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Canaries in Our Wetlands Globally over 200 amphibian species have experienced recent population declines with reports of 32 species extinctions. The answer as to the cause of these declines is a complicated one due to the many factors involved. In this article I will set out the major causes involved in the recent declines of amphibian populations and discuss a related issue, the recent increase in the number of amphibians born with malformations. Based on Collins and Storfer’s (2003) review we can separate the causes of decline into 2 major categories, the first includes factors general to overall biodiversity such as habitat destruction, introduced species, and over exploitation. The second category is more complex because it pertains to amphibians in relatively pristine environments (Collins and Storfer, 2003). This category includes such factors as climate change, UV-B radiation, and chemical contaminants. It is important to note that amphibians are extremely sensitive to changes in their environment due to their permeable skin and unshelled eggs. Therefore sudden and accelerated declines in amphibian populations and substantial deformities among them are good indicators that something is awry in the environment. Habitat destruction is a major cause of the amphibian decline. It eliminates local or regional ecosystems leading to the loss of the ecosystem’s former biological function. Habitat destruction is most obvious when amphibian habitats are drained and made into human developments. A study by Davidson et al (2002) found that habitat destruction due to urbanization has significantly contributed to the decline of the California red legged frog. Altering amphibian habitats also adversely affects the ecosystem’s function. For example overgrazing of grasslands is a serious problem for amphibians because it leads to loss of vegetation and then serious erosion. Another form of habitat destruction is habitat fragmentation, which happens principally when one cohesive area that amphibians occupy is separated into several smaller habitats due to destruction of the linking area. The effects of fragmentation are dire, for example remaining populations are isolated from each other and are more likely to go extinct in the long run than are those populations which are connected (Bradford et al. 1993). Habitat fragmentation can lead to the loss of diversity within the gene pool which affects the population’s ability to respond to environmental changes. Therefore destruction of original habitat works synergistically with other factors that I will discuss such as chemical contaminants, climate change and introduced species because of the lack of genetic diversity. A second threat to amphibian populations is over exploitation. Amphibians are collected all over the world for consumption as food, use as fishing bait, pets, and subjects in laboratory studies. Frog legs are eaten all over the world, from China to the U.S.A. Between 1981 and 1984 the U.S. alone imported more that 6.5 million pounds of frog legs, which is equivalent to about 26 million frogs (Jensen et al. 2003). This significant commercial demand is leading to the over harvesting of frogs all over the world.
Approximate Word count = 1967
Approximate Pages = 7.9
(250 words per page double spaced)
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