Testing patterns of species richness: A study of experimental and natural prairie plant communities

My advisor has described ecology as "the scientific study of the causes of pattern in the biological world." As a student of ecology, I became interested in patterns of species richness in biological communities. These patterns are interesting because they suggest that species assemblages are not just the result of individual population dynamics but also result from predictable properties or rules that govern these assemblages.; The focus of my thesis was two-fold. First, I wanted to test whether species richness patterns observed in natural systems could be replicated in an experimental system. Second, I wanted to test some of the hypotheses that have been proposed to explain these patterns. Because of the proximity and availability of Minnesota tallgrass prairie plant species, I based my study on this type of community.; There were two patterns of plant species richness that I was particularly interested in. These were the unimodal relationship between plant species richness and disturbance, and the unimodal relationship between plant species richness and plant productivity. These two relationships are explored in Chapters 1 and 2 The following three chapters are related in one way or another to testing mechanisms or consequences of the species richness-productivity relationship.; In general, I found that my experimental communities did not produce expected species richness patterns. However, these communities did produce other patterns that revealed both the importance of community components (the types of strategies encompassed by the plant assemblage) and the presence of community properties (e.g. constraints placed on species richness by disturbance-caused extinction, effective area, and nutrient enrichment) as well as the negligible effect of competitive exclusion in situations where it was expected. In the penultimate chapter, I discuss other, non-experimental, dynamics that were generated by these communities and in the final chapter I show how species richness-productivity patterns can be obscured in "natural" systems.