Jonathan Richardson Hometown: Mukilteo, WA Advisor: David Skelly

For amphibian population declines in the U.S., habitat loss and fragmentation appear to be the leading attributed causes. The life history and population ecology of pond-breeding amphibians may leave them particularly sensitive to the increasing levels of human-mediated landscape alteration and habitat fragmentation. Often characterized as metapopulation systems, dispersal is thought to be a necessary link between amphibian populations that must exchange individuals in order to persist over long time spans. However, there are two competing perspectives dealing with population connectivity.

Ecologists and conservation biologists have focused on the positive effects of connectivity on population persistence, asserting that interactions between populations can provide demographic and genetic rescue effects. Conversely, evolutionary biologists have highlighted the potential negative effects of population connectivity and corresponding gene flow on patterns of local adaptation among populations experiencing divergent selection pressures. While the ecological perspective has long dominated population ecology, recent research is shedding light on the importance of adaptive evolution on ecologically relevant time scales. While both ecological and evolutionary theories have embraced spatial perspectives, considering the same process they have reached disparate conclusions about the role of dispersal on the fate of populations.

For my dissertation research, I propose to explore the nexus between these two perspectives using populations of two pond-breeding amphibian species endemic to New England. I will assess the influence of different types of landscape structure and levels of habitat connectivity on local and regional population dynamics of spotted salamander (Ambystoma maculatum) and wood frog (Rana sylvatica) populations inhabiting the basalt ridge of Connecticut. Specifically, I will study how different levels of habitat connectivity influence gene flow, and how, in turn, this gene flow effects population persistence and dynamics in terms of pond occupancy, population densities, and local adaptive traits specific to each sub-population.

I propose to use an approach that simultaneously considers ecological and evolutionary consequences of movement to evaluate amphibian populations across a spectrum of connectivity. Ultimately, this research may refine our understanding of how human disturbance affects patterns of evolution and persistence of populations, an issue critically important to current conservation initiatives.