In 2002, Aaron Wirsing, professor in the College of Forest Resources at the University of Washington, traveled across the world to participate in a study of the effects of tiger sharks on seagrass ecosystem dynamics at Shark Bay in Western Australia. Now, as gray wolves gradually begin to re-establish themselves in the North Cascades, Professor Wirsing brings what he has learned to the Pacific Northwest.
By the 1930s, wolves were nearly eliminated from Washington state due to what Wirsing calls, “systematic persecution.” Considered a threat to livestock as well as game animals like elk, wolves were deliberately killed. But, as of July 2008, gray wolves have begun to re-establish themselves in the Pacific Northwest, which could bring about widespread changes in the ecosystem.
So why have wolves begun to return to the North Cascades?
“We don’t know, exactly, but the answer is likely that, without predator control, wolves dispersing into the North Cascades region have finally been able to survive long enough to establish packs,” said Wirsing.
Researchers like Wirsing study how the presence of predators trickles down to effect other species in the ecosystem.
“At Shark Bay, we were determining whether the presence of tiger sharks actually registers at the level of the sea grass,” explained Wirsing. “Basically, a number of large consumers, like the herbivorous dugong and the fish-eating bottlenose dolphin, adjust their feeding behavior in response to the threat posed by tiger sharks. Specifically, they forego the best feeding opportunities in order to be safe, and that frees up seagrasses and fishes from consumption. This is a large effect because tiger sharks as well as dugongs and dolphins are present during three-quarters of the year.
“In summary, the lessons from my behavioral work suggest that predators often scare their prey away from profitable feeding areas, which may allow vegetation to flourish,” said Wirsing.
Though the research conducted at Shark Bay cannot be identically applied to wolves in the Pacific Northwest, it certainly points researchers in the right direction. In the North Cascades, behavioral changes in mule deer are the focal point for researchers like Wirsing as wolves begin to return to Washington. But unlike the dugongs or the dolphins of Shark Bay, wolves present mule deer with a second predatory problem.
“Here there is already a predator on the prowl -- the mountain lion. Thus, with the return of wolves, there will be two top predators hunting the North Cascades woods, although wolves are the superior competitor,” said Wirsing.
What makes Washington’s carnivore conservation case so interesting is that wolves and mountain lions are not interchangeable, that is, they each have unique characteristics that may have a greater impact on the ecosystem when hunting the same area.
“They don’t hunt in the same way. If they did, they could be interchangeable,” explained Wirsing. “Mountain lions may already be doing enough of a job, but it is likely that the return of wolves will place additional pressure on mule deer, and other prey.
“Mountain lions are stalking predators, so they like to ambush and attack from above from steep slopes,” Wirsing said. “Wolves are coursing predators so they like running and hunt in more open areas. The danger they pose is different spatially.”
Thus, the second predatory problem facing mule deer.
“The prey can’t just avoid one area, they have two different areas they have to cope with,” Wirsing said. “It presents a whole new set of problems for the mule deer. How they cope with these problems is what we are studying before we piece together the effects of wolves.”
A similar situation was presented at Yellowstone National Park.
In 1995, wolves were reintroduced to the park, an event that brought about monumental changes to that ecosystem. The national park saw a number of changes, such as an increase in tree growth, depressed elk numbers, coyote displacement and an increase in scavengers. But unlike Yellowstone, researchers in Washington state are able to analyze the ecosystem early before wolves have been fully restored.
| “The table is set for the return of wolves,” said Wirsing. |
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“Top predators, when present, can exert positive indirect effects on plants. From what we have learned, areas where you lack top predators often experience suppression of tree growth because of unbridled herbivory and, as a result, become artificially open after a while,” said Wirsing. “If this is happening in the North Cascades, then only with the return of wolves will we expect to see normal tree sapling growth.”
The effect that a single species can have on an ecosystem is quite broad, ranging from changes in behavior patterns of prey, changes in vegetation and even an increase in competition between predators.
As his research continues, Wirsing said that he feels a growing appreciation for the role of big predators.
“I think shows like “Sustaining Our Northwest World: Carnivore Conservation in the Pacific Northwest” are vital because they truly illustrate why predators are important,” said Wirsing.
Engaging the public in the issue is crucial.
“The scientific community hasn’t properly disseminated information in the past, we just kept it within the ivory tower,” said Wirsing. “The public has an interest in knowing the facts. The strength of shows like “Carnivore Conservation in the Pacific Northwest” is that they distill a lot of research down to the essence of what it means to have a big predator in a region. My goal is to provide information and illuminate why we should conserve predators in order to really inform the debate.”
Big predators might be beneficial to the forests, but how safe are they for humans and livestock?
“Complaints often aren’t grounded in reality,” said Wirsing. “Wolves, for example, don’t have to kill many cows to engender anger and resentment in people. Thus, it is crucial to use research to establish what the threats really are because, frankly, there is not enough biology underlying opinions about predators.”
But whether people are afraid of the threat of wolves or not, the predators certainly are returning to the region.
There is currently only one known pack of wolves, but there may be more and the indication is that the number of wolves could increase quite rapidly.
“The table is set for the return of wolves,” said Wirsing.
