NUTRIENT CYCLING BY ANIMALS IN FRESHWATER ECOSYSTEMS
▪ Abstract Animals are important in nutrient cycling in freshwater ecosystems. Via excretory processes, animals can supply nutrients (nitrogen and phosphorus) at rates comparable to major nutrient sources, and nutrient cycling by animals can support a substantial proportion of the nutrient demands of primary producers. In addition, animals may exert strong impacts on the species composition of primary producers via effects on nutrient supply rates and ratios. Animals can either recycle nutrients within a habitat, or translocate nutrients across habitats or ecosystems. Nutrient translocation by relatively large animals may be particularly important for stimulating new primary production and for increasing nutrient standing stocks in recipient habitats. Animals also have numerous indirect effects on nutrient fluxes via effects on their prey or by modification of the physical environment. Future studies must quantify how the importance of animal-mediated nutrient cycling varies among taxa and along environmental gradients such as ecosystem size and productivity.