The Decline of the Amphibians
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During the last 20 years, scientists worldwide have begun to notice some disturbing trends among amphibian populations. Moreover, the most troubling changes have occurred within the last decade. It seems that certain of the globe's 5,130 amphibian species have rapidly declined in number. Several species, in fact, may have already become extinct. To date, researchers do not know the reasons for this occurrence. However, some believe that atmospheric ozone depletion is responsible for the animals' decline. It could be that different amphibian species are highly vulnerable to ultraviolet radiation. Regardless of the underlying mechanisms though, the amphibians' plight may have serious implications. As "indicator" species, their decline could foretell major future environmental problems. Although amphibian population declines were first observed during the 1970s, they did not receive widespread attention until relatively recently (7:422-424). In 1989, scientists at the International Herpetologists Congress noticed an abundance of reports on amphibian declines, and even complete disappearances. Moreover, the researchers observed that the phenomena were occurring on a global scale. In the last several years, amphibian population decreases have been reported in eastern and western Canada, the western United States, the southeastern U.S., France, Italy, Central America, South America, and Australia (8:1694). Furthermore, the magnitude of
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al factors (1:1034)." McMahon and other researchers believe that such things as habitat destruction are causing population declines in many types of plants and animals--not just the amphibians. As he has said, "Amphibians species are going extinct, but so is everything else (1:1034)."
One particularly influential study performed by Pechmann et al. (1991) concluded that it may be difficult to distinguish natural population fluctuations from human-caused declines (6:895). From 1978 to 1990, the researchers gathered census data for three salamanders species and one frog species. The data were obtained at a breeding pond on the U.S. Department of Energy's 780-kilometer Savannah River Site in the upper coastal plain sandhills of South Carolina. The pond was approximately 1 hectare in size, with a maximum water depth of 1.04 meters. Typically, the pond filled in the winter, and dried the following spring or summer. In this protected environment, amphibians were censused using terrestrial drift fence and pitfall traps as they migrated to the pond on rainy nights for breeding.
Pechmann et al. (1991) observed that, from year to year, amphibian breeding population sizes fluctuated over three orders of magnitude, and juvenile recr
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Approximate Word count = 2277
Approximate Pages = 9 (250 words per page)
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