Predators play an important role in ecosystems, said Kauffman, and can influence plants by altering how many herbivores there are (by eating the herbivores) or by changing the behavior of herbivores (deterring them from areas where predators lurk). He adds, however, that considerable scientific debate exists regarding the importance of these two ways in which predators influence their prey. And this is especially true for large carnivores.
To complicate matters, predators use different hunting strategies there is the sit-and-wait strategy (as with a spider in a web, or a rattlesnake waiting for a mouse to leave its burrow) and the more active, go get 'em strategy (think cheetahs and wolves). "So, given that it takes a lot of energy to avoid a predator energy that could be used to stave off winter starvation we wanted to find out whether the prey of active-hunting predators such as wolves demonstrated risk-induced changes in areas where they foraged for food," Kauffman said.
To do this, the authors analyzed tree rings to discern when, in the last century, aspen stands stopped regenerating, examined whether aspen stands have begun to regenerate now that wolves have been reintroduced to the park and tested whether any differences in aspen regeneration were occurring in areas considered safe or risky for foraging elk. They used a landscape-wide risk map of elk killed by wolves over the first 10 years of wolf recovery. Finally, the authors experimentally fenced in young aspen suckers to compare the protection afforded to them by wolves versus that of a physical barrier that prevented elk browsing.
"The results were surprising and have led us to refute several previous claims regarding interactions among wolves, el
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Ecological Society of America