Beyond biodiversity: The impact of food web structure on ecological stability

Massive changes to the world's ecosystem are resulting in a deterioration of biostructure---the complex web of species interactions that make up ecological communities. Therefore, it is of major interest to ecologists to uncover the biological mechanisms that govern how biostructure impacts important ecosystem attributes. A major focus has been on understanding the relationship between biostructure and ecological stability. Stability is an important trait as stable systems are less temporally variable, possess populations with densities well bounded away from zero, are resilient, and are resistant to perturbations. Using a combination of ecological experiments, theory and the analysis of comparative data sets, I demonstrate how various food web structures seen in nature are critical for stability. In many of these structures, stability arises from asynchrony occurring at a variety of levels. In Chapter I, I use experimental aquatic microcosms containing competing single-celled microorganisms to test the portfolio effect. I show that environmental variation and community composition interact to influence population and community stability. Asynchrony among the population dynamics of competing species increased stability. In Chapter II, using rotifer-algae aquatic microcosms with multiple trophic levels, I show that weak interactions coupled to strong interactions by generalist consumers dampen strong interaction strengths and increase community stability. Stability arises from asynchrony between resource populations generated by the generalist. Increasing in scope to ecosystems, in Chapter III, I unfold the dynamical consequences of detritus-based nutrient recycling on the stability of ecosystems. Using ecological theory I show that detritus drives asynchrony between resources and the nutrients they require for growth, increasing stability. Finally, in Chapter IV, I synthesize ecological theory with the analysis of multiple data sets, to compare stability differences in aquatic and terrestrial ecosystems. In support of theoretical predictions, I show that differences in the attributes of these ecosystems lead to increased energy flows within aquatic ecosystems, making them less stable than terrestrial ecosystems. At a variety of scales from populations to ecosystems, I show how interactions between species have important consequences for the stability of larger communities and ecosystems.