Predators such as wolves, bears and panthers are being reintroduced close to where people live, as a growing number of scientists believe they may hold the key to restoring damaged ecosystems.

"It used to be we would see it once every year or so, but now it's every two weeks," said Al Sanchez.

"I'm starting to panic when I hear noises. If I come out here I'm concerned I'm going to be his prey."

Mr Sanchez and Reg Malone, who live in a densely populated suburbs of Naples, Florida - a city of 300 000 people - are regularly visited by a Florida panther, a sub-species of the cougar, and have been left unnerved by the close encounters.

It's different to going to a park and seeing it in the park... we're in the park! Al Sanchez, Florida resident

As the Florida panthers' habitat dwindled and they were hunted, their population dropped to 30 by the early 1990s.

With the threat of extinction looming, a team at Florida's Fish and Wildlife Institute reintroduced the predators to the area around Naples. They also hoped they might attack a wild hog population that was out of control.

Now there are more than 100 of the animals, but they have to co-exist with people.

Institute team member Mark Lotz told Mr Sanchez and Mr Malone: "I don't think you're in a lot of danger there, because people aren't on their menu to eat.

"But when they're on a kill that's probably when they're most dangerous because they're going to want to defend that kill.

Reintroduced predators Florida panthers, Florida, US

Gray Wolves, Wyoming, US

Brown bears, The Alps, Italy

"The best thing is don't take your eyes off it, walk backwards.

"But if he is approaching you, (see) if there's something nearby to pick up and throw at him. You can also hold your arms up and make yourself look bigger than him."

Dominant species

Humans have not always been the dominant species on earth.

For millions of years before our arrival, predators like wolves, bears and big cats were the creatures at the top of the food chain that nothing could touch.

Find out more Horizon: Predators in Your Backyard will be on BBC Two at 2100 GMT on Tuesday 8 March Catch up on BBC iPlayer

Over the years humans have trapped, caged and killed predators, and now ecosystems across the world are notable by the absence of these animals. The wild is no longer truly wild.

A growing number of scientists think that this has been a mistake.

They see predators not as dispensable, ruthless killers, but an essential component of healthy ecosystems - which is why they want to put them back in to the wild.

But the modern world is not predator-friendly. Urbanisation and road building, which can fence animals in, have made it difficult for predators to avoid genetic problems due to inbreeding.

Image caption Wolves, bears and big cats used to be at the top of the food chain

Mr Sanchez said he accepted the big cats would be staying in his neighbourhood.

"It's just learning to live with it and the close encounters.

"It's different to going to a park and seeing it in the park. We're in the park!" he said.

But for the panthers to survive independently of the scientists and escape the problem of inbreeding, the Naples project needs to expand so there are more core populations across central and northern Florida they could mate with.

Without the exchange of genes between two or more core populations, the panther population will never fully recover.

One way to do this, is by providing the predators with "wilderness corridors" so that they can roam and breed across southern states such as Alabama, Georgia and as far north as Arkansas.

But it is an idea that remains on the drawing board because of the opposition it has aroused.

Returning wolves

The full impact of returning predators to the environment can be seen at Yellowstone National Park in Wyoming, where the wolf was reintroduced the mid-90s after being exterminated there 70 years before.

For the past 15 years, the leader of the Gray Wolf Restoration Project Dr Doug Smith and his team have monitored the effects of wolves on Yellowstone.

Thirty-one of the animals were released in 1995 and 1996, and Dr Smith now puts the number at about 100.

Their research suggested that predators not only influence the numbers of plant-eating animals through predation but through a complex series of interactions in the ecosystem, the predators can also restore forests.

We know they occasionally kill us - we're going to have to work through that, but it's worthwhile Dr Doug Smith, The Gray Wolf Restoration Project

Dr Smith has noticed dramatic changes amongst the willow stands that grow in Yellowstone's river valleys.

He said: "When I first came to Yellowstone about 16 years ago the willows here were all eaten by elk.

"But since wolves have been reintroduced we saw the willow come back, before our eyes. A big factor is, very simply, wolves eat elk, so it's connected."

The absence of wolves between 1926 and 1995 coincided with a loss of beaver populations in the park, but since the wolves returned, beavers have been drawn back by the increase in willow.

Now that the beavers are back and building dams, the water table in areas of the park that were suffering from deforestation has begun to rise, restoring populations of water hungry species of tree like willow and aspen.

"The missing piece of the puzzle was the wolf, the top predator," Dr Smith said.

"We lost them in the early part of the last century, we gained them late in the century and 10 to 15 years out we've moved back closer ecologically to where we were about 100 years ago. This is really exciting stuff."

The return of the predator to our world is not without risk and difficulty, but Dr Smith sees predators as a crucial ally in the ongoing battle to reverse environmental decline.

"We know they compete with us. We know they occasionally kill us.

"You know we're going to have to work through that but it's worthwhile.

"If we're going to restore wild nature, if we're going to preserve it, these top predators have a key part in that."

For scientists like Dr Smith, the potential rewards of bringing back predators outweigh the logistical complexities and risks of their return. They believe we have to stop hating predators and learn to live with them, for our own good.

Horizon: Predators in Your Backyard will be on BBC Two at 2100 GMT on Tuesday 8 March and after on BBC iPlayer.