Program is part of a world-wide effort to prevent the single largest mass extinction since the disappearance of the dinosaurs
Jun 05, 2008 04:30 AM
Peter Gorrie
STAFF REPORTER
Deep in the bowels of the Toronto Zoo's service building, offlimits to the public, the reptile room is uncomfortably warm and humid.
Most of the snakes and lizards snoozing in white plastic bins prefer it toasty warm. A few, though, lurk in tanks where chillers work overtime to keep a few centimetres of water at a brisk 18 to 20C. Among them are Panamanian golden frogs and lemur leaf frogs, and their need to keep cool is part of the reason they could soon vanish from the face of the Earth.
Toronto's zoo is one of 20 around the world trying to stop that from happening to these and dozens of other frog species able to live only where the climate is on the frosty side. Visitors can learn about the effort this summer as the zoo marks the international “Year of the Frog.”
Amphibians face a wide array of threats: Climate change, pollution, ozone depletion and destruction of habitat are taking a devastating toll. As a result, the zoo says, Earth faces the single largest mass extinction since the disappearance of dinosaurs.
About 120 of the world's 6,000 frog and toad varieties have vanished and up to half could be wiped out in our lifetime. But the threat facing the cool-climate species is so imminent and potent that the zoos have launched a last-ditch rescue attempt. It's a fungus called Batrachochytrium dendrobatidis. It causes a disease known as chytridiomycosis, which prevents frogs and toads from absorbing moisture and oxygen through their skin — the only way they can take them in. There's no defence against it, and no cure in the wild. The only thing that stops the fungus in its tracks is a warm temperature: It doesn't survive above 34C.
At risk are frogs and toads that live in cool, moist “cloud forests” high in the mountains of tropical and temperate countries. Surrounded by impassable warm lowlands, these isolated, elevated enclaves offer no escape when harm comes calling.
Bob Johnson has seen chytrid's impact first-hand. Back in 1987, this world-renowned frogophile, who has been at the zoo for 35 years and is now its curator of reptiles and amphibians, was in Costa Rica to study golden toads. They were abundant in the Central American country. The fungus roared through and, within two years, the golden toad had vanished from Earth forever.
“I've experienced extinction,” Johnson says. “I was one of the last people to see them.”
He doesn't want it to happen again. Frogs and toads are a vital part of the food chain, he says.
“They're so big a part of the ecosystem — a building block of what keeps it together.”
On top of that, they're endlessly fascinating creatures that he loves to watch and encourage. Amphibians have evolved an astonishing array of features that enable them to survive daunting conditions. One example: They need a continuous supply of moisture. Drink pads on their rumps let them extract molecules of water while they sit on seemingly dry soil. But they are very sensitive to alterations in the niches they inhabit, and change is happening almost as fast as they can snag insect meals with their tongues.
The zoo exhibits frogs and toads in several pavilions: The effort to ward off chytrid is explained in the Americas area. The fungus has likely existed for eons but, like many other sources of disease, was contained in a few small areas until humans liberated it. It now lurks in virtually every suitable habitat, and, so far, can't be eliminated.
Attempts to reintroduce frogs and toads to affected areas are futile. The fungus, which interferes with the absorption of moisture and oxygen through their skin, would quickly find them. Enter the zoos. They've collected specimens of as many threatened species of frogs and toads as they can. The aim is to create a sort of Noah's Ark — to keep the frogs safe and sound so that if the fungus is ever eradicated, they can be released back in their original homes.
“If someone had taken golden toads in 1987, we'd still have that beautiful amphibian,” Johnson says.
About 400 of each species are required to ensure a wide and deep gene pool, so each zoo keeps a few, and they're exchanged for breeding. With careful breeding, the zoo populations can be kept genetically healthy for about 100 years, Johnson says. That's not as long as it seems, he adds. No cure is in sight.
