9318402 Sandgren This research will provide a rigorous test of predation as a primary factor in determining prey biogeography. The PI's will test the possibility that the biogeographical distribution of many groups of algae, such as chrysophyte flagellates, is primarily the result of strong predator-prey interactions with the herbivorous zooplankton, Daphnia. There is a strong negative correlation between the distribution of Chrysophyte algae and lake productivity. While Daphnia has been identified as a dominant herbivore in lake food webs, it has not been previously emphasized as affecting the distribution of chrysophytes among lakes. Alternative hypotheses, such as competition between algae for nutrients, will be considered, as well. Predictions from these hypotheses will be test with a combination of laboratory and field experiments, modeling competition among algae species, and sampling empirical distribution of algae, Daphnia, and lake productivity. %%% This research is important because it will test a novel and important hypothesis regarding the biogeographic distribution and abundance of species in response to predator densities and habitat productivity. Because some algal blooms can cause poor water quality in reservoirs, these results will have important implications for assessing the biotic factors that contribute to lake water quality. ***
