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The importance of being scary

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Through the pairing of snowshoe hare and lynx, biologist Aaron Wirsing studies the science of predators and prey: an interview conducted by communications intern Grant Wilson.

This article originally appeared in fall 2009 Conservation Northwest Quarterly. It was written by communications intern Grant Wilson.

Aaron Wirsing, with snowshoe hare, on Lolo Pass in Idaho. Photo by Todd SteuryLet’s face it: An empty-bellied Canada lynx gracefully lunging at a snowshoe hare is quite the spectacle. In fact, these chase-capture-kill sequences are what first sparked the fascination of biologist Aaron Wirsing, assistant professor at the University of Washington’s School of Forest Resources. According to Dr. Wirsing, the relationship between predator and prey has vast ecological implications. “Predators have two roles: as an agent of mortality and an agent of intimidation,” said Wirsing. “The focus of my research is on the latter role—how prey animals cope with the prospect of being eaten, which is important because animals change their behavior in order to be safe.”

Wirsing began studying the behavior of animals in response to fear, known as “risk effects,” in Australia’s lively Shark Bay. According to his research, tiger sharks have a vast ecological effect in this area by influencing the foraging habits of other species, such as dugongs (sea cows) and sea turtles. As shark populations around the globe dwindle, so does the fear that their presence invokes in their prey, prompting, for example, lumpish dugongs to sometimes overgraze seagrass areas to the detriment of the ecosystem and its residents (including themselves!).

Interestingly, Aaron Wirsing’s research has shown profound similarities between Shark Bay and the Pacific Northwest in prey’s behavioral responses to predators. Consider wolves and ungulates (hoofed mammals, like deer), for example. According to Wirsing, “both dugongs and ungulates alter their foraging behavior in order to gain safety from predators—tiger sharks and wolves, respectively—and, in doing so, free plants from herbivory. In other words, tiger sharks and wolves may benefit plants by scaring off large herbivores.” Often times it is riparian zones and other sensitive areas, where certain ungulates tend to forage when unchecked by wolves, that are the major benefactors of this phenomenon.

Washington’s gray wolf population, now reestablishing itself after roughly 80 years of absence from the state, also happens to be a particularly valuable research subject. “Because wolves have not colonized the whole area,” explained Wirsing, “there is a natural scientific control for deer habitat use.” This means that the foraging habits of ungulates in areas where wolves are present can be compared with wolf-free areas as a means of pinpointing with greater certainty the effects of fear in ungulates.

Another predator-prey interaction that Wirsing researches is that between snowshoe hares and Canada lynx, “specialist predators” whose diet consists almost entirely of snowshoe hares. The lynx’s habitat currently ranges from the North Cascades east to the Columbia Highlands, but there is talk of perhaps an eventual reintroduction to some areas of their historic habitat, such as the Kettle Range, as part of a recovery strategy for Washington’s rarest cat.

The behavior of snowshoe hares, and their resulting availability to lynx, is crucial to the longevity of lynx. However, there appears to be some behavioral anomalies from a variety of possible sources that threaten this predator-prey relationship. For example, fragmented landscapes and open clearcuts may be disruptive to much snowshoe hare behavior because they typically avoid predation in thick forage. “Does carving up the landscape influence vulnerability of hares to lynx?” Wirsing queries.

The pervasive pressures of climate change complicate matters further. He says that reduced snowpack resulting from climate change could make hares more vulnerable to lynx, for example if hares remain white long past the time of snow cover and thereby allow for heightened lynx hunting success. “Yet, ultimately.” says Wirsing, “I suspect that climate change will prove harmful to both lynx and hares by allowing for intrusion by other predators like coyotes and bobcats. As snow recedes, these predators can be expected to move in, displace lynx, and prey heavily on hares, ultimately leading to a system with few lynx and smaller hare populations subject to heavy predation by carnivores that were excluded by deep snow.”

Aaron Wirsing, unmoved by the thrashing snow and rugged terrain of the Loomis backcountry—an important area where lynx and snowshoe hare reside—plans to investigate these imperative issues in the coming months.

In the meantime, if you happen to spot from afar a wolf or another apex predator properly performing its ecological duties of frightening its prey, tip your hat and say, “Thanks for being so scary!”

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