Moving beyond resurveys of historic pika record locations: Using relict feces to test the hypothesis of climate-mediated range retreat in California

Background/Question/Methods

The American pika (Ochotona princeps) has been flagged as a bellwether of climate warming. To determine if the species has suffered climate-mediated upslope range retreat in California, researchers have resurveyed historic pika record locations. However, historic pika surveys did not attempt to capture the species’ lower elevational limit, thereby making this approach unable to falsify the hypothesis of upslope range retreat. Fortunately, an alternative approach exists—pika feces have been documented to persist for at least 36 years after site extirpation. By searching sites for both current pika occupancy and old pika feces we are able to compare the species’ current and past distribution. In 2011, I piloted this approach at 75 sites in the central and northern Sierra Nevada. 

Results/Conclusions

In most regions, I found relict pika feces at significantly lower elevations than the pikas’ apparent lower elevational limit. In the Yosemite, Desolation Wilderness, and north Lake Tahoe regions respectively, I found relict pika feces up to 320 m, 330 m, and 330 m below the lowest known current pika occupancy in that region. This evidence is suggestive of climate mediated upslope retreat but more information is needed. Further work will integrate analysis of (a) covariate dependent detection probabilities, (b) metapopulation turnover rates, (c) alternate competing hypotheses, and (d) radiocarbon isotopes to determine if feces originated before or after atmospheric nuclear testing.