I first discovered this story through a MetaFilter thread from 7 June 2004, featuring a Scientific American article, “Lessons of the Wolf.” So imagine my surprise to see the story resurrected by Ran Prieur. It seems that Dr. Douglas W. Smith has a new book coming out on the subject, Decade of the Wolf : Returning the Wild to Yellowstone, which led to his lecture last Tuesday at the American Museum of Natural History in New York City–which led to a piece in The New York Times by the same Jim Robbins who wrote the original piece for Scientific American last year. Ahh, symmetry. At any rate, since I first read it, it has become one of my favorite examples of the effect that alpha predators have on an ecology, so this seems like an excellent opportunity to comment on it.

Ran quotes the New York Times piece thus:

…wolf predation has been significant enough to redistribute the elk. … They do not spend time in places where they do not feel secure — near a rise or a bluff, places that could conceal wolves. In those places willow thickets, and cottonwoods have bounced back. Aspen stands are also being rejuvenated. … Where willows and cottonwoods have returned, they stabilize the banks of streams and provide shade, which lowers the water temperature and makes the habitat better for trout, resulting in more and bigger fish. Songbirds like the yellow warbler and Lincoln sparrow have increased where new vegetation stands are thriving. … The number of coyotes, on the other hand, has fallen by half. Numbers of their prey — voles, mice and other rodents — have grown. And that, in turn bolsters the populations of red foxes and the raptors.

In the more recent piece, Dr. Smith is quoted with saying, “Wolves have caused a trophic cascade.”

Humans eliminated the wolves from Yellowstone because wolves prey on domesticated livestock. Their campaign against wolves was bolstered by the many legends and myths of wolves that prevail in European folklore. Another article, this one from National Geographic and published even earlier (4 December 2003), was “Wolves’ Leftovers Are Yellowstone’s Gain, Study Says.” It outlines how wolves were exterminated in Yellowstone:

Wolves were systematically hunted in Yellowstone and much of the Western United States from the 1800s onwards. Yellowstone’s last pack was eliminated in 1926.

“In the early 1900s no one stopped to consider the ecological role of wolves,” commented Robert Beschta, a forestry scientist at Oregon State University in Corvallis. “Wolves were considered a predator with no value and seen as a huge constraint on allowing a productive ecosystem to flourish,” he said. Wolves, mountain lions (Puma concolor), and coyotes (Canis latrans) were all targeted as threats to livestock and game, he said.

What other animal spends its energy actively hunting its competition? This is precisely what led Daniel Quinn to coin the redundant term, “totalitarian agriculture,” to refer to our transgression of his “Law of Life,” which is: “You may compete to the best of your abilities, but you may not wage war.” In an early draft of Ishmael preserved as the underground cult classic, Book of the Damned, Quinn warns that the consequence of being such “an outlaw” is, ultimately, extinction.

Ecologists puzzled over the devastation of Yellowstone that followed. Elk herds boomed, but everything else faded. The trees disappeared, and a cascade spread throughout the park. Without their predators, elk populations skyrocketed. They ate the blossoms of willow trees–and before long, had so stripped their food source that they even ate the young sprouts, keeping willows from ever reaching significant maturation. The entire ecosystem of the park suffered.

Jim Robbins closed the older, Scientific American piece thus:

Wolves have brought other lessons with them. They dramatically illustrate the balance that top-of-the-food-chain predators maintain, underscoring what is missing in much of the country where predators have been eliminated. They are a parable for the unintended and unknown effects of how one action surges through an ecosystem. More important, the Yellowstone wolves are bringing into focus hazy ideas of how ecosystems work in a way that has never been so meticulously documented. Just as the actions of the wolf echo through Yellowstone, they will reverberate into the future as they help to increase the understanding of natural systems.