Why Predators Matter
Posted by Richard Conniff on December 22, 2015
There are no doubt plenty of contenders in the category “most destructive thing humans have done to Planet Earth,” but killing off predators has to rank near the top. And it is a continuing crime against nature.
Looking just at modern times, the list of predators we have driven to extinction includes North Africa’s Atlas bear, North America’s short-faced brown bear, the Caspian tiger, the thylacine (a marsupial carnivore in Tasmania), and the Zanzibar leopard, eradicated in the 1990s because of nonsense folklore about witchcraft.
We have pushed the few remaining big predators into a sad vestige of their old territory. Leopards are now gone from 66 percent of their range in Africa and 85 percent in Eurasia. Tigers are down to just seven percent of the territory they once ruled. African lion are on the brink of extinction in the wild, with just eight percent of their former range. Gray wolves, exterminated from the entire United States except Minnesota and Alaska, have in recent decades managed to slip back into a half-dozen or so other states, but only against the most violent resistance.
Why are we so terrified of predators? We are haunted by the ghosts of our evolutionary history, much as are pronghorn deer. They evolved to outrun North American cheetahs—and still run that fast even though the cheetahs went extinct 12,000 years ago. You might imagine that humans would be smarter than that, and yet we continue to run from our entire history with predators, and that of our primate ancestors. That is, our history as dinner. We have served in that capacity for lions, leopards, tigers, crocodiles, snakes, saber-toothed cats, sharks, and an ungodly assortment of other predators. Is it any wonder that predators still make us twitch?
On top of fear, add the illusion of economic interest. Ranchers rage that predators kill their livestock. But the reality is that they hate them with an irrational intensity basically because their daddies always did. Cattle die far more often from bellyaches or bad weather. Predators ranked just seventh among causes of death in this USDA study. But it’s easier for ranchers to take out their frustrations on the predators. Economic interest has also shaped the approach taken by many state Fish and Wildlife agencies: Their budgets come largely from hunting and fishing fees. So they kill predators in the mistaken belief that it is the best way to be sure that there are plenty of elk, deer, moose, and other targets for the hunters.
This is an odd way to manage wildlife because it goes against a half-century of modern science. In fact, the recognition that predators are the essential managers of ecosystems dates back at least to Aldo Leopold, former wolf killer. In his 1945 essay “Thinking Like a Mountain,” he described mountains overrun by deer, in the absence of wolves, where he had “seen every edible bush and seedling browsed … seen every edible tree defoliated to the height of a saddlehorn” until in the end the deer themselves died from overpopulation and lack of food.
Scientific studies since then have repeatedly borne out this key insight that predators are essential to healthy ecosystems. The University of Washington’s Robert Paine first demonstrated a “trophic cascade”—that is, a cascade of effects through an entire food chain–by removing predatory starfish from a coastal habitat for a classic 1966 study. Mussels, which had previously clung to rocks high up along the tide line, advanced deep into the newly predator-free territory. A mussel monoculture soon displaced limpets, goose-necked barnacles, sea anemones, and other species, destroying the former diversity of life.
Likewise, when researchers asked why kelp forests had disappeared from the coastal waters of Alaska, the answer turned out to be overhunting of sea otters. In the absence of these predators, sea urchins proliferated and nibbled the forest down to the sea bottom. According to a follow-up study early this year, that trophic cascade may explain why the Steller’s sea cow, which grazed on kelp beds, went extinct soon after the beginning of the Pacific maritime fur trade in the eighteenth century.
Since the pioneering research on starfish and sea otters, studies have proliferated demonstrating just how destructive it can be to eradicate predators. You can see a good summary of them here.
Our emotions may tell us that predators are cruel and destructive. Certain badly misguided philosophers have even tried to turn that into an argument for extirpating all predators. But the reality is that this would disrupt ecosystems, set off a chain of extinctions and extirpations, and inflict far greater cruelty on the species inhabiting those ecosystems.
We need to learn to tolerate and even celebrate predators—even predators living in the middle of human communities. Our present mindless program of pushing them to extinction is a prescription for planetary ruin.