The Crucial Role of Predators: A New Perspective on Ecology

Image Gallery  The return of wolves to Yellowstone proved that damage to a terrestrial food web could be restored. FOTOLIA

Found in the North Palace at Ninevah, stone panels depicting the Royal Lion Hunt of the last Assyrian king, Ashurbanipal, are as violent as any video game: A female lion flies upside down, arrows protruding from her back and belly. Beneath her, a male rears back, arrows piercing his nasal passages while another male drags his hindquarters behind him. From the king’s chariot, attendants drive spears through the chest of another.

The panels are two-and-a-half thousand years old, and the story they tell is nearly over. In Africa, the lion’s numbers have declined sharply in the past decade, to as low as 23,000. The tiger is near extinction. Earlier this year, a mountain lion walked 1,800 miles from the Black Hills of South Dakota to the East Coast — one of the world’s longest recorded journey by a land mammal — only to be killed by a sport utility vehicle near Milford, Connecticut, 50 miles from New York City.

Just as the world’s lions, tigers, and bears are disappearing worldwide, a scientific consensus is emerging that they are critical to ecosystem function, exerting control over smaller predators, prey, and the plant world. Studies  of predation — a so-called “top-down” force in nature — have always run a weak second to ecology’s traditional focus, which holds that the foundation of life springs from bottom-up processes enabled by plants capturing energy from the sun. While no one disputes the importance of photosynthesis and nutrient cycling, experts on predation have become increasingly convinced that ecosystems are ruled from the top.Beginning with aquatic experiments, they have amassed considerable evidence of damage done to food chains by predator removal and have extended such studies to land: Predation may be as consequential, if not more so, than bottom-up forces. With a comprehensive new book (Trophic Cascades) and a major Science review published this summer, these specialists present the case that our persecution of predators menaces the marine and terrestrial ecosystems that produce food, hold human and zoonotic diseases in abeyance, and stabilize climate.

Using such terms as “deep anxiety” and “grave concern” to signal their alarm, the authors contend that the loss of large animals, and apex predators in particular, constitutes humanity’s “most pervasive influence” on the environment. It amounts, they argue, to a “global decapitation” of the systems that support life on Earth.