Food web theory predicts a series of relationships between the species richness (number of species) of a natural assemblage and the stability of species abundances in time. In spite of the importance of food web dynamics to both basic and applied issues in ecology, few of these predictions have been tested experimentally. This project will first assemble replicated food webs of protozoans that differ in species richness, connectance (number of species interactions in an assemblage) or number of trophic levels. These webs will then be used to evaluate the persistence and temporal stability of communities with and without small perturbations in nutrient levels. These enrichment experiments are very important to improve the knowledge base of fertilization effects in nature, an area of great concern as a result of the nutrient loading associated with global change. In another set of experiments, the effects of species richness will be determined in the laboratory relative to the persistence and variability of species. A final group of trials will examine whether the degree of connectance in food webs affects their stability, and whether stability decreases as food chains increase in length. Although these experiments will be done on assembled communities in the laboratory, ancillary studies will employ similar approaches to explore whether natural protozoan communities collected from the field will perform similarly to those constructed artificially.
