Nowhere to run: semi-permeable barriers affect pronghorn space use

Animal movement can mediate the ecological consequences of fragmentation; however, barriers such as fences, roads, and railways are becoming a pervasive threat to wildlife. Pronghorn (Antilocapra americana) habitat in western North America has been fragmented by roads, railways, and fences. Although pronghorn are sensitive to barriers, neither the relative permeability of different barriers to crossing nor their influence on space use have been quantified. We used a large global positioning system (GPS)-collar dataset of pronghorn (n = 1,010 animal-years) in Wyoming, USA, to first quantify the likelihood that pronghorn cross each of 5 different anthropogenic barriers, including fences, county roads, railroads, state highways, and interstate highways (i.e., interstates). Next, we assessed how each barrier influenced pronghorn space use during the winter as indexed by the area occupied, and daily displacement relative to the density of barriers on an individual's winter range. The semi-permeability of the 5 barriers varied substantially, with the interstate being the most severe barrier to pronghorn movement. Pronghorn were >300 times less likely to cross interstates compared to state highways. Although pronghorn space use was rarely influenced by barriers within individual core winter ranges, pronghorn space use was constrained by barriers on the buffered periphery of individual winter ranges. Despite their different permeability to movement, the density of fences and combined interstates and railroads had similarly negative effects on pronghorn space use. Our results illustrate that the degree to which pronghorn avoid crossing barriers may scale up to affect access to habitat. Additionally, our results indicate that the effects of barriers on habitat access are not proportional to their permeability. Our results add to a growing consensus that effective management of mobile species depends on understanding how different kinds of semi-permeable barriers influence access and use of habitats.