The reasons listed in the letter seem supportive to the arguer’s conclusion that the declination of the number of amphibians around the world suggests the global pollution of water and air. However, a careful examination of this letter would reveal how unfounded it is.
The most severe problem with this letter is that the arguer fails to establish a causal relationship between the decrease of the amphibians’ number and the global pollution of water and air. The pollution of the water and air may lead to the declination of the number’s of animals living on the earth, for worse living condition----more poisonous materials dissolved in the water harmful to the digestive system of wild animals fed on natural water supply, polluted air bad for their respiration system-----set more difficulties for wild animal to live as comfortable as hundreds of centuries ago. But it does not make it reasonable in the reversed way that a certain kind of animals’ declination in its number, amphibians as mentioned in the letter, should be blamed on the global pollution of air and water. Considering the relative good living condition in a national park, it is quite possible that the pollution is not the main factor which should be responsible for the number of amphibians decrease. To express it in another way, there might be some other factors making for the decline, such as the increasing number of amphibians’ natural enemy in that region or drought occurred in several years before 1992 which means less food supply and worse living condition for amphibians.
Another problematic point of the letter is its hasty generalization. Only two studies of the amphibians in Yosemite National Park is too inadequate to draw the conclusion that the number of amphibian has been declining worldwide. As known to all, any natural science research is based on a large quantity of data coming from aboard survey in various circumstances. The arguer only represents the data of the two studies in Yosemite National Park, which could be taken as a sample of North America. How could we draw any conclusion about the global situation without any data collected from other regions around the world suitable for amphibians to live in?
Although the arguer intend to rule out the possibility that the introduction of trout has caused the decline of the amphibians population in Yosemite National Park, there is no convincing evidence offered. It could be a well-founded argument if the arguer were to provide information to verify the impossibility that there is only trout who takes amphibians eggs as food.
In summary, the conclusion lacks credibility because the letter does not offer cogent evidence to support what the arguer maintains. To strengthen the argument, the arguer would have to provide information to establish the causal relationship between the pollution of water and air all over the world and the decline of amphibian population. To better evaluate the argument, more representative data should be offered support the worldwide decline of amphibian population.