Rainforest frogs: vanishing act? Frog populations around the world are dying off mysteriously. Can scientists save them—before it's too late?

Science World, March 11, 2002 by Kim Y. Masibay

RAINFORESTS SEEM to have everything any frog could crave--lots of water, an endless variety of bugs to prey oil, and thousands of hiding places. No wonder more than 2,100 frog species call rainforests their home. In a 3-square-kilometer (1.16-square-mile) site in Ecuador, "we found 81 different frog species," says William Duellman, leading tropical frog expert. "That's almost as many species as we have in all of North American!"

Biodiversity has long lured tropical field biologists (life scientists) like Duellman to rainforest. And while these explorers continue to stumble on never-before-seen frog species in fertile jungles, they're also startled to discover that hundreds of frog species are abruptly declining--and even extinct. "It used to be that in the Andes of Ecuador, toads were so abundant you had to be careful not to step on then," recalls Duellman, who is also curator emeritus of herpetology (reptile and amphibian science) at the University of Kansas Natural History Museum. "Now, they're gone." And not just in South American rainforests.

Amphibians like frogs, toads, and salamanders are dying off worldwide--especially in pristine cloud forests, rainforests so high in mountains that trees draw moisture directly from clouds. "We study frogs in national parks--the most protected areas," explains Karen Lips, a Southern Illinois University herpetologist. "There, no one's logging or spraying pesticides. But frogs are still dying. Why?"

There are multiple theories:

* Habitat destruction. "Dart-poison flogs deposit tadpoles in water-holding plants," says Jack Cover, general curator of fishes and rainforest exhibits at the National Aquarium in Baltimore, Maryland. "Clearcut the forest and the flogs lose the tools they need to reproduce."

* Pollution and climate change. A frog's skin is porous, riddled with tiny holes that easily absorb pollutants in air and water. For that reason they're called indicator species: Their health may mirror the well-being of the planet. Strong evidence suggests Earth's climate is warming, and at the Monteverde Cloud Forest Preserve in Costa Rica, biologist Alan Pounds has witnessed 20 of 40 frog species disappear from a 30-square-km (11.58-sq-mi) study area since 1989. Weather data suggests that global warming has caused clouds to shift upward, decreasing the amount of mist in the cloud forest--which impacts frogs' ability to thrive.

As ectotherms, frogs' body temperatures depend on surrounding temperatures. And many rainforest frogs are specialized to survive in specific habitat niches (places). Even slight changes in temperature or moisture disrupt their life cycle.

* Disease. Some biologists believe that a global disease-causing fungus (plant with no leaves, flowers, or roots) may rival habitat destruction as the largest single cause of amphibian population declines.

Frogs have existed on Earth for nearly 200 million years. "That's a pretty impressive amount of time to be around," says Coven "We can only hope they hang on through whatever this is."

MASS MURDER

Frogs are food to so many snakes and birds, a herpetologist could spend many seasons in some places without seeing a dead frog lying on the ground. So imagine Karen Lips's shock when she returned to her research site in western Panama and discovered dead and dying frogs everywhere: "I'd been going to Fortuna, Panama, since 1993. In 1997, I returned to find all these dead frogs. They looked fine, like they went to sleep and didn't wake up."

Lips collected bodies for autopsy. Cause of death? A fungal organism called chytrid had pervaded the frogs' skin--essentially the fungus suffocated them. Now researchers have found a plague of chytrid in moist, high-elevation forests throughout North, Central, and South America, as well as Australia.

Chytrid and frogs might have always shared a habitat. "But now something is off-balance, causing a disastrous interaction between flogs and fungus," Lips says. "Something's different." But what? That's where experiments come in, she explains. She's now comparing aspects of Fortuna with her new research site, El Cope in central Panama. Species that disappeared from Fortuna can still be found at El Cope, including four or five species of glass tree frogs.

Fearing another die-off like that at Fortuna, Lips wracks her brain to form strategies to save frogs. One option: an emergency captive-breeding program, "as a last-ditch measure only," she says. The idea is to preserve each species in captivity to prevent extinction, should something catastrophic happen to the wild populations. "We can put them back into the wild when"--or if--"the environment is okay again."

The National Aquarium has successfully bred 27 species of dart-poison frogs since 1996. Complex chemical toxins called alkaloids in these frogs' brilliantly colored skin excite medical researchers, who see the alkaloids as possible sources of potent new medicines to treat human diseases. "But there's a problem," says Jack Cover. "The ones we raise in captivity don't produce alkaloids at all."