Predators can benefit plants by scaring away herbivores and preventing overgrazing in a process known as a "trophic cascade." Biologists have assumed that each predator creates one kind of trophic cascade. A tiger, for example, scares herbivores away from and protects plants growing in the area it patrols. Evidence suggests, however, that not all herbivores respond uniformly to the fear of predators. Instead, in ecosystems with multiple herbivores, each one may avoid the area where it is least likely to escape the predator, and these areas might differ. If so, then predators could trigger an array of trophic cascades, benefiting plants eaten by any particular herbivore where it is most likely to be caught. To understand how a predator shields plants by scaring away herbivores, biologists must identify the area, or habitat type, where each prey species is least likely to escape. Such identification requires knowledge of prey escape tactics. The proposed research will use escape tactics of two herbivores in Washington -- mule and white-tailed deer -- to predict changes to their habitat use caused by the recent return of the gray wolf. Mule deer are slow, and use their agility to escape predators. They would be expected to shift to rough terrain where their agility is advantageous, and avoid smooth terrain where escape requires speed. White-tailed deer are fast and escape predators by sprinting away; when frightened by wolves they would be expected to avoid rugged terrain where their speed is neutralized. Consequently, wolves would be expected to protect plants eaten by mule deer that grow on gentle terrain, and plants eaten by white-tailed deer that grow on rugged terrain. This project will change the way that the ecological role of predators is understood, by highlighting the importance of prey escape behavior in driving how predators affect plants and shape ecosystems.
The broader impacts of the research include training of two doctoral students, establishment of a long-term study of the ecological impacts of wolves as a means to inform conservation policy, and initiation of an outreach program incorporating teacher training, public lectures, and video lesson plans for secondary school classrooms.
