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本帖最后由 lynnuana 于 2010-4-6 01:16 编辑
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."
Does the decline in the numbers ofamphibians worldwide represent the global pollution of water and air? The arguer claims so in the letter, with the evidences of two studies of amphibiansin a national park—Yosemite in California. Meanwhile, he refutes to ascribe theplunge of amphibians in Yosemite to the introduction of trout. In his view, the threat of trout, because it fails to explain the worldwide decline, could notbe the real reason for amphibians decline in Yosemite. However, with manifestly unfounded grounds and perplexing statement,this argument seemscompletely untenable.
First of all, the author asserts two studies of amphibians in Yosemite to prove that worldwide amphibians decline reflects the global pollution of water.Unfortunately, the absent of the significant details in the two studies make his assertion unconvincing. How do the scientists conduct the studies? Are the two studies only towards the number of amphibians? Or are the samples of theanimals healthy and representative? The less information the author provides,the less reliable his conclusion is; let alone no information offered.
Second, the reasons of the descent in the numbers of amphibians are various.Pollution of water and air may be an important, but not the only one aspect.Perhaps these amphibians were moved from other lands which are totally different from Yosemite Park in environment. If so, habitat loss would resultin gradual extinction of the animals. Or perhaps some external causes like infectious disease, drought and war in California have ever killed most of the amphibians. Moreover, perhaps these species are under the biologic evolution.In this process, from the year 1915 to 1992, some species lost their lives while the fittest survived. Without considering these factors, the author cannot conclude that only water and air pollution should be responsible for thedecline of amphibians in Yosemite.
Third, the claim that the introduction of trout would be the real reason for the Yosemite decline still needs to be investigated. On one hand, No evidence reveals whether the number of the trout is increasing or not. If the trout in the water are also declining, then we have every reason to believe that the water must have been polluted. On the other hand, it is highly possible that the trout have lost the ability of predation and eventually lost the interestin eating amphibian eggs; because in most of park, the predators and preys are always fed separately.
Finally, even if that pollution caused Yosemite’s amphibian decline is true,the single sample is inefficient to confirm the author’s conclusion in the first sentence. Yosemite cannot represent the whole world. To strengthen hisargument, he must provide additional samples from diverse geography regions inthe world. Otherwise, no one would accept such a groundless viewpoint.
Numbers of species are in danger of extinction in every moment. I appreciate the author’s concern about the decline in the numbers of amphibians, yet his statement on the reasons of the decreasing is incomprehensive and even confusing. Such an analysis would mislead the public opinion and to some extent, accelerate loss of species of amphibians if put into practice.
--lynn 4.5
update
汤:“(不是很明白作者这一段的立场是什么,原文里是否认鳟鱼的引进是两栖动物减少----but the introduction of trout cannot be the real reason for the Yosemite decline…,但为什说the claim that the introduction of trout would be the real reason for the Yosemite decline still needs to be investigated?这样看起来好像原文是肯定鳟鱼的引进是造成两栖动物减少的真正原因了)”
lynn:你提的很对,我改了下:
Third, the claim that the introduction of trout would be the real reason for the Yosemite decline still needs to be investigated. On one hand, no evidence reveals whether the number of the trout are increasing or not. If the number of trout in the water has been growing while comparatively, that of amphibians has been declining since 1920, then we have every reason to believe that the throut are highly suspected for the descent in the park. On the other hand, it is very possible that the trout only eat the eggs of certain species of the amphibians, which is likely to be the reason that only four species left in Yosemite. Since no clue has been given on these aspects, the conclution the author makes is still open to doubt.
:00update
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