All species are in some way confined to a certain geographic space, some span continents while others are restricted to a single mountaintop. Current ranges are a result of not only contemporary ecological conditions but also past conditions and evolutionary history. My research focuses on exploring the mechanisms creating and maintaining range limits over time.
Understanding what limits species’ geographic ranges is of importance for understanding speciation, biogeography, and conservation. There is still much we don't know about how species distributions will change with rapidly changing global climate. By understanding what limits a species current range, we can better predict how a species will fare in novel climatic conditions.
Nesting sea turtles
Nesting priority areas
Using decades of data on nesting localities and hatchling success from US National Park monitoring efforts, I am modeling current nest site preferences based on climatic conditions, beach topography, and human development. I can then project this model into the future to predict how nesting locations and densities are expected to change under different anthropogenic development, climate change, and sea level rise scenarios.
Forecasting future nest dynamics I will be using experimental and observational knowledge of sea turtle physiological requirements, phenology, and environmental pressures to create a multi-level Bayesian model that allows me to incorporate changes to the landscape and climate with known species-specific biology that can be be applied in a spatial context with strong predictive power. This model leverages over a decade of nest inventory data from across the nesting grounds of loggerhead and green sea turtles, to predict how trade-offs in inundation and depredation risk influence nesting success and vary across the nesting beach landscape now and in the future.
Plethodon salamanders
I focused my graduate research on montane terrestrial salamanders in the genus Plethodon in the Ouachita and Appalachian Mountains. The climatic sensitivity of montane salamanders and location of a biodiversity hotspot in the southeastern US make them an ideal study system for testing hypotheses on species’ distributions. By focusing on mountaintop species, I was able to look at repeat environmental gradients in small geographic areas, combining molecular, physiological, and spatial data to develop a more complete understanding of current and future distributions for potentially imperiled species.
Niche modeling for species in the Southern Appalachians
Niche modeling is valuable tool for not only examining species’ current biogeography, but also for anticipating where populations and species will be able to persist under rapid climate change. The most widely used methods for forecasting species range shifts do not often take into account the organism’s biology and may present too simplified of a picture for how animals, especially montane restricted species will adjust to changing global environmental conditions.
I compared the current and future forecasted distributions of four species of Plethodon in the Southern Appalachians using both a traditional correlative model approach (Maxent) and a biophysical model that uses species specific equations and parameters to model annual energy budget in terms of energetic inputs through foraging and outputs through growth, maintenance, and reproduction. Prior research projecting future distributions under climate change using Maxent predicts a very dire future for montane endemic salamanders in the Appalachians. My findings indicate that correlative models may be over predicting range loss as a result of non-analog future climates, an issue that biophysical models overcome.
Taking a mass measurement
and tail tip in the field
Gene flow in complex landscapes
Gene flow has the potential to aid local adaptation at the range edge through the introduction of genetic diversity, however it can also have a swamping effect reducing local adaptation through the influx of maladaptive alleles. How genetic information moves across the landscape and the consequences of this movement is still unclear. In collaboration with Donald Shepard (University of Central Arkansas), I am using tissues collected from elevational transects to quantify historic migration rates between mountaintop and lower elevation populations on three mountains in Oklahoma. These measurements will be used with local adaptation data to see how gene flow potentially impacts adaptation at the range edge. To understand what habitat factors influence movements across an entire mountain I will be employing landscape genetics to test resistance surfaces made from GIS layers.
Closed system respirometry
Local adaptation to abiotic conditions
Whether populations have the ability to adapt to differing climatic conditions is important for not only interpreting current range limits, but also for predicting how species will fare in a changing global climate. To assess local adaptation in a skin-breathing, temperature sensitive amphibian, I have been measuring metabolic rate at a gradient of naturally occurring temperatures to quantify metabolic thermal sensitivity for populations from differing climatic environments for both Plethodon ouachitae and co-occurring Plethodon kiamichi.
3D scan of a Plethodon
Influence of biotic interactions
Species interact with other species, often through predation, parasitism, or competition. Montane specialists, like Plethodon ouachitae, are frequently replaced at low elevation by closely related generalist species. P. ouachitae inhabits six mountaintops, on four of those mountains it is replaced at low elevation by Plethodon albagula, on the other two mountains it co-occurs with a different large, generalist plethodontid, P. kiamichi. Based on prior work conducted by Carl Anthony et al.,P. ouachitae that occur in allopatry appear to use a highly aggressive strategy to displace both con and heterospecifics.
University of Minnesota undergraduate Camille Herteux is completed aggression trials using P. ouachitae from populations on mountains where they co-occur with P. kiamichi and where they exclude P. albagula. Pairing P. ouachitae with conspecifics from all mountains and heterospecific P. kiamichi to assess how agonistic behavior varies with sympatry.
I have worked with University of Minnesota undergraduate Jonathan Keller to examine the underlying morphology contributing to competitive interactions and possibly aggressive interference. Using the University of Minnesota’s X-ray Computed Tomography lab, we have been creating three-dimensional images of salamander skulls for individuals across the elevational and geographic range of P. ouachitae. We will be using these scans in geometric morphometric analyses to test hypotheses of whether a shift in jaw shape corresponds to aggressive behavior and/or species coexistence.