Competition and Coexistence

I am interested in mechanisms promoting species coexistence that are related to the competitive process. In particular, I am interested in identifying and quantifying mechanisms leading to competitive balance or equivalence among species (i.e., equalizing trade-offs). Two particular mechanisms I have been exploring are intransitive competition, whereby species compete as do strategies in the common Paper-Rock-Scissors game (collaborator: Robert Laird), and the shifting importance of density-dependence in relation to a species' position in a competitive hierarchy (collaborator: Lonnie Aarssen).

Community Assembly

I am interested in identifying and quantifying rules regarding how communities of organisms come together. I use null model analyses of community data to get at the underlying mechanisms for observed patterns. For example, it is believed that coexisting species should be relatively dis-similar from one another such that they can avoid competition (i.e., limiting similarity). I use null models to understand whether coexisting species are more different with respect to important traits, than would be expected if traits were randomly assigned to species. Using this framework, I have analyzed communities, or systems of communities of vascular plants in forests, fields, and mires, and also in communities of bird and snail species.

Quantifying Plant Competition

There exist a number of challenges in understanding both the species traits that contribute to a plant's ability to compete, and in determining how competition in species mixtures relates to the large body of existing literature that examines competition between pairs of species. I am interested in developing innovative ways of measuring competition both in glasshouse experiments, and more importantly, in natural communities. This work is directly related to my interest in understanding the influence of intransitive competition on species coexistence.

Species Size Variation

Species size distributions are positively skewed, with small species being more common and large species relatively rare. This pattern is consistent at the continental, regional, and community scale, with little variation. I am interested in understanding the forces that drive consistency in this pattern, whether they be evolutionary, or ecological in origin. In particular, I am interested in better understanding the relative contribution of species size variation to competitive interactions, and to niche separation. 

Invasive Species Biology

My interest in invasive species is anchored to my general interest in understanding why some plant species can achieve high local densities, while others cannot, independent of their native/non-native status. What is most compelling about invasive species, well at least to me, is the fact that they can achieve high local densities in non-native areas, while often not doing so in their native ranges. This strongly suggests a context-dependent community ecology. I am interested in understanding the basis for this context dependence, especially with respect to community level trait distributions.