SEFS Alumnus Aaron Johnston Awarded Mendenhall Fellowship

Aaron Johnston, who earned his Ph.D. from SEFS in spring 2013, was recently awarded a prestigious, two-year postdoctoral research position with the U.S Geological Survey’s Mendenhall Research Fellowship Program! Johnston studied competition between eastern and western gray squirrels in the Puget Sound lowlands for his dissertation (working with Professor Emeritus Steve West), and he will be moving to Bozeman, Mont., after the winter holidays to begin the fellowship.

Aaron Johnston

Aaron Johnston’s fellowship will include two field seasons, and he’ll be expected to produce several publications from the research.

Selected through a competitive proposal process, Mendenhall Fellows help USGS staff conduct concentrated research around a number of important areas. Johnston’s proposal, “Extinction dynamics and microrefugia of the American pika,” will pair him with Dr. Erik Beever in Bozeman to explore the effects of climate change on pikas in the Cascades and Northern Rockies, though he hasn’t finalized his study area yet. He’ll have a research budget and be able to bring on a couple assistants to help with the project.

American pikas (Ochotona princeps) are a smaller relative of rabbits and hares. They’re an herbivorous alpine species that spread south with the last ice age, and now they’re holding on in high-altitude mountain areas in western North America. Their dependence on colder temperatures and preferred habitat—talus fields and rock piles at or above the tree line—has generally restricted their range to “sky islands” at the tops of mountains, where movement from one region to another can’t happen quickly, if at all. As a result, a warming climate threatens to shrink or eliminate the habitable range of pikas in the coming decades, and some estimates already suggest that 40 percent of American pikas in the Great Basin have disappeared in the last century, with the remaining populations retreating to even higher elevations.

Aaron Johnston

With their habitat shrinking as the climate warms, American pikas are retreating to higher elevations on the “sky islands” of mountaintops.

Johnston says there are competing hypotheses about why this large-scale extinction is occurring. One widely supported theory revolves around the fact that pikas can’t survive prolonged exposure to high temperatures (more than a couple hours above 80 degrees, in fact, can kill them). Yet in a few regions, where temperatures far exceed that maximum—such as Craters of the Moon and Lava Beds national monuments—some pika populations have found a way to survive using microrefugia to escape the heat. Other hypotheses focus on phenology, and whether changing temperatures will reduce available vegetation for pikas, or if warmer winters will reduce available snowpack for insulation and expose pikas to extreme cold.

To address these questions and help design effective conservation strategies, Johnston’s project will involve modeling and mapping pika habitat topography using LiDAR. He’s been working in Professor Monika Moskal’s Remote Sensing and Geospatial Analysis Lab, and he sees powerful applications of LiDAR for wildlife management. “I think it’s a really exciting new technology that has enormous potential we’re just starting to realize,” says Johnston.

Project Summary
The objectives of this study are to:

1. Develop broad-scale maps of talus at high-resolution through fusion of LiDAR and multispectral imagery;
2. Develop predictor variables for untested hypotheses about substrate, snowpack and phenology;
3. Evaluate regional variation in extinction mechanisms by incorporating new data on extirpations outside of the Great Basin; and
4. Evaluate differences in habitat and connectivity maps created by models with and without microclimate and microhabitat variables.

This project will use limited field work to characterize substrate at selected sites for development of talus maps, and supplement existing data on pika persistence at historical sites of occurrence. Results of this study will increase understanding of pika responses to climate change, inform conservation strategies, and provide map products widely applicable to many research areas, including wildlife ecology, plant ecology, geomorphology, hazard assessment and hydrology.


Congratulations, Aaron, and good luck with this tremendous opportunity!

Photo of Johnston © Aaron Johnston; photo of pika © Justin Johnsen.

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