Threatened species of Amphibians

Due primarily to the impact of man on the natural environment, whether directly or indirectly, many of the 2,000 species of amphibia are in danger of extinction. Populations of frogs, toads and salamanders appear to be declining in many places around the world (including North, Central and South America, Europe, Asia, Africa and Australia), even from wilderness areas apparently unexposed to levels of pollution characteristic elsewhere. Specifically, at least one-third of North America's 86 frog and toad species and ten percent of Australia's 194 frog species are in serious decline. This has been variously attributed to acid rain, to pesticides, viruses and to adverse weather conditions. In 1994, scientists noted that eggs of frog and toad species which do not appear to be declining have high concentrations of an enzyme, photolyase, which protects them against the effects of ultraviolet radiation. The hatching rates of vulnerable frogs' eggs were significantly improved by shielding them from the sun. This suggests that the cause could be damage to the ozone layer.

The Golden toad appears to have become extinct, along with 20 other species of toads and frogs which have disappeared since 1987.

Frogs around the world are being wiped out by what was a mystery disease until scientists at the Australian Animal Health Laboratory identified the killer as the chytrid fungus in 1998. The fungus is selective. In some places the fungus has arrived and every single frog of an entire species has died within a 12 month period. In other places there is no effect at all -- lots of frogs, some of them are even infected and certainly not dying. The fungus is responsible for at least five extinctions in Australia. It is probably the major factor in the decline of at least a couple of dozen other species. Many of our common frogs are now infected with it and are just not as common as they used to be.

The Savannah River Ecology Laboratory (SREL) began research in Rainbow Bay (USA) in 1978. This 20-year study is the longest running project of its kind in the world and is considered to be a model for the type of long-term studies that are required to understand the effects of climatic fluctuations and habitat disturbances on natural amphibian populations. Such long-term intensive studies of a single natural community have revealed that amphibian species can go through major population fluctuations from year to year and that a species dominant in some years may be almost absent in others, and vice versa. Hydroperiod (the number of days in a year that a wetland holds water) is the single most important factor that influences what species are "successful" at Rainbow Bay and how these species interact. The importance of hydroperiod is clearly evident in the amphibian community. If the hydroperiod is too short, no species reproduce successfully; if too long, then only a few species may do well. The number of species successfully reproducing in the pond and the number of young emerging from the pond appear to be highest at intermediate hydroperiods. Statistical analyses show that, due to the extreme levels of natural fluctuations in amphibian numbers, long time periods (greater than 20 years) may be necessary to identify population trends, especially if changes are subtle.

In 1995, large numbers of deformed frogs were found in Minnesota, Wisconsin and Quebec. An emergency research team found frogs with missing legs, extra legs, misshapen legs, paralyzed legs that stuck out from the body at odd places and legs that were fused to the body. They also found frogs with missing eyes. One memorable specimen was a one-eyed frog that turned out to have the second eye growing inside its throat. Virtually all deformed frogs were dying quickly, because they could not feed themselves or escape from predators. The researchers believed that the most probable cause was an environmental degradation caused by some kind of chemical pollutant in water, where the frogs breed and develop, and in which they spend every stage of life.