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Abstract
Understanding how plant species coexist and interact with their biotic and abiotic environment remains a key goal of community ecology. A growing knowledge of plant functional traits has led to their increasing use in studies of community assembly. This dissertation addresses questions of trait evolution and community assembly from both theoretical and empirical perspectives. Using simulations, I explored the interacting impacts of species richness, habitat heterogeneity, multiple, linked traits, and varying levels of dispersal limitation on trait evolution and species persistence in an ecological community. Fine-scale habitat heterogeneity led to broad ecological equivalence and long-term species persistence, while the outcome of simulations with coarse-scale heterogeneity depended on other factors. These findings differ substantially from prior work, likely because we implemented the unique combination of spatially explicit interactions along with using a genetical model of trait evolution. Most current work studies considering community assembly from the perspective of functional traits have been based on species mean trait values, minimizing the importance of intraspecific variation. In this study, I examined the structure of a temperate forest in detail with relation to five leaf functional traits. There is a strong intraspecific plastic response to light availability in these traits, as well as substantial unexplained intraspecific and even within individual variation. This broad range of intraspecific trait values translates to strong interspecific overlap in trait values, suggesting most of the tree species within the studied forest share a common strategy with respect to these leaf functional traits. These results also call attention to the importance of considering individual-level variation in studies of community ecology. When these same traits are considered in a spatially explicit manner, there is some evidence supporting clustering of individuals with more similar traits than expected by chance, as well as many traits that appear randomly placed across the landscape. Combining the major temperate forest dataset with more limited data from a tropical forest, I attempted to address competing hypotheses of niche breadth and overlap in relation to the latitudinal gradient in species diversity. While data continues to be collected on this part of the project, initial analysis of the data suggests that some traits behave differently in the species-rich tropical forest than in the temperate system, but overall, niche breadth seems to be similar in the two systems.