By ARTHUR MIDDLETON
The idea that wolves were saving Yellowstone’s plants seemed, at first, to make good sense. Many small-scale studies in the 1990s had shown that predators (like spiders) could benefit grasses and other plants by killing and scaring their prey (like grasshoppers). When, soon after the reintroduction of wolves to Yellowstone, there were some hints of aspen and willow regrowth, ecologists were quick to see the developments through the lens of those earlier studies. Then the media caught on, and the story blew up.
However, like all big ideas in science, this one stimulated follow-up studies, and their results have been coming in. One study published in 2010 in the journal Ecology found that aspen trees hadn’t regrown despite a 60 percent decline in elk numbers. Even in areas where wolves killed the most elk, the elk weren’t scared enough to stop eating aspens. Other studies have agreed. In my own research at the University of Wyoming, my colleagues and I closely tracked wolves and elk east of Yellowstone from 2007 to 2010, and found that elk rarely changed their feeding behavior in response to wolves.
Why aren’t elk so afraid of the big, bad wolf? Compared with other well-studied prey animals — like those grasshoppers — adult elk can be hard for their predators to find and kill. This could be for a few reasons. On the immense Yellowstone landscape, wolf-elk encounters occur less frequently than we thought. Herd living helps elk detect and respond to incoming wolves. And elk are not only much bigger than wolves, but they also kick like hell.
The strongest explanation for why the wolves have made less of a difference than we expected comes from a long-term, experimental study by a research group at Colorado State University. This study, which focused on willows, showed that the decades without wolves changed Yellowstone too much to undo. After humans exterminated wolves nearly a century ago, elk grew so abundant that they all but eliminated willow shrubs. Without willows to eat, beavers declined. Without beaver dams, fast-flowing streams cut deeper into the terrain. The water table dropped below the reach of willow roots. Now it’s too late for even high levels of wolf predation to restore the willows.
A few small patches of Yellowstone’s trees do appear to have benefited from elk declines, but wolves are not the only cause of those declines. Human hunting, growing bear numbers and severe drought have also reduced elk populations. It even appears that the loss of cutthroat trout as a food source has driven grizzly bears to kill more elk calves. Amid this clutter of ecology, there is not a clear link from wolves to plants, songbirds and beavers.
Still, the story persists. Which brings up the question: Does it actually matter if it’s not true? After all, it has bolstered the case for conserving large carnivores in Yellowstone and elsewhere, which is important not just for ecological reasons, but for ethical ones, too. It has stimulated a flagging American interest in wildlife and ecosystem conservation. Next to these benefits, the story can seem only a fib. Besides, large carnivores clearly do cause trophic cascades in other places.
But by insisting that wolves fixed a broken Yellowstone, we distract attention from the area’s many other important conservation challenges. The warmest temperatures in 6,000 years are changing forests and grasslands. Fungus and beetle infestations are causing the decline of whitebark pine. Natural gas drilling is affecting the winter ranges of migratory wildlife. To protect cattle from disease, our government agencies still kill many bison that migrate out of the park in search of food. And invasive lake trout may be wreaking more havoc on the ecosystem than was ever caused by the loss of wolves.
When we tell the wolf story, we get the Yellowstone story wrong.
Read the whole thing at: New York Times