Chytridiomycosis, a rapidly spreading disease caused

by a chytrid fungus, had been recorded in 43 countries

and in 36 U.S. states. Responsible for the disappearance

of more than 100 amphibian species worldwide, and

afflicting almost 300 species, this disease is thought to

exacerbate the harm caused by other threats.

Rescue efforts around the globe include testing and

treating animals affected by chytrids (see inset photo).

Large-scale conservation programs, which include

the captive breeding of vulnerable amphibian

species, resulted in the establishment of

the Amphibian Ark, an international

group affiliated with the IUCN

that seeks to preserve

at least 500 species

for reintroduction.

15

Biodiversity and Conservation

DISAPPEARING FROGS

S

ince the 1970s, many of the world’s frog populations

have dwindled or disappeared. At least 42 percent

of the more than 6000 known amphibian species are

declining, and about one-third are threatened or already

extinct. Approximately165 species are believed to be

extinct. Amphibian declines are occurring worldwide,

even in remote, pristine locations, such as the high

reaches of California’s Sierra Nevada Mountains (see

large photograph).

Biologists cannot pinpoint a single cause of the

massive die-offs and suspect they reflect a combination

of threats. According to data accumulated by the

International Union for Conservation of Nature (IUCN),

habitat loss likely causes the greatest harm to these

species, but chemical pollutants, infectious diseases,

increased levels of UV-B radiation, and climate change

are among other factors threatening amphibian

populations (see graph).

graphingactivity