Animals can play key roles in freshwater ecosystems by converting food resources into waste products that affect the cycling of nutrients such as nitrogen and phosphorus. Previous research has focused on the ecological importance of dissolved wastes (e.g. ammonium and phosphate) from animals, termed excreta, because these wastes are nutrient-rich and readily bioavailable to plants and bacteria. However, animals also produce substantial amounts of particulate wastes, termed feces. For example, leaf-shredding stream invertebrates convert plant litter into fine particulate feces that can be subsequently transported downstream, broken down, or consumed by other animals. Feces may vary widely in attributes depending on diet and the source animal, suggesting species-specific roles of animal feces in larger functioning of ecosystems. In this project, researchers will explore factors influencing attributes of animal feces and compare the impact of feces on nutrient cycling to that of excreta in stream ecosystems. This project will benefit society by contributing novel information about the importance of animals in ecosystems and providing career development for multiple undergraduates and one graduate student. Results can help guide management of human activities that drive changes in animal species distribution and nutrient pollution in freshwaters.
This project will employ a combination of laboratory experiments and field surveys to assess controls, fates, and the significance of animal egesta (feces) in stream ecosystems. Dominant grazing and shredding macroinvertebrates from multiple species will be brought to the laboratory, fed diets of low or high nutrient content, and their egesta collected to characterize size and chemical binding as well as measure rates of microbial decomposition and nutrient leaching, uptake, and mineralization over the course of several months. Recurrent surveys of an Ozark headwater stream will quantify total excretion and egestion of carbon, nitrogen, and phosphorus by extant macroinvertebrates and compare these animal fluxes to background stocks and fluxes of dissolved nutrients (in the case of excreta) and fine particulate organic matter (in the case of egesta). All findings will be synthesized for modeling of how variation in background nutrient concentrations, animal community composition, and background stocks and fluxes of dissolved and particulate elements can affect the roles of animals in stream ecosystems.
