In an e-mail to National Geographic News, lead researcher Fabrizio Sergio explained that the aim of the study was not to justify predator conservation but to test its ecological value.

"Much money and effort are devoted to the conservation of predators, under the assumption that this also benefits other species," he said. "However, such an assumption has never been explicitly and properly tested."

Some conservationists are not surprised by the results of the study.

"The findings are interesting and bring to light relationships that have been suspected but never confirmed," said Berger, the WCS scientist.

"It is nice to see in-depth studies that tout the value of top predators in terrestrial ecosystems, especially birds," he added. "Prior work has concentrated on these sorts of relationships in both marine systems and with large carnivorous mammals."

Manmade Lake

Berger has been studying predator-prey relationships in Montana and Wyoming's Yellowstone National Park and Wyoming's Grand Teton National Park. In both parks top predators like grizzly bears and wolves were eradicated by hunters before the 1900s, leaving bison, moose, and elk to feed and reproduce unchecked by natural predators.

"Where grizzly bears and wolves have been lost, avian biodiversity is less, including fewer warblers and flycatchers," Berger said. "Without grizzly bears and wolves, moose populations built up … and overbrowsed the willow vegetation," which supports the birds.

The recent return of grizzly bears to Grand Teton and the Jackson Hole region, south of Yellowstone National Park, and the reintroduction of wolves into Yellowstone National Park could bring the area back to equilibrium, Berger said.

Removing predators from the ecosystem has also had a cascading effect on animal and plant populations in Lake Guri, Venezuela. The lake was created after the construction of a hydroelectric dam on the Caroní River there.

As the region was swamped by the new lake and hilltops turned into small islands, top predators like jaguars and harpy eagles fled the area.

In the predators' absence, their prey—howler monkeys, iguanas, leaf-cutting ants—multiplied on the newly formed islands. Soon these plant-eaters had devoured most of the once pristine forest.

"The impact of massive herbivory [plant eating] was to increase the mortality of trees and especially saplings and to reduce recruitment of new individuals into the population," said John Terborgh, a professor of environmental science at Duke University in Durham, North Carolina.

A Bad Name

Part of the criticism against using top predators as poster animals is that these animals are often highly unpopular with the people who have to live with them.

"Lavishing money on protecting species that eat people's livestock and threaten their families can create antagonism between conservationists and local communities," said Bob Smith of the Durrell Institute of Conservation and Ecology at the University of Kent in England.

"That's why there have been moves towards a more balanced approach, which encourages people to live alongside these species by giving them benefits through ecotourism or trophy hunting," he said.

In the past large carnivores have often been used as "umbrella" species, with the assumption that conserving them will conserve enough habitat for a range of other species.

"Choosing areas based only on these large predators is definitely a flawed approach, as things like leopards and tigers are often habitat generalists," Smith said. "It's perfectly possible to conserve them in biodiversity-poor habitats while failing to conserve things with a restricted range."

For his part, lead researcher Sergio said that more study is still needed before the impacts of predator conservation can be fully understood.

"About future studies, one word of caution," he said. "Our study was made in the Alps, and it does not automatically mean that top predators will be biodiversity indicators everywhere. The same sort of study should be made in other ecosystems to test whether this is a world-wide phenomenon or only a local one."

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SOURCES AND RELATED WEB SITES Nature Wildlife Conservation Society Center for Tropical Conservation (Duke University) Durrell Institute of Conservation and Ecology