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 localand regional processes. We experimentally tested the importance of thesetwo processes for lake zooplankton communities by examining the ability ofadditional species to persist when introduced into mesocosms in Little RockLake, Wisconsin, from other nearby lakes in the Northern Highland LakeDistrict. We established a control treatment with only Little Rock Lakezooplankton and two treatments that supplemented the Little Rockcommunities with zooplankton from nearby lakes. Species richness declinedduring the 3 weeks of the experiment so that, at the end of the third week,the treatments with added zooplankton species had the same number ofspecies as the controls; increasing the initial number of species in thecommunity did not increase its final species richness. A plot of the meanspecies richness in the local habitat against the mean species richness ofthe regional pool fell below a 1:1 slope. This suggested that localprocesses were more important in structuring Little Rock Lake zooplanktoncommunities.