Variation in Plankton Densities Among Lakes: A Case for Ratio-Dependent Predation Models

McCauley et al. (1988) have compared the predictions of simple traditional predator-prey models with the patterns of abundance exhibited by Daphnia and its algal food supply. On one hand, the data gathered from several natural lakes of different nutrient status show a concurrent increase of phytoplankton and Daphnia biomasses. On the other hand, all models considered by McCauley et al. (1988) predict that any increase of the parameters quantifying algal productivity would lead to an increase in Daphnia biomass only. The algal biomass should not respond to a productivity increase. To resolve this contradiction, the authors suggest that enrichment affects not only algal production but also Daphnia parameters.