Spatiotemporal risk factors predict landscape‐scale survivorship for a northern ungulate

Abstract

AbstractEffective wildlife conservation requires decomposing the drivers of population dynamics for species affected by anthropogenic habitat alterations. Ungulates are often the focus of management actions to restore habitat and maintain connectivity as they are sensitive to landscape disturbances. We used Bayesian proportional hazards models to assess anthropogenic risk factors that could potentially predict landscape‐scale survivorship for pronghorn (Antilocapra americana) in the Northern Sagebrush Steppe ecosystem, where extensive habitat alterations occurred from the conversion of native sagebrush grasslands to agricultural lands. Using 170 adult female pronghorn monitored from 2003 to 2011, we tested the importance of linear features (road and fence densities) and forage productivity (maximum decadal normalized difference vegetation index [NDVI]) for spatiotemporal pronghorn mortality risk, while accounting for a seasonally varying proxy of snow depth. We found moderate support for the effects of linear features on mortality risk as coefficient estimates translated to predicted declines in survivorship of 27.1% over the observed range of road densities (0–1.4 km/km2) and 11.8% over the range of fence densities (0–6.1 km/km2) encountered by pronghorn. Our results also suggested that agricultural areas could act as ecological traps for pronghorn, based on mortality risk increasing by a factor of 14.3% with every 0.1 increase in maximum decadal NDVI in summer (range = 0.38–0.73). Like our previous findings, we found considerable support for the effects of average depth (in centimeters) of snow water equivalent (SWE; SWE depth = snow depth × snow density/water density) within pronghorn seasonal ranges, with mortality risk increasing by 45.7% with every 1 cm increase in SWE depth (range = 0–5.37 cm). We then developed the first broadscale, spatially explicit map of predicted annual pronghorn survivorship based on anthropogenic features and environmental gradients to identify areas for conservation and habitat restoration efforts. These efforts to highlight anthropogenic risk factors on the landscape will hopefully support conservation and habitat restoration for pronghorn populations at the northern periphery of their range.