In ecological circles, a trophic cascade is a term used to describe a process in an ecosystem that starts at the top of the food chain and works its way down to the bottom. The classic example often given of a trophic cascade is what happened in Yellowstone National Park when wolves were reintroduced in 1995.
In the video below, which was produced by Sustainable Man, a website dedicated to sustainable lifestyles, this quintessential illustration of a trophic cascade is discussed.
Recently, however, some, such as Arthur Middleton, a postdoctoral fellow at the Yale School of Forestry and Environmental Studies, are challenging the way that we have thought about the wolves’ role in Yellowstone since the mid 1990s. Writing in “The Opinion Pages” of The New York Times, Middleton states that the reintroduction of wolves to Yellowstone is far more complicated and nuanced than can be explained by a trophic cascade. He argues that:
“The strongest explanation for why the wolves have made less of a difference [in Yellowstone National Park] 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 six thousand 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.”
Watch the video below, then let me know what you think. Are wolves truly the agents of a trophic cascade in Yellowstone? Or if that’s a myth, by perpetuating it, are we taking attention away from the very real conservation threats to that ecosystem?
Here’s to finding your true places and natural habitats,