Amphibians at Greatest Risk Have Common Traits

The largest analysis ever undertaken of what makes the existence of amphibians most precarious finds a single characteristic predominates.

Species confined to a small geographic area are those most likely to have declining populations and be threatened with extinction.

Frogs, toads and salamanders with tiny ranges are not uncommon and on the whole amphibians have not been doing well lately.

Censuses recorded for over 4000 amphibian species from 1980 to 2004 show that 61 percent of species declined in number, while less than 1 percent increased, with the rest remaining stable.

Extinction now threatens nearly one-third of the world's amphibians that have been studied. Plus, over a fifth of amphibian species are still not well enough known to determine whether they are endangered.

Besides range area, several other factors also tend to tip the scales towards a species' demise. The main one is body size: larger creatures are more likely to be imperilled. Being a big frog in a small area makes a lousy combination for species survival.

Continued existence seems further frustrated by variable climate. Animals living where temperature and precipitation swing markedly from season to season are among those at higher risk of extinction. Habitat losses and high densities of people in the area can additionally predispose a species to being endangered.

Species in decline also tend towards certain life history traits. Living in water or in trees and certain reproduction strategies correlate with diminishing populations.