Testing ecological and evolutionary hypotheses for geographic range limits

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Understanding species' geographic distributions is a central goal in ecology and has emerged as a pressing scientific need as we strive to address the effects of climate change on biodiversity. Towards this end, my research focuses on understanding the ecological and evolutionary drivers of species' range limits. My past work has demonstrated that range limits often closely align with the limits of suitable habitat for species. Yet, departures from this pattern, as well as numerous cases whereby species have failed to track climate change, highlight the need to further probe the ecological factors influencing range limits. Furthermore, explaining range limits ultimately requires determining why adaptation fails at the edge of the range. These needs motive three short-term objectives: 1. Explain variation in the extent to which species occupy their potential range. Whether range limits reflect the limits of suitable habitat or constraints on dispersal may depend on features of the landscape and on species traits. My lab will use spatial data to model suitable habitat and the potential ranges of ten amphibian species. Using these models, we will test whether the steepness of environmental gradients, the dispersal capabilities of species, and/or local colonization and extinction dynamics influence the extent to which species fill their potential ranges in different places. 2. Evaluate the effects of species interactions at range limits. The importance of species interactions to range limits is highly debated. Furthermore, there are conflicting ideas as to whether species interactions are more or less impactful when abiotic conditions are stressful. My lab will use eDNA to quantify changes in the frequency of species interactions towards the low elevation, putatively benign, range limits of three amphibians and will experimentally test whether the effects of these interactions on each species varies across abiotic conditions associated with high versus low elevation limits. 3. Test genetic constraints on adaptation at the edge of the range. Both the random loss of genetic variation and the movement of genetic variants between sites following dispersal may influence genetic diversity at range limits and thus the adaptive potential of peripheral populations. My lab will use genomic data to quantify genetic variation and population connectivity at the edge of the range of the long-toed salamander. We will then test whether the extent to which populations demonstrate genomic signatures of maladaptation predicts field-based measurements of individual performance. Apart from enriching our understanding of species' range limits, this research will provide advanced skills training for 5 graduate and >5 undergraduate students. The skills and knowledge gained by students will equip them for a variety of careers and allow them to make meaningful contributions to scientific discovery and application.