The impact of an invasive predator (Orconectes rusticus) on freshwater snail communities: insights on habitat-specific effects from a multilake long-term study

Abstract

Most studies of the impacts of invasive species are done at small spatial and short temporal scales, greatly limiting generalizations to natural ecosystems. In contrast, we examined the long-term, whole-lake impacts of predation by the introduced rusty crayfish ( Orconectes rusticus ) on snail communities in 10 lakes in northern Wisconsin, USA. In 1987 and 2002, crayfish and snails were surveyed in lakes that initially differed in O. rusticus abundance; during the 15 years between surveys, crayfish abundance changed substantially in four lakes. In the two lakes where O. rusticus populations increased from low to high densities, large reductions occurred in snail abundance. As predicted, snails declined much more in habitats preferred by O. rusticus (sand and cobble) than in habitats that are avoided by the crayfish (muck). In the two lakes where O. rusticus abundance decreased dramatically after 1987, no significant increase occurred in snail densities, illustrating the difference in response time of snail populations to release from predation relative to increasing predation. Contrary to prediction, no consistent difference in snail species composition existed between high and low crayfish density lakes.