Amphibians are animals that can live both on land and in water. A new global assessment has found that 41% of amphibian species that scientists have studied are threatened with extinction. That's up from 39% reported in the last assessment in 2004.
The study, published on Wednesday in the journal Nature, found that the loss of habitat from the legal and illegal expansion of farming and ranching （放牧） contributes most to the extinction risk of amphibians worldwide. But a growing percentage of amphibian species are now also pushed to the edge of extinction by novel diseases and climate change, the study found.
Amphibians have distinct life stages that each often require separate habitats, so they can be disturbed by changes in either water or land environments, said University of Texas biologist Michael Ryan, who was not involved in the study. They are also at risk because of their delicate skin. Most amphibians absorb oxygen to breathe through their skin, and so they do not have scales （鳞）, feathers or fur to protect them. Chemical pollution，bacteria and fungal（真菌的） infections impact them quickly, as do heightened swings in temperature and dampness levels due to climate change.
For example, frogs are active usually at night. If it's too hot, they won't come out even at night because they would lose too much water through their skin, said co-author and researcher Patricia Burrowes. But remaining in sheltered resting places limits frogs' ability to eat and to produce.
Juan Manuel Guayasamin, a frog biologist at the University San Francisco of Quito,Ecuador, said that advances in technology to track animals and climate variations allowed the new study to use much more precise data than the 2004 assessment."We have a much better understanding of some risks," said Guayasamin.
The study identified the greatest concentrations of threatened amphibian species in several biodiversity hot spots, including the Caribbean islands, the tropical Andes, Madagascar and Sri Lanka. Other locations with large numbers of threatened amphibians include Brazil's Atlantic Forest, southern China and the southeastern United States.
