In ecosystems around the world, the decline of large predators such as lions, wolves, otters and bears is changing the face of landscapes.
Ironically, they are vanishing just as the scientists are learning about their important ecological effects.
A significant analysis of 31 carnivore species shows for the first time how threats such as habitat loss, persecution by humans and loss of prey combine to create global hotspots of carnivore decline.
More than 75 percent of the 31 large-carnivore species are declining, and 17 species now occupy less than half of their former ranges, the authors reported in a study published in the journal Science.
Southeast Asia, southern and East Africa and the Amazon are among areas in which multiple large carnivore species are declining.
"With some exceptions, large carnivores have already been exterminated from much of the developed world, including Western Europe and the eastern United States," said William Ripple, lead author and a professor in the Department of Forest Ecosystems and Society at Oregon State University.
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The researchers reviewed published scientific reports and singled out seven species that have been studied for their widespread ecological effects.
This included African lions, leopards, Eurasian lynx, cougars, sea otters and dingoes.
"Many of them are endangered. Their ranges are collapsing. Many of these animals are at risk of extinction, either locally or globally," Ripple added.
Human tolerance of these species is a major issue for conservation. These animals have an intrinsic right to exist, but they are also providing economic and ecological services that people value, the study noted.