated the experiment using freshly hatched R. luteola and P. acuta by placing them into intra and interspecific competitions. Furthermore, the experimental containers were divided into three treatment levels: control, presence of predator cues and A. helena. We did not find any alteration in the number of days required to attain the sexual maturity of both prey snails due to competition or predator treatments. Although R. luteola had no effects of competition; the body mass and fecundity were negatively affected by the presence of A. helena and its cues. However, the strong effect of intraspecific competition on P. acuta was weakened through increased length, body mass, and fecundity under the presence of A. helena. Therefore, the probable introduction of A. helena may indirectly affect the life-history parameters of both prey and favour P. acuta over R. luteola in the freshwater habitats of West Bengal, India. [ABSTRACT FROM AUTHOR]