SOME THEORETICAL AND EMPIRICAL EXPLORATIONS OF STRUCTURE IN FOOD WEBS
Abstract
A basic unit of organization in biological systems is the ecological community. This level of organization consists of a set of coocurring species, where the population growth and interspecific interactions of one species influence the population dynamics of other species. A topic currently being debated among ecologists is how biotic and abiotic factors influence community structure. Clearly, interspecific interactions between some species are unstable, that is, the interaction cannot persist at an equilibrium level. Other patterns of interspecific interaction are stable, hence small perturbations do not destroy the equilibrium condition. Documentation of some of the mechanisms responsible for community organization is a goal of this study. I investigate community organization using both a theoretical and empirical approach. The theoretical portion of this study investigated community assembly using a Lotka-Volterra community model. The empirical portion of this study examined community assembly in highly-controlled aquatic microecosystems. Both aspects of this study examined community organization by comparing communities constructed using different colonization sequences. The general protocol was to define a species pool and create communities using different colonization pathways. In the theoretical study, colonization sequence had a substantial impact on community structure. Different colonization sequences produced different communities. The end result of community assembly was the formation of communities completely resistant to all colonization attempts. The empirical portion of this study produced surprisingly similar results. As in the theoretical study, different colonization sequences produced vastly different communities. Some assembly trajectories were resistant to colonization by consumers, while others were readily colonizable. Subtle differences in colonization sequence often determined subsequent community assembly. Historical factors, such as colonization sequence, appear to exert a strong effect on community structure. For example, I was able to construct communities (microecosystems) which converged to the same combination of producer species but supported different consumer species. Such differences appear idiosyncratic when one compares the two communities. However, with information about assembly history, the reason for such differences is clear.
Degree
Ph.D.
Subject Area
Ecology
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