Population and evolutionary dynamics in changed environments

A central focus of my current research program concerns how organisms adapt through evolutionary change to novel, stressful environments. Of course, populations are not expected to persist in stressful environments which by itself would seem to preclude adaptation to such environments. But organisms have clearly adapted, at least occasionally to novel environments. To resolve this paradoxical situation, I have been developing, in collaboration with Dr. Robert Holt, a series of mathematical models of the joint population and evolutionary dynamics of populations facing changed environments. Our research has already produced some unexpected results. First, we showed that adaptation has essentially no impact on how quickly a declining population reaches low numbers (small populations are at enormous risk of immediate chance extinction). Rather, the main effect of adaptive evolution is allow some populations (usually only large and mildly maladapted ones) to avoid reaching dangerously low numbers. Second, we have modeled the demographic and evolutionary impacts of recurrent immigration on populations that occupy stressful habitats. One surprising result is that the evolutionary spread of a locally advantageous gene in the face of a constant influx of maladaptive immigrant genes is completely independent of the rate of immigration. We are extending our analyses (1) to include stochastic components of population growth and evolutionary change, (2) to consider polygenic models, and (3) to consider adaptation in meta-populations (networks of semi-isolated stressful and benign populations). Our theoretical results point toward a vast, largely undeveloped area of empirical research: evolution in populations that seem destined for extinction. Such empirical research could provide fundamental information for understanding and predicting long-term species responses to stressful environments.

Selected publications in this research area