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: 274 TIME: 0:38:42 DATE: 2009-1-18

In this argument, the arguer concludes that the decline in the numbers of amphibians in Yosemite National Park in California indicates the global pollution of water and air. In addition, the arguer reasons that two studies show that the number of species of amphibians in this park were drastically reduced between 1915 and 1992. This line of reasoning is flawed in several aspects. First of all, as the arguer claimed, the decline in Yosemite has been blamed on the introduction of trout into the park’s waters in 1920. However, the arguer unfairly assumes that the introduction of trout brought no influence on the species reduction. It is possible that the trout ate many amphibian eggs in these years and badly affected this area’s eco-balance. In addition, the arguer attempts to establish a causal relationship between two matters: the reduction of amphibians in Yosemite Park and the global pollution of water and air. What’s more, the evidence that the arguer used is the same as the conclusion previously used. Finally, the arguer omits several other concerns that should be addressed. For example, the data about the park’s temperature and humidity changes between 1915 and 1992, the number of trout in recent years, the number of amphibians in other parks between 1915 and 1992. In summary, the conclusion reached in this argument is invalid and misleading. To make the argument more convincing, the arguer would have to prove that the number of amphibians in other parks shows the same decline trend. Moreover, I would suspend my judgment about the credibility of the recommendation until the arguer can provide concrete evidence that I noticed before.