Within-lake dispersal of the prosobranch snails, Viviparus ater and Potamopyrgus jenkinsi.

The gastropod species Viviparus ater and Potamopyrgus jenkinsi have both colonized Lake Zürich relatively recently. If it is assumed that they have dispersed in the Lake starting from one location, a model of random diffusion is insufficient to explain their present distribution in Lake Zürich. It is suggested that both species were dispersed by humans. In P. jenkinsi, passive dispersal by birds, fish or on floating algae may also have occurred. To estimate the rate of within-lake dispersal, life tables were constructed and the diffusivity estimated for the two species. Per capita population growth rates were calculated to be 0.00337/d for V. ater and 0.0159/d for P. jenkinsi. Diffusivity was close to 1 m2/d in both species.