Climate change and food webs: jackrabbits, pronghorn, and coyotes in southern Greater Yellowstone

Ekernas, Stefan

M research focused on two main objectives: identifying effects of snow depth on whitetailed jackrabbit density, and identifying the effect of jackrabbits on pronghorn fawn survival. For the first objective I measured an index of jackrabbit density using scat plots in three sites along a snowdepth gradient in the Upper Green River Basin. In addition to snowdepth, I measured vegetation and ungulate density in each of the three areas. Jackrabbit density was similar in the sites with highest and lowest snowdepth, but density was lower in the site with intermediate snowdepth. Sagebrush canopy cover and ungulate (specifically elk and deer/pronghorn) density varied along the gradient, but I found no associations between jackrabbit density and either ungulates or vegetation. Data to be collected in 2012 and 2013 will allow a more detailed investigation of the effect of snow on jackrabbits. For the second objective I measured pronghorn fawn survival in three areas with jackrabbits (the Gros Ventre Drainage and two sites in the Upper Green River Basin) and two areas without jackrabbits (Antelope Flats and Elk Ranch in Grand Teton National Park). I used fawn:doe ratios in late July and early August as an estimate of fawn survivorship, and used pellet counts in scat plots as an index of jackrabbit density. At each site I also conducted scat counts along trails as an index of coyote use. Preliminary data suggest that, as expected, fawn survival decreases with increasing coyote use. More intriguingly, my data also suggested a trend of increasing fawn survivorship as jackrabbit density increased. If this pattern holds over subsequent years of data collection, these data suggest that pronghorn fawn survival in Grand Teton National Park may be adversely affected by the functional extirpation of white-tailed jackrabbits at the site.y