Bison foraging response to the risk of wolf predation in a spatially heterogeneous winter environment: a preliminary assessment

The impact of wolves on prey populations and plant communities in Yellowstone National Park (YNP) is a central question following wolf reintroduction. Plant responses due to wolf-caused changes in the number and behavior of prey may be one of the most controversial aspects of wolf reintroduction (Smith et al. 2002). Predators are known to benefit plants due to their direct and indirect effects on prey (Werner et al. 1983; Sih et al.1985). Direct effects involve a reduction in the number of prey that feed on plants, while indirect effects involve changes in prey foraging behavior caused by the risk of predation, which is determined by predator presence and habitat characteristics (Lima and Dill 1990; Lima 1998a). Predators may have stronger effects on plants by scaring their prey than by consuming prey, because each predation event affects a single prey per unit time, while the risk of predation may cause many prey individuals to alter their foraging behavior in that same time period (Schmitz et al. 1997; Brown et al. 1999)