0910G【Try Best】第二小组 argument150 by tianshi02

tianshi02UID: 2362794

TOPIC: 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."
WORDS: 320          TIME: 00:50:00          DATE: 2009-7-8 17:08:54

In this letter, the arguer concludes that the decrease in the numbers of amphibians in the world explicitly indicates the global water and air pollution, on the basis of two studies in Yosemite National Park (YNP). However, the two studies lend little support to the conclusion.

The primary flaw in this argument is that the studies in YNP don't tell us much about the correlation between the reduced number of amphibians and the global pollutioin. That is because in YNP trout is introduced, which is not the case elsewhere in the world. Moreover, trout are known to influence amphibian numbers. No conclusion can be drawn on the global ecosystems, unless the impact of trout on amphibian numbers are shown nonexistent. It is presumptuous for the arguer to assume the the introduction of trout is not the real reason for the decline of amphibian numbers, without any evidence or reasoning.

Even assuming that trout has nothing to do with the decline in amphibian population,  we still cannot clearly see a causal relationship between the decline and the pollution in YNP, not to mention in the world. The arguer assumes that the popution is more severe in 1992 as compared to that in 1915, and then demonstrate a correlation between the reduced number of amphibians and the pollution. Suppose this assumption is valid, there are many other factors involved as explanations of the decline. Take for example, human intervention of the ecosystem in YNP, the climate variation and so on. Without ruling out these possible explanations, one cannot say that pollution is the major cause of decline.

Last but not least, we cannot generalize the situation of YNP to the worldwide ecosystem, which is more complicated and intricate. In the ecosystem elsewhere, the major preys and predators are probably different, the natural resourcs, such as water and air, are not exactle the same... Without accounting for such differences, any analogy is premature.

To sum up, the argument is unconvincing as it stands. To remedy the argument, the arguer is supposed to prove to us that the introduction of trout is indeed irrelevant to the decline at the first place. He/she also needs to eliminate other possible reasons for the decline and show the ecosystem is representative the worldwide ecosystems.