Argument150 附提纲，敬请大家随便拍，必回拍

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150The 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."
1.        加州Y公园里两栖动物的数目和种类是否真的减少
2.        无法无准确证据表明Y公园空气水质污染，而且这种情况造成了两栖动物数量的减少；无法排除鲑鱼对Y公园的影响；忽略了其它原因（气候，天敌，食物等）
3.        不具备推广性

In the letter, by quoting the two studies in Yosemite National Park (YNP) the author conclude that global air and water pollution result in the decrease of amphibians. It seems well-presented, however the ratiocination suffer from some logical flaws since the author fails to take into account other possibilities.

To begin with, the author does not provide sufficient data to prove the credibility of two studies in YNP. Whether two studies are conducted by the same authority in this area and executed in the same season? If the study in 1915 was render by scientists equipped with completed facilities while the study in 1992 was provided by a group of amateurs without enough tools. Moreover, it is highly possible that the former study was carried out in summer when almost all amphibians are active outside, while the latter study was implemented in winter when amphibians are in habitation, so that most of them could not be detected by people. If so, possible the species and the number of amphibians in YNP do not decline actually. That is to say, the evidence cannot bolster author’s conclusion well.

In addition, even if we concede the decline of amphibians in YNP, the author has not enough solid information to assure the root cause is the polluted water and air. First of all, the author does not afford scientific data to demonstrate the water and air was polluted. Without the detailed comparison data from 1915 to 1992, such as the sorts of mineral contained in the water and the percentage of noxious gas in air, it is hard for us to believe that the quality of water and air has declined drastically so that it is unfit for the living of amphibians. Secondly, the author has not powerful evidence to rule out the influence of the introduction of trout and cannot explain why trout known to eat amphibian eggs do not responsible for the decline of amphibians in YNP. Last, the author fails to consider other alternatives which could result in the decrease of amphibians in YNP, such as frequently fluctuating temperature, lack of adequate food or the increase of natural enemy.  

Last but not least, concession granted the root cause of decline of amphibians in YNP is the polluted water and air; it is too harsh and presumptuous to generalize sweepingly to the worldwide. We are non informed that YNP is enough representative to reflect the whole condition in the world. The author fails to convince us that the primary reasons of decline of amphibians in other places are similar or same as that of YNP.

In sum, based on what has discussed above, it is obvious that the evidence cannot sustain author’s conclusion effectively. In order to make it more convincing, the author should rule out other possibilities and prove the inverse correlation between levels of air and water pollution and amphibian populations worldwide.