research interests
My research investigates the environmental, ecological, and evolutionary forces that influence speciation. It evaluates the relative contributions of microevolutionary and abiotic processes in promoting the divergence of populations, under the assumption that population divergence is often the initial phase of speciation. From the perspective of population genetics, this could be described as an exploration of the factors that influence the formation of population genetic structure, while a phylogenetic perspective might include an estimate of the relationships among the populations. From either viewpoint, a model of the historical divergence of populations provides a context for understanding how evolutionary forces that act within or between populations (e.g., selection, drift, gene flow) ultimately produce macro-evolutionary patterns. In the next several years, my research will be devoted to investigating speciation and population divergence in dynamic natural systems, as well as to improving the methodological approaches used in these investigations.
My dissertation research consisted of a comparative phylogeography project that explored the evolutionary history of species inhabiting the mesic forests of the Pacific Northwest. Genetic patterns in diverse organisms such as willows and salamanders can be difficult to compare using qualitative approaches, so this work utilized an explicit hypothesis-testing approach that provided a metric for comparison among codistributed species with disparate life-history traits. Results identified two phylogeographic patterns in these species, suggesting that sets of species respond to environment change in similar ways. One concept that follows from this work is that of the evolutionary cohort, species which exhibit broad similarities in population genetic structure because they responded in similar ways to environment change.
Comparative phylogeographic studies interpret genetic concordance among codistributed species as evidence that the population genetic structure in each species has formed in response to shared environmental events. Implicit in this interpretation is the assumption that species which are currently codistributed would have been similarly codistributed in the past, but this assumption is rarely tested. Since the ancestral distribution provides a key piece of evidence towards identifying the causes of phylogeographic incongruence, I have incorporated GIS-based paleodistributional modeling to estimate the possible ancestral distributions of focal species during the last glacial maximum. This novel perspective can be integrated with genetic data through the use of models of population history and parametric simulations.
