Wolves will save the world
For decades, ecologists have been interested in the idea of "trophic cascades" -- the idea that the influence of a predator at the top of the food chain has significant repercussions all the way through the plant and animal communities.
To ecologists, trophic cascades are a powerful concept. They reinforce the idea, as Barry Commoner said, that everything is connected to everything else.
The concept really excited wildlife biologists in a 1995 paper that revealed the dynamics between sea otters, kelp forests and sea urchins along the Alaskan coast. In short, if abundant sea otter ate sea urchins, kelp grew tall and thick. Without otters, sea urchins exploded and destroyed the kelp.
That very year, gray wolves were reintroduced to Yellowstone National Park. The reappearance of wolves, after their virtual extermination a century earlier, set the stage for a grand experiment. How would one of the landscape's apex predators affect large herbivores, such as bison, elk and mule deer? How would wolves affect other big predators, such as mountain lions, grizzlies and black bears? How might the presence of wolves send shockwaves through the ecosystem, affecting smaller predators such as coyotes and foxes, and even the grasses and trees on which bison grazed and deer and elk browsed?
But the situation was also a conceptual trap. As Douglas Smith, the Yellowstone wolf project leader, noted, "The danger we perceive is that all changes to [Yellowstone], now and in the future, will be attributed solely to the restoration of the wolf."
Researchers in search of trophic cascades found them. Yellowstone, it turned out, was lousy with trophic cascades.
Early research discovered that because wolves won't tolerate their smaller relatives, the number of coyotes plummeted. Researchers speculated the coyote crash might trigger a "mesopredator release,'' that is, a surge in the number of even smaller predators, such as raptors and foxes.
The proliferation of wolves, other researchers said, meant more wolf-killed carcasses for scavengers, from foxes to ravens to chickadees.
But most profoundly, the newfound presence of wolves created a "landscape of fear" among the park's big herbivores. Elk, once as docile and sluggish as zoo animals, became skittish and flighty. They no longer browsed streamside aspen and willows to nubs. The trees recovered, and stream ecosystems flourished.
Not only was all of this very interesting, but it also reinforced the value of wolves. And a lot of scientists, no matter how objective they may claim to be, like the idea of having predators around. It makes their world that much more interesting and wondrous.
Nature as Rorschach
As trophic cascade research proliferated, Mech began to keep a file of stories and research he titled "Will Wolves Save the World?"
"Because wolves have been doing so many wonderful things. It just didn't seem right," he says.
"Nature in a lot of respects is like a Rorschach test," Mech says. Researchers came to find trophic cascades, and they found them. As one critical colleague confided to Mech, "Ecologists (and particularly conservation biologists) do seem obsessed to the point of blindness with predator-induced trophic cascades.''
The complexity of nature in the rough makes it tough to parse what is really happening. In that respect, ecology and field biology are less like physics and chemistry, where experiments are easy to design (if not to execute) and more like medical research involving human subjects. Results are often murky, inconclusive and contradictory.
Subsequent research in Yellowstone has thrown a bit of cold water on the red-hot trophic cascade meme. The number of coyote packs in Yellowstone has rebounded. Mesopredators have not exploded -- not obviously, anyway. The anticipated feast from wolf kills has been tempered by the fact that the elk herd is smaller, meaning a smaller number of animals, alive or dead.
And the landscape of fear and recovery of river ecosystems? Trees aren't unequivocally recovering. And any effects of wolves are tough to separate from bad winters, drought, growing numbers of grizzlies, a long-term reduction of moose since the 1988 forest fires, and a growing season that has lengthened by nearly a month.
"How do you sort out the cause and effects?" asks Mech. In the case of Yellowstone, "the wolf is only the most dramatic factor."
Mech calls science "self-correcting." New research will clarify earlier work and correct errors, faulty assumptions and even misrepresentations. But no matter what, says Mech, "this Yellowstone trophic cascade will never die," because it has been so popularized by media and embedded in textbooks. As a result, conservationists, and even some scientists, write of wolves as though their ecological value is a given -- and in fact known.
If nothing else, the story is testament to the power of memes in science and the culture at large -- whether they involve wolves and trophic cascades, or the effect of broken windows in triggering crime, or the idea that human events unfold through the phenomenon of "tipping points." All are powerful ideas wedded to vivid images. They affect our view of the world and the very nature of inquiry.
And that is true whether we are wolf hunters, wolf lovers or concerned citizens. It is true even if we are scientists.
"Here's the thing," says Mech. "We're all human.
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