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 shows that the number of species of amphibians in this park were drastically reduced between 1915 to 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 aruger unfairly assumes that the introduction of trout brought no influence about the species reduce. It is possible that the trout ate much amphibian's eggs in these years and badly affects this area's eco-balance. In addition, the arguer attempts to establish a causal relationship between two matters: the amphibians reduced in Yosemite park and the global pollution of water and air. What's more, the evidence which the arguer used is the one prviousely used as a conclusion. Finally, the aruger omits several other concers that should be addressed. For example, the data about the park's temperture and humility changed between 1915 to 1992, the number of the trout in the recent years, the number of amphibians in other park between 1915 to 1992. In summary, the conclusion reached in this argument is invalid and misleading. To make the argument more convicing, the arguer would have to prove that the number of the amphibians in other park shows the same decline trendency. Moreover, I wolud suspend my judgement about the credibility of the recommendation until the arguer can provide concrete evidence that I notice before.