By CIRCulator Editorial Staff
Reprinted from: The Climate CIRCulator
FOR YEARS, scientists have been trying to figure out why many populations of pika, those tiny, cute, furry animals found in rocky slopes in the American West’s Great Basin and surrounding areas, were moving upslope to higher, cooler elevations. Since the distant relatives of rabbits perish under higher temperatures, a warming climate seemed to be an obvious culprit. The conclusion: the animals were fleeing the rising temperatures. But it turns out the answer is not so simple.
Two recent papers have tackled the pika problem from different angles. The first, led by Oregon State University author Donelle Schwalm, used species distribution models (SDMs) to understand the predicted future local changes in areas inhabited by pikas at eight National Park Service units (6 national parks and 2 national monuments) in the American West.
SDMs are widely used to understand the climatic factors controlling where different species can and cannot live, and then to project how species’ distributions will shift as the climate changes. But climate isn’t the only important factor when determining a species’ distribution. For instance, in their pika distribution research, Schwalm and colleagues included as a factor how connected each pika population’s habitat is to other suitable habitat. (Connectivity helps pikas move from large populations to smaller populations, keeping them from winking out.) The researchers also performed a series of separate calculations for the eight NPS units, recognizing that pika populations in each unit are functionally distinct.
The SDM Schwalm and colleagues employed used a total of 21 predictor variables—that is, factors that the statistical model could choose in determining what were good predictors of whether pikas would be found on a given site. While temperature and precipitation dominated the list, other factors included snow potential (since snow is essential for insulating pikas during the coldest months). Also on the list were several metrics relating to habitat. Here the researchers deduced habitat connectivity from genetic data using microsatellite DNA, the same DNA markers used to catch criminals. For the climate metrics, Parameter-elevation Relationships on Independent Slopes Model (PRISM) provided past values and Coupled Model Intercomparison Project Phase 5 (CMIP5) projections gave a range of future values.
The researchers’ results differed widely among sites. At Crater Lake National Park, climate was found to be the main driver of pika migration, with the most important climate variable for the furry critters being winter snowpack. Whereas at Craters of the Moon National Monument in Idaho, several habitat variables were found to be important for pika migration, although average July temperature was nonetheless the most important predictor. Just over the Oregon border in California at Lassen Volcanic National Monument, the researchers determined the top three predictors for pika were habitat metrics.
The second paper, led by Johanna Varner from Colorado Mesa University, notes that some pikas live in habitats very different from the typical high-elevation habitats that the species generally prefer: they also live in low elevations and mild climates. Varner and colleagues compared species inhabiting Mt. Hood, which is a typical high-elevation habitat for pikas, and the Columbia River Gorge, which is decidedly atypical for pikas. Varner and colleagues also noted big differences in behavior between the typical and atypical dwellers. For instance, Gorge pikas spent much less time storing food for winter and spent more time in nearby forests than their higher-elevation cousins. Taken together, the researchers concluded that pikas may respond to a warming climate through changes in behavior, rather than simply abandoning lower-elevation (hotter) habitats.
Schwalm, Donelle, Clinton W. Epps, Thomas J. Rodhouse, William B. Monahan, Jessica A. Castillo, Chris Ray, and Mackenzie R. Jeffress. “Habitat availability and gene flow influence diverging local population trajectories under scenarios of climate change: a place‐based approach.” Global Change Biology (2015). doi: 10.1111/gcb.13189
Varner, Johanna, Joshua J. Horns, Mallory S. Lambert, Elizabeth Westberg, James S. Ruff, Katelyn Wolfenberger, Erik A. Beever, and M. Denise Dearing. “Plastic Pikas: Behavioral flexibility in low-elevation pikas (Ochotona princeps).” Behavioural Processes (2016). DOI: 10.1016/j.beproc.2016.01.009