Regional versus local processes in determining zooplankton community composition of Little Rock Lake, Wisconsin, USA

The species present within a community result from a combination of local a nd regional processes. We experimentally tested the importance of these two processes for lake zooplankton communities by examining the ability of add itional species to persist when introduced into mesocosms in Little Rock La ke, Wisconsin, from other nearby lakes in the Northern Highland Lake Distri ct. We established a control treatment with only Little Rock Lake zooplankt on and two treatments that supplemented the Little Rock communities with zo oplankton from nearby lakes. Species richness declined during the 3 weeks o f the experiment so that, at the end of the third week, the treatments with added zooplankton species had the same number of species as the controls; increasing the initial number of species in the community did not increase its final species richness. A plot of the mean species richness in the loca l habitat against the mean species richness of the regional pool fell below a 1:1 slope. This suggested that local processes were more important in st ructuring Little Rock Lake zooplankton communities.