Some Populations Are Stable

In contrast to these reports of declines, other studies have found that some amphibian populations are stable. For example, researchers studying amphibians in the Canadian province of New Brunswick over several years found no evidence that any species there have declined in number. And studies since the early 1980's at the Savannah River Ecology Laboratory, affiliated with the University of Georgia, have discovered that amphibian populations on the Georgia-South Carolina border undergo considerable fluctuations. But the researchers have found no indications that any of the populations in the area are in permanent decline.

Some studies have obtained contrasting results by looking at different populations of the same species. For example, in North America, studies indicate that northern populations of Blanchard's cricket frogs have declined, while southern populations have remained robust. Such studies underscore the fact that amphibians in different regions confront different environmental conditions. In addition, within particular regions, some species of amphibians may be in decline while others are stable. Although researchers have documented cricket frog declines in the upper Midwest, many other amphibian species that share the cricket frog's wetland habitat in the region appear to be doing well. These sorts of findings indicate that different amphibian species respond in their own individual ways to the same kinds of environmental influences.

While some researchers are studying trends in amphibian populations, other investigators are focusing on amphibian malformations. The phenomenon of amphibians with various kinds of physical abnormalities came to national attention in 1995, when a group of Minnesota students discovered hundreds of deformed frogs during a field trip to a wetland. Soon, other reports of malformed amphibians were being reported from many parts of the United States and Canada. Malformations have also been reported from Japan. Observed deformities have included misshapen, extra, or missing limbs; missing or shrunken eyes; and abnormally small sex organs. The relationship between amphibian population declines and amphibian malformations--if any--was still unclear in 1998. Observers have seen malformations in amphibian populations that appeared to be stable, and they have noted a decline in numbers among many amphibian populations that have no malformations.

An analysis of the various studies done in the 1980's and 1990's has led most biologists affiliated with the DAPTF to conclude that amphibians in many parts of the world are suffering population declines and malformations. Researchers in 1998 were trying to determine the causes of these problems. They were investigating causes both originating in nature and stemming from human activities.