Mutualisms between plants and microbes are critical for community development and ecosystem structure and function. One example of a plant-microbial mutualism is between legumes and rhizobia, whereby legumes provides photosynthate and nodule habitat to rhizobia in return for nitrogen (N) fixed by the rhizobia. For my thesis research, I am using the mutualism between white clover (Trifolium repens) and its primary rhizobial symbiont, Rhizobium leguminosarum biovar trifolii to study how urbanization affects the ecology and evolution of mutualisms.
My thesis research seeks to identify (1) the ecological consequences of urbanization on white clover-rhizobia interactions and (2) how urbanization alters GxG and GxGxE interactions between white clover and rhizobia.
Microbiomes are pervasive across the plant and animal kingdoms. For plants in particular, the microbiome is critical for community assembly and mitigation and adaptation to biotic and abiotic stress. Mounting evidence suggests that inferences about plant evolutionary history cannot be made without including the coevolution of its associated bacterial and fungal microbiome. There is also evidence that microbiome composition within a host can vary across spatial scales resulting from differential microbial community composition and environmental context.
For my thesis research, I will be sampling white clover, rhizobia, and soil along an urbanization gradient in Toronto, ON, Canada to (1) evaluate how microbiome composition varies among soil and root compartments and (2) identify the underlying drivers of microbiome assembly and composition in urban environments. I will then complement this work using a manipulative growth chamber experiment to determine how soil microbial communities alter the focal white clover-rhizobia mutualism. I contend that the actual outcome and (co)evolutionary trajectory of legume-rhizobia interactions can only be fully understood when looking at the microbiome as a whole and not as a simplfied, pairwise interaction.
A fundamental question in community ecology is: what drives community assembly? This is not an easy question to answer, as communities are the result of the dynamic interplay between local and regional factors. I am currently working with my partner and fellow researcher Kelly Murray-Stoker to address this question. We are using publicly-available data collected by the United States Environmental Protection Agency to evaluate metacommunity structure and the environmental, landscape, and network variables that best predict realized assemblages at the macroecological scale. We have found that communities can display consistent metacommunity typologies despite varying drivers of assembly. Future work will go beyond the elements of metacommunity structure and the paradigm of metacommunity typology frameworks to (1) test and compare models of community assembly (2) understand community assembly across taxonomic groups and freshwater ecosystem types at the macroecological scale.
Functional traits provide a mechanistic link between community diversity and ecosystem functioning, although the patterns and drivers of functional trait diversity are difficult to understand and model at large spatial scales. Freshwater ecosystems support a vast amount of biodiversity, but critical evaluation of functional trait structure in these systems at scales common in biogeographical research is limited. I am working with collaborators to quantify functional trait diversity of river and stream communities and to identify predictors of trait diversity across spatial scales. Additionally, I want to examine how communities and associated functional diversity respond to disturbance and environmental change at local, regional, and macroecological scales.
Niches & Community Equilibrium
Understanding and predicting community responses to environmental change are essential components of community ecology. Evaluating how community composition relates to the niche of organisms comprising the community is one way to measure the effect of environmental filtering and niche matching towards community equilibrium. Through the framework of disequilibrium theory, I am working with collaborators to (1) investigate spatial variation in environmental filtering and niche mismatch and (2) determine the underlying drivers of environmental filtering and niche mismatch. Ultimately, the goal of this project is to inform ecological theory and also conservation and restoration efforts.