Warning on loss of world's top predators

The dramatic decline of the world's top predators, from wolves and lions to sharks and tuna fish, represents one of the most destructive human influences on the natural world, a group of leading biologists has found.

Top predators are the "apex consumers" of the world's ecosystems and their decline in numbers has powerful repercussions on animals and plants lower down the food chain, says in a study published in the journal Science. The decline, from such activities as hunting and habitat loss, has had diverse effects, from changes in vegetation and wildfire frequency to water quality and nutrient cycles, the scientists said.

"Apex consumers... have powerful effects on the ways ecosystems work, and the loss of these large animals has widespread implications," said Professor James Estes of the University of California, Santa Cruz.

The loss of wolves from Yellowstone National Park, for instance, led to serious woodland overgrazing by elk.