COMPARISON OF DYNAMIC-MODELS FOR EDIBLE PHYTOPLANKTON

Alternative models for the dynamics of edible phytoplankton were compa red using long-term data from mesotrophic Paul Lake and eutrophic Lake Mendota. Alternative models fit to the data contrasted linear versus logistic algal growth, type I versus type II functional response, and prey-dependent versus ratio-dependent predation. In both lakes, the mo del with lowest prediction error had logistic algal growth and a type I, prey-dependent functional response. Under these models, the spring bloom and clear-water phase of productive lakes can be explained as an incomplete predator-prey cycle: the spring pulse of edible algae is f ollowed by a peak of zooplankton; then, edible algae are overgrazed le ading to the clear-water phase and collapse of the grazer biomass. Thi s study demonstrates the use of time series data at the ecosystem scal e to identify process-based models, contrast alternative models on a p robabilistic basis, and estimate parameters. This approach avoids the assumptions involved in extrapolating ecosystem models from smaller sc ale studies.