| Plant community assembly is not a simple process; any factor that can affect the recruitment or coexistence of individuals can alter the outcome (e.g. nutrients, symbionts). In this thesis, I address a diverse subset of these potential factors, focusing on environmental variation, evolutionary history, competition, and pollination. I begin by testing whether evolutionary history constrains how species respond to 14 environmental factors. From this study, I conclude that evolutionary history has a weak effect on how species respond to changes in their environment, but that it can be important under certain circumstances. Next, I test whether competition is stronger when neighboring species are more related, which is hypothesized to leave a phylogenetic signature on plant communities if competition is important in community assembly. Competition did not increase with relatedness, potentially because competition was diffuse. As such, there was no measurable signature within the community. From these results, I expand existing theory to explore the conditions where competition should leave a phylogenetic signature. The importance of competition in community assembly is expected to increase or remain invariant with productivity, depending on the theory. I tested these ideas using a competition experiment with 22 species, but found competition declined with productivity, which is consistent with theories emphasizing resource supply and demand. Community assembly can also be dictated by recruitment, but few studies address how pollination, an important step in the recruitment process, varies across the community. I used a broad survey to examine whether pollination varied with environmental conditions and a manipulative experiment to test whether pollination can be predicted by abundance changes. Both flowering and flower visitation were highly dependent on environmental conditions and while they were correlated with abundance, they responded independently to environmental manipulations. This suggests that pollination and potentially seed production may become decoupled from abundance under a variety of conditions. Combined, my results suggest that many processes contribute to community assembly and that each of these processes is only important under certain conditions. More generally, my results cast doubt on the presence of general assembly rules that are applicable beyond the very smallest scales. |
