Conceptual model of the hierarchical relationships among environmental parameters regulating community composition among lakes of the northern Great Plains. Salinity acts as master variable exerting direct (osmotic stress) and indirect effects (shift in predation regimes). In deep freshwater lakes, predation was likely the dominating factor for zooplankton, with production and competition having minor effects. Mesosaline lakes had low fish predation, leading to increased competition among species. In hyper-saline lakes, there was no predation and the surviving species had a monopoly over the resources; therefore, primary production was the limiting factor. Diversity deceased from freshwater to hypersaline lakes.