By Matt McGrath Environment correspondent, BBC News
Three quarters of the world's big carnivores - including lions, wolves and bears - are in decline, says a new study.
A majority now occupy less than half their former ranges according to data published in the journal, Science.
The loss of this habitat and prey and persecution by humans has created global hotspots of decline.
The researchers say the loss of these species could be extremely damaging for ecosystems the world over.
The authors say that in the developed world, most carnivorous animals have already succumbed to extinction.
When they looked at 31 big meat eaters, they found that they were under increasing pressure in the Amazon, South East Asia, southern and East Africa.
"Globally, we are losing our large carnivores," said lead author Prof William Ripple from Oregon State University.
"Their ranges are collapsing. Many of these animals are at risk of extinction, either locally or globally."
Prof William Ripple Oregon State University
Human tolerance of these species is a major issue for conservation”
The researchers say their work highlights the important ecological role of many of these carnivores.
When they looked at wolves and cougars in Yellowstone National Park in the US, they found that having fewer of these big predators resulted in an increase in animals that browse such as elk and deer.
While this might seem like good news, the researchers found that the rise of these browsers is bad for vegetation and disrupts the lives of birds and small mammals, leading to a cascade of damaging impacts.
Similar effects were seen all over the world.
The rise of olive baboons in Africa has been linked to the decline of lions and leopards. But the baboons now pose a bigger threat to farm crops and livestock than elephants.Paying the price
The scientists say that much of the problem comes from an old fashioned notion that predators are harmful and just a threat to other wildlife.
The authors say there needs to be a rapid recognition of the complex roles these carnivores play and how much they are worth in economic terms.
And when people try to replicate the services provided by these animals, they aren't as effective.
"Human tolerance of these species is a major issue for conservation," Prof Ripple said.
"We say these animals have an intrinsic right to exist, but they are also providing economic and ecological services that people value."
Among the services of value that have been documented in other studies are carbon sequestration, biodiversity and disease control.
When large carnivores are re-introduced, such as with wolves in Yellowstone, the ecosystems tend to respond rapidly.
"I am impressed with how resilient the Yellowstone ecosystem is. It isn't happening quickly everywhere, but in some places, ecosystem restoration has started," Prof Ripple explained.
The authors argue that there needs to be an international
initiative to conserve these larger carnivorous species in a peaceful
co-existence with humans.