These precipitous declines are widespread across a large area of rain forest, suggesting that habitat destruction by itself is not a likely cause. In Yosemite National Park in the United States, scientists recently discovered the large-scale collapse of an entire community of amphibians. Surveys conducted in 1992 revealed that all seven native species of frogs and toads in the region of Yosemite have declined since 1915. Three species have disappeared entirely from this nearly pristine National Park. The only species that was reported to be more widespread is the one non-native species, the bullfrog, which was introduced to the area in the late 1800s.
Amphibians are now the object of intensive studies to solve the mystery of their decline.
Where habitat destruction is not the obvious cause, it is thought that other, less-visible problems, such as pollution, acid rain, drought, disease, human exploitation, and ozone depletion may be killing the animals. Overexploitation Amphibians are part of the diet of many local peoples around the world. A low level of subsistence hunting rarely decimates a population. The recent rise in commercial utilization of frogs, however, has been deleterious. Demand is also growing in the United States.