The global amphibian crisis.(YEAR OF THE FROG)

A crisis of enormous proportions faces the world's amphibian species. At present, we estimate that about one-third of the more than 6,000 known amphibian species are at risk of extinction. This likely underestimates the real number since data are lacking on many species from Africa, Southeast Asia, and other regions. Several causes underlie this massive decline, but a crucial element is the very nature of amphibians; their skin must always be moist and it literally breathes, so they are especially vulnerable to environmental contaminants. Habitat destruction, disease, pollution, climate change, and other expanding human-related impacts have an entire class of the animal kingdom in serious decline.

Frogs hold great cultural significance. They figured prominently in ancient Egyptian and Greek mythology, as well as more recent folklore. Today's well-known character Kermit the Frog, whose motto is "It isn't easy being green," may have had an early premonition of the crisis frogs face today. Frogs were traditionally used for studying anatomy, physiology, neurobiology, and pharmacology, and were used globally in the 20th century for pregnancy tests. Today, as we see amphibian species in serious decline, frogs are like the "canary in the coal mine"--a class of animals more sensitive than most, potentially signaling an impending environmental calamity.

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The severe decline of amphibians occurring today can be compared with the mass extinction of dinosaurs 65 million years ago. Yet, while most people know of the sudden disappearance of dinosaurs, few remember that when the dinosaurs disappeared, almost 70 percent of the other species on Earth disappeared with them. There could be truth in the notion of amphibians as an early indicator of environmental chaos. However, unlike the demise of dinosaurs, many of the impacts that threaten amphibians are of human origin.

The most serious threat to amphibians is habitat loss and widespread habitat fragmentation. Loss of rainforest and other crucial habitats to agricultural and other human development is devastating habitats crucial to amphibian survival worldwide. Pollution from mine drainage, pesticides, fertilizers, and other organic compounds is present in every earthly ecosystem. Amphibians are particularly susceptible to the effects of organic molecules since their skin is so much more permeable than that of other animals. A disease caused by the pathogenic fungus Batrachochytrium dendrobatidis is spreading undaunted, with few amphibian species showing resistance. The chytrid disease typically results in mass die-offs where often more than 50 percent of amphibian species are extirpated within six months, while other species persist with relatively minor reductions. Meanwhile, amphibians are also affected by harvesting for food and the pet trade, predation, and invasive introduced species.

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