Argument150第一次，感觉这么难呢

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ARGUMENT150 - The following is a letter to the editor of an environmental magazine.

"The decline in the numbers of amphibians worldwide clearly indicates the global pollution of water and air. Two studies of amphibians in Yosemite National Park in California confirm my conclusion. In 1915 there were seven species of amphibians in the park, and there were abundant numbers of each species. However, in 1992 there were only four species of amphibians observed in the park, and the numbers of each species were drastically reduced. The decline in Yosemite has been blamed on the introduction of trout into the park's waters, which began in 1920 (trout are known to eat amphibian eggs). But the introduction of trout cannot be the real reason for the Yosemite decline because it does not explain the worldwide decline."



The editorial suggests the decline in the numbers of amphibians worldwide indicates the global pollution in water and air. He cited two studies of amphibians in Yosemite National Park to support his argument. This argument seems persuasive at first glance, however, further analysis reveals that the assumptions which the editorial based are problematic.

The threshold problem is about the results of the two studies. The author said from 1915 to 1992, the species of amphibians in Yosemite National Park declined from seven to four and the number of each species survived is also drastically reduced. The editorial fails to give us any specific statistics about how drastically reduce is, it is possible that the decreasing is normal and acceptable. Also, we are not informed whether two studies were conducted in a same way, if the methods of each study are different, then the results cannot be compared.

Even assuming that amphibians in Yosemite National Park significantly reduced, it maybe just the introduction of trout into the park's waters be blamed. Trout are known to eat amphibian eggs as the author said, then the decreasing of amphibians is the consequence of natural competition. If the water is heavily polluted, why the trout in Yosemite National Park's waters are not extincted? The trouts are even more sensible to the water pollution.

The author unfoundedly claims the amphibians' decline in worldwide makes introducing trout into the park is not the reason for it, however, the author fails to provide any evidence to substantiate this claim. Without reliable statistics about the worldwide amphibians distinction, we cannot believe amphibians are becoming to extinction.

Even assuming that amphibians are at the danger, the author fails to account other possible alternative explanations for this phenomenon. For example, the predators of amphibians such as snake, is increasing, and they consumed numerous of amphibians to feed themselves and their youngs. Or maybe the global warming caused the climate change extincted amphibians. Without ruling out these and other possible alternatives, the claim that air and water pollution should be blamed for the decline of numbers of amphibians.

In sum, without substantiated how the two studies are taken and lack of reliable statistics about amphibians worldwide, the author's argument is unpersuasive.



xdjm，一般要写多少字呀？