Between 1987 and 1988, the hottest year on record until then, two small inhabitants, the golden toad and the Monteverde harlequin frog, disappeared from the Monteverde Cloud Forest Preserve in Costa Rica. That same year, the jambato toad vanished from the highlands of Ecuador, which was also unusually hot and dry.
The frogs' disappearance is part of an ongoing worldwide amphibian die-off. Of the 5,918 known amphibian species, an estimated 165 may have already disappeared, according to the World Conservation Union (IUCN). Nearly one-third of those remaining face extinction. Many are calling it the canary in the coal mine, a sign of things to come. As the world warms from human-emitted greenhouse gases this century, one-quarter of all living things could disappear, says the Intergovernmental Panel on Climate Change.
Little is known about what would happen if amphibians, a large and ancient class of animals, disappear.
In some Appalachian forests in the United States, the total mass of the amphibians – frogs, toads, newts, and salamanders – outweighs that of all the mammals, birds, and reptiles combined. Amphibians hold a crucial middle position in the food chain. They eat bugs, plants, and algae. Many other animals eat them. Because they live on both land and in the water, they transfer large quantities of organic matter between the two. "You can't simply lose large numbers of species ... and expect these ecosystems to continue to function," says Alan Pounds, an ecologist working at Monteverde.
Michael Fogden, an ornithologist-turned-photographer who's lived for 30 years at Monteverde, has observed many changes, some related to fewer frogs, all related to changing weather.
Resplendent quetzals, iridescent tropical birds that he used to observe feeding frogs to their young, are scarcer. Quetzal hatchlings may have lost a vital source of protein and calcium with the disappearance of once-abundant amphibians, he reasons. Keel-billed toucans, meanwhile, have moved up from the foothills to the mountain, perhaps competing with the quetzal. So has the morpho, a bright blue lowland butterfly. Snakes, which also fed on the frogs, are much harder to come by even as lowland honeybees that previously avoided the mountain's hive-infesting fungi now swarm up the mountain.
"We lived in cloud forest when we first arrived," Mr. Fogden says. "It's not cloud forest anymore, really."
Besides losing potential ingredients for new drugs or other useful compounds, scientists worry about more lost benefits as species vanish. Healthy ecosystems are complex. Complexity lends resilience, the ability to ride out disturbances. A resilient ecosystem will continue delivering the "services" humans expect, whether it's harvesting abundant tuna from the sea or tapping fresh water as it tumbles down a mountainside. Each species removed from an ecosystem brings it closer to a largely invisible threshold of collapse.
Scientists tend to use this economic reasoning about nature's importance when talking with journalists. When pressed, though, they make a different argument.
Species "should be preserved because of their intrinsic value," says Kayri Havens, director of the Institute for Plant Biology and Conservation at the Chicago Botanic Garden, "because they deserve to exist. Just as we do."