One way to help species facing habitat loss: 'escape routes'

As the world warms from human-emitted greenhouse gases during this century, one-quarter of all living things could disappear, says the Intergovernmental Panel on Climate Change.

Robust, genetically diverse populations have a much better chance of weathering this climate change than those that are inbred and few in number, scientists say. So the best way to help wildlife persist through this trying time is to give it ample room to feed, breed, and multiply.

This means preserving tracts of wilderness large enough to establish healthy populations. And it means establishing "biological corridors" between wilderness areas – especially up mountainsides and through north-south pathways – so wildlife can move as climate changes.

Groups around the world are working to establish these wildlife highways, with varying degrees of success. In North America, the Wildlands Project is pushing for a huge "Yellowstone-to-Yukon" wildlife corridor. In Central America, conservationists are slowly and sporadically working on the Meso-American Biological Corridor. The dream: A monkey should be able to go up a tree in Panama and not have to climb down until it reaches Mexico. The grand vision of the IUCN is an uninterrupted connection between Argentina and Alaska along the hemisphere's western mountain ranges.

But the golden toad's disappearance has weakened one of the assumptions underlying these efforts: Setting aside a reserve doesn't necessarily shield species from extinction. Wildlife is vulnerable even in protected areas.

"It's not enough," says Alan Pounds, scientist-in-residence at Costa Rica's Cloud Forest Preserve. "You have to consider the entire landscape." Indeed, scientists recently found that pesticides sprayed over lowland banana and pineapple plantations in Costa Rica waft up to the highlands. In some areas, they reached concentrations 10 times higher than right next to the plantation. Studies show that frogs living downwind from pesticide plumes have a greater chance of disappearing than those that don't.

And for highly specialized animals, like those trapped atop tropical mountains, corridors will help little. In these cases, some scientists call for an "amphibian ark," a network of zoos that breed amphibians in captivity with the goal of one day reestablishing wild populations.

At El Valle Amphibian Conservation Center (EVAC) in Panama, researchers recently succeeded in breeding the golden frog (not to be confused with the extinct golden toad), a species native to the area – and none too soon. Last year, the frog disappeared from the wild. "Chytrid came and basically gave the last blow," says EVAC director Edgardo Griffith.

Recent findings have raised some hopes of developing a chytrid vaccine, which could combat one cause of extinction. But scientists can't inoculate all of nature. Even if it were possible, the prospect quickly becomes prohibitively expensive when contemplating the mass extinctions predicted for the 21st century.

That's why some advocate "assisted migration," moving plants and animals before the climate changes too much.

This approach solves problems foreseen if natural selection runs its course in an unnatural setting. "If the only species that can migrate through disturbed habitat are weedy species, then those are the species you're going to get," says Jason McLachlan, assistant professor of biology at the University of Notre Dame in Indiana. These are the cockroaches, ragweeds, and jellyfish of the world, species that humankind generally finds neither useful nor aesthetically pleasing.

But moving species raises a host of sticky questions. What should an ecosystem that has never existed before in a particular place look like? What happens if the assisted species threaten the existing wildlife in their new location?

Despite many concerns, Professor McLachlan increasingly sees assisted migration as inevitable. "If elephants start going extinct because of climate change, people are going to move them," he says. "So the question is, 'What would be the effects of moving elephants to a new area? And how physically would you do it?' "

Any successful efforts to soften global warming's impact on wildlife will likely include a combination of tactics. But scientists see them as equivalent to an escape hatch or a backup parachute – a last-ditch effort. Except for corridors and reserves, these measure are not sustainable or cost-effective in the long term, they say.

The real solution is the most obvious, Pounds says: stop and eventually reverse greenhouse-gas buildup from human activity. And this fix ultimately depends on people. "If constituencies demand change, then you'll see that happen," he says.