Experimental evidence for interactive impacts of human activities on lake algal species richness

Experiments in large enclosures in a temperate lake indicate that changes in nutrient loading and herbivory, two of the most common man-induced modifications of aquatic systems, can dramatically change species richness and diversity of algae, a key component of aquatic foodwebs. Elevated nutrient loading reduces algal diversity. Herbivory decreases diversity in nutrient poor enclosures, but increases diversity in nutrient rich enclosures. That herbivores produce opposite effects on algal diversity in nutrient poor versus nutrient rich ecosystems may be the reason for the controversy regarding herbivore impacts on plant diversity. That experimentally created contrasts in nutrient loading and herbivore communities can modify a given algal diversity into the well recognized hump shaped productivity-diversity relationship demonstrates the interactive impacts of these two perturbations on algal diversity.