Research:
My research interests are focused on understanding the history and evolution of tundra ecosystems. The overarching goal of my research is to determine how climate cycles of the Quaternary (the last two million years) impacted divergence and speciation in arctic and alpine tundra flora. During the Quaternary, the climate oscillated between glacial and interglacial periods, forcing populations to persist in refugia (ecologically stable areas) for extended periods of time. Given that populations of tundra plants in North America were probably isolated in multiple, geographically distinct refugia, such as the arctic tundra of Beringia and the alpine tundra of the western cordillera, it is unlikely that the disjunct populations experienced similar evolutionary histories.

In order to investigate how the diverse tundra flora was impacted by Quaternary climate cycles, my students and I are performing comparative phylogeographic analyses on multiple species of plants. The phylogeographic approach examines the contemporary geographic distribution of genetic variation within and among populations to infer the demographic history of a species and how paleoclimatic events (e.g., flooding of the Bering Land Bridge) impacted divergence. In turn, the field of comparative phylogeography attempts to infer the evolutionary history of an ecosystem by comparing genealogical estimates of history (gene trees) from multiple species, and thus provides a framework for understanding the assemblage, structure, and evolution of communities.

When evaluating the evolutionary history of distantly related, but ecologically associated taxa, analyses must accommodate the stochastic variation in genealogies due to the coalescent process and life history strategies of each species. Importantly, our coalescent approach explicitly accounts for this uncertainty and is specifically tuned to the focal taxa . In the end, we incorporate parameter estimates (such as effective population size and divergence time) from the coalescent models to test phylogeographic hypotheses developed from geologic or paleoclimatic records.