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 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. One proposed explanation is that the decline was caused by the introduction of trout into the park’s waters, which began in 1975. (Trout are known to eat amphibian eggs.)”

Write a response in which you discuss one or more alternative explanations that could rival the proposed explanation and explain how your explanation(s) can plausibly account for the facts presented in the argument.

The author concludes that the drastic decline in amphibians in Xanadu National Park is caused by the introduction of trout into the park’s waters. The author’s reasoning is too simplistic, and there are a number of simple alternative explanations that could account for the decline in amphibians.

First, in order for trout to have caused the decline in amphibians, there would have to be trout in the park in the 1970s. The biologist who investigated Xanadu Park, John Potter, did have some trout in his aquarium, but Potter did not introduce them into the Park’s waters. He did make observations that suggested the presence of trout, but Potter’s notes are inconclusive. For instance, in 1975, Potter noticed that tadpoles of the eastern spadefoot toad could be found at the mouth of small streams. However, in 1998, Potter claimed that he did not see any tadpoles in these pools. Therefore, Potter’s observations cannot be taken as evidence that trout were present in the park in the 1970s.

Furthermore, while the presence of trout in Xanadu Park’s waters would be an explanation for why the number of amphibians declined, the explanation would not account for the decline in the number of amphibian species. Some species of frogs have very specific requirements regarding water temperature, and the presence of trout in Xanadu Park’s waters would not guarantee that the species would survive. Alternatively, the decrease in the number of amphibian species could also have resulted from the introduction of exotic species such as bullfrogs, whose numbers increased following the introduction of exotic species such as yellow perch into Xanadu Park’s waters.

The decline of amphibians in Xanadu Park could also have resulted from climate change. Warming temperatures have led to a decline in the number of amphibians worldwide, including frogs in Xanadu Park. As temperatures have risen, many species’ habitats have become inhospitable and their populations have declined. Alternatively, the decrease in the number of amphibians could also have resulted from pollution. As people continue to pollute air and water, the pollutants, such as mercury, accumulate in the food chain and lower the fertility rates of frogs. In addition, the pollutants, such as pesticides, may kill frogs by causing disease.

Finally, the decline in amphibians in Xanadu Park could also have been caused by the introduction of exotic species such as bullfrogs, whose numbers increased following the introduction of exotic species such as yellow perch into Xanadu Park’s waters. The introduction of exotic species, such as the yellow perch, could have resulted in competition between the native fish and the new invaders. The native fish may have eaten fewer of the exotic species, and the exotic species may have eaten more of the native fish. As the number of exotic species increased, the number of native fish may have decreased. The decrease in the number of native fish would have resulted in a decrease in the number of amphibian eggs because frogs lay their eggs in water. If the exotic species ate more of the native fish, then the number of eggs produced by each frog would have been reduced.

The author’s argument has some weaknesses. The biologist who investigated Xanadu Park did have some trout in his aquarium, but Potter did not introduce them into the Park’s waters. Additionally, while the presence of trout in Xanadu Park’s waters would be an explanation for why the number of amphibians declined, the explanation would not account for the decline in the number of amphibian species. Finally, the decrease in the number of amphibians in Xanadu Park could also have resulted from climate change, pollution, or the introduction of exotic species.

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