Native crayfish consume more non-native than native apple snails

Recent studies suggest native aquatic predators can favor native over invasive species and provide biotic resistance to invasions. The invasive apple snail, Pomacea maculata continues to spread in freshwaters of Florida and appears to be a strong competitor of the native Florida apple snail (P. paludosa). Little is known about effects of predators on either species and we compared the effects of a common native crayfish predator (Procambarus fallax) on hatchlings and juveniles. Because crayfish feed size-selectively, we predicted that the smaller P. maculata hatchlings would be more vulnerable than the hatchlings of native P. paludosa. In experimental wetland mesocosms, crayfish reduced survival of both species, but none of the P. maculata survived the 44 days exposure, such that predatory effects of crayfish were >8x stronger on the non-native P. maculata than on native P. paludosa. Crayfish in the lab selectively consumed the smaller P. maculata when offered both hatchlings simultaneously. We combined the observed survival rates with published life history data and the results (i.e., projected survivors clutch(-1)) suggested that wetlands with crayfish could have greater limiting effects on non-native P. maculata than the native P. paludosa. Wetland conditions favoring populations of native crayfish may also favor the relatively predator-resistant native P. paludosa.