| A general, widely accepted framework for the assembly of ecological communities, including the processes that determine both the number and identity of coexisting species, has yet to be developed in ecology, despite decades of effort stemming primarily from the seminal works of Hutchinson and MacArthur and despite its significance to both basic science and conservation applications. The current debate surrounding this topic is centered on the primacy of deterministic, niche-based processes, particularly interspecific competition, versus stochastic, species neutral processes, as elucidated by S. Hubbell. Here I utilize data from J. H. Brown's long-term study on desert rodent communities near Portal, Arizona, to gain insight into the roles of stochastic and deterministic processes in the structure and assembly of this community.;First, I assess changes in the shape of the rank abundance distribution (RAD), an index of how species divide available resources, through time in this desert rodent community. Because energy use may be more appropriate for studying resource division than abundance, I also evaluate an energetic equivalent of the RAD. Significant, directional trends in the shapes of both distributions are present in this community.;Second, I further explore the role of resource limitation on ecological communities, which is known to restrict the total abundance, biomass, and community energy flux a given community can support. I, along with my coauthors, present a simple framework that links abundance and biomass with an energetic constraint and test the resulting predictions using the Portal rodent community. The average body size of an individual in this changing community has decreased by almost 50% and average abundance has doubled, supporting the tradeoffs predicted by the framework. These results lend support to the idea of resource limitation on desert rodent communities and demonstrate that systems are able to maintain community energy flux in the face of environmental change, through changes in composition and structure.;Lastly, to further understand these demonstrated shifts in the structure and composition of this community and thereby elucidate mechanisms of assembly, I examine the impact of an extreme climatic event on the relative abundances of particular species. I show that differential mortality in the dominant species provided a resource opportunity for a recently colonizing species, which expanded its population, rapidly reaching record high abundances and depressing populations of the former dominants. (Abstract shortened by UMI.)... |
