The following is a letter to the editor of an environmental magazine."Two studies of amphibians in Xanadu National Park confirm a significant decline in the numbers of amphibians. In 1975 there were seven species of amphibians in the park, and there were

The argument above is well-presented and appears to be relatively sound at first glance: since the fewer number of amphibian species were observed in the second study, it seems plausible to argue that it was caused by the introduction of trout. However, as more light is shed on the issue and more detailed facts are concerned, the possibility of alternative explanations leads me to question the validity of the argument.

To begin with, the author needs to take account of alternative explanation for the different number of amphibians in each study. It is entirely possible that the first study was conducted for one year and the second study was conducted for a week. In this case, the second study observed fewer amphibians not because they actually reduced, but because the researchers did not have enough time to find them due to the time restriction. Also, it is plausible that the first study may have been conducted by a group of experts in the field and the second study was done by a group of college students specializing in a completely different field. If this were the case, it is more likely that the experts would have found more species of amphibians because of their expertise and knowledge compared to the amateurs.

Another alternative explanation for the credibility of the second study should be taken into consideration. The author states that the number of species decreased; however, it is likely that the numbers of amphibians did not actually reduce. Instead, the researchers simply may not have been able to find the amphibians. Since the argument states that the number of amphibians “observed” decreased, this does not indicate that they declined in actuality. Also, without detailed statistics on the decline, in all likelihood, the amphibians in the second study may not have drastically reduced. In this case, the difference of the number of amphibians in 1975 and 2000 is negligible, the so-called reduction may not be significant.

Lastly, the author needs to consider possible alternatives besides the contribution of Trout on the reduction in amphibian species. In all possibility, the amphibians decreased not because of the introduction of the trout, but because of other factors, such as humans, an environmental factor, or lack of food. Moreover, the reduction may not be contributed to other factor. One of the aforementioned factors may go hand-in-hand with the introduction of trout.

In conclusion, the aforementioned argument is not cogent on many grounds. To bolster the assertion, the author should rule out all the possible explanations mentioned above.