The following is a letter to the editor of an environmental magazine.

“In 1975 a wildlife census found that there were seven species of amphibians in Xanadu National Park, with abundant numbers of each species. However, in 2002 only four species of amphibians were observed in the park, and the numbers of each species were drastically reduced. There has been a substantial decline in the numbers of amphibians worldwide, and global pollution of water and air is clearly implicated. The decline of amphibians in Xanadu National Park, however, almost certainly has a different cause: in 1975, trout — which are known to eat amphibian eggs — were introduced into the park.”

Write a response in which you discuss what specific evidence is needed to evaluate the argument and explain how the evidence would weaken or strengthen the argument.

The author of this letter to the editor presents a strong case for the contention that pollution is to blame for the decimation of amphibians worldwide. The environmental magazine, though, has raised some concerns, particularly pertaining to the possible cause of the decimation of the amphibian population in Xanadu National Park.

The author states that in 1975, trout were introduced into the Xanadu National Park, and that trout are known to eat amphibian eggs. This, he implies, is the reason that the amphibian population of the park has been decimated. The author states that in 2002, only four species of amphibians were observed in Xanadu National Park. He goes on to state that globally, the amphibian population has drastically declined, and that the introduction of trout into the park was a likely contributing factor. The author does not specify what type of pollution is affecting amphibian populations, but he does cite an increase in pollution levels as evidence that this pollution is to blame. The implication, though, is that pollution is to blame for the decimation of amphibian populations worldwide, and that Xanadu National Park is an isolated incident.

However, it may be that Xanadu National Park is an exceptional case. It may be, for example, that the introduction of trout into the park had a detrimental effect on amphibians, but that the restrictions imposed on fishing in the park have prevented subsequent increases in pollution levels. Additionally, the introduction of trout into the park may also have been an attempt to provide a food source for the park’s many tourists, or it may have been an attempt to reintroduce native species to an area of the park that had significantly reduced its biodiversity. It is also possible, though, that the introduction of trout into the park was a deliberate attempt to establish a sustainable ecosystem, and that the introduction of native species has exacerbated the pollution problem. Perhaps the introduction of non-native species has rendered the park’s ecosystem more susceptible to pollution, resulting in the rapid decline of amphibian populations.

Another concern raised by the magazine relates to the possibility that Xanadu National Park has simply been the victim of natural occurrences. At first glance, it may appear that the introduction of trout into the park was a deliberate attempt to introduce a non-native species into an already established ecosystem, and that the introduction of trout into a park that has previously been inhabited by native species would be likely to cause the decimation of the remaining native species. However, it may be that the introduction of trout into the park was a natural occurrence that was simply never noticed. For example, it is possible that the native species did not have the chance to reproduce, since the introduction of trout into the park reduced the population of native species, rendering them unable to reproduce. Additionally, it may be that the introduction of trout into the park was part of a natural process. For example, the trout may have entered a lake or stream that was previously inhabited by native species and moved to another body of water, where the native species eventually recolonized. It would be challenging to prove without further research whether or not the introduction of trout into the park was a natural occurrence.

The author’s suggestion that pollution is to blame for the decimation of amphibian populations around the world is compelling, but his argument leaves much to be desired. As the reader, it is difficult for me to assume that the decimation of amphibian populations in Xanadu National Park was caused by pollution, and without any evidence to support this assumption, I am inclined to doubt the validity of the argument.

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