Competition is a fundamental driver of plant population and community dynamics, but is also strongly context-dependent. Much of my work has challenged established competition theory to better understand these dependencies, providing critical evidence for how evolutionary history, the environment, and functional similarity influence competitive outcomes. I have found that the outcome of competition will depend on the match between the competitors and their environment, the average similarity between those competitors, and the degree of functional plasticity that the competitors exhibit. I am continuing to test and refine theory in plant competition, with the long-term goal of being better able to predict competitive outcomes and the effect of competition on population dynamics and invasion. In this pursuit, I integrate information on the environment, evolutionary history, and functional traits. However, our understanding of the interrelationship between these important determinants of plant competition (and ecological function in general) is incomplete. Improving that understanding is also a long-term goal of my research program.
Plant competition
Plant-mycorrhiza interactions
Just as competition is context dependent, so are plant interactions with mycorrhizal fungi. Mycorrhizas benefit plants by increasing access to soil resources and increasing pathogen resistance, yet these benefits depend on the match between the plant, fungus, and environment. My work explores how mycorrhizas affect plant growth and reproduction across resource environments, linking these effects to conspecific density dependence, competition, and ultimately community structure. At local scales, I have found that mycorrhizas can increase plant diversity by reducing pathogen loads for rarer species, thus increasing their relative competitive abilities. This increase in competitive equivalence among species suggests that mycorrhiza effects on diversity may arise by changing coexistence mechanisms – a dynamic I intend to pursue further. At larger scales, my research has shown that mycorrhiza types can be important determinants of conspecific density dependence in temperate tree populations by determining the direction and strength of plant-soil feedbacks. However, additional variation in plant-soil feedbacks remains unexplained, potentially due to differences among species or environments. Understanding this variation may be integral to predicting how mycorrhizas affect plant populations and communities.
Community assembly and biological invasions
Species rich communities should be more resistant to invasion, especially if those communities are also functionally or phylogenetically diverse. I have found little support for this prediction across multiple ecosystems. My results suggest that the lack of relationship is, in part, because the regional processes that increase species pool sizes (and thus species richness) also increase invasibility, confounding the effect of the local community on invasion. I have developed a new integrative framework for predicting invasion by modelling phylogenetic relationships and functional traits across species pools and the local community. However, I am continuing to test and refine this method. I am also interested in the impacts of invasion and how we can predict them. I am currently developing projects to identify how invasion disrupts different plant associated interactions, which should improve our understanding of invasion effects on plant populations and communities. By developing mechanistic models of these changes, we may also be able to predict the impacts of invasion.
Although most community ecology studies measure changes in plant abundance, pollination and sexual reproduction represent an alternative pathway by which environmental change can affect plant communities that may not be immediately apparent. Numerous environmental factors have the potential to change the extent of plant reproduction as well as the recruitment of individuals into plant populations. I am currently working to isolate some of these effects and their relative importance in determining plant community responses to environmental change. This knowledge may be critical to understanding and predicting plant community responses to a changing environment. Ultimately, however, a true understanding of these interactions will require long-term research, which I intend to establish within the coming years.
The role of pollination in community assembly
(c) Jonathan Bennett 2014