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 and regional processes. We experimentally tested ,the importance ,of these ,two processes ,for lake zooplankton communities,by examining the ability of additional species to persist when,introduced into mesocosms in Little Rock Lake, Wisconsin, from other nearby lakes in the Northern Highland Lake District. We established a control ,treatment ,with only Little Rock Lake zooplankton ,and two treatments ,that supplemented,the Little Rock communities ,with zooplankton ,from ,nearby ,lakes. Species richness declined during 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,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 local 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 structuring Little Rock Lake zooplankton,communities.