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 attributes the decline in the number of amphibians in Xanadu National Park between 1975 and 2002 to the introduction of trout into the park’s waters beginning in 1975. While trout could be the reason behind the decline, since they are known to eat amphibian eggs, the information currently available is not conclusive to qualify the proposed explanation the only one capable of elucidating the fact in the argument. Several alternative possibilities could also account for the decrease in both the number and species of amphibians.

Before considering the cause of the reduced amphibian population, we must consider the possibility that the studies confirming the decline are inaccurate. The alleged decline both in species and population could be the result of an underestimate in the 2002 investigation. For example, researchers may have only surveyed a specific area of the park where the amphibian population was particularly low and subsequently extrapolated this regional observation to the entire park. Such a methodology would lead to an ostensible decline in numbers despite the accurate numbers of each species actually remaining constant or even rising.

Even if we acknowledge that the amphibian population and number of species had dropped in the 27-year period, there are at least two explanations apart from the introduction of trout that can account for the change. The first is anthropogenic factors. For example, environmental pollution resulting from economic development in the nearby region could have adversely affected the amphibian species’ survival. Amphibians spend the first stage of their life in natural water bodies and may be very sensitive to water quality. If pollution, such as waste discharge containing toxic elements, enters the amphibian habitats, the amphibian population might decrease consequently. Another possible anthropogenic factor which may have impacted the amphibian population is hunting. Amphibians may be hunted for their medical values. If demand for amphibian-derived medicine increased between 1975 and 2002, amphibian hunting in Xanadu National Park could have intensified.

Other than human causes, natural factors may also play a role in wiping out amphibians. Drastic environmental changes, other than the presence of trout, could have occurred in the park. Climate change is a likely candidate, which would have a huge impact on amphibians because they cannot regulate their body temperature. Reduced precipitation is capable of worsening the quality of amphibian habitat as well. In these scenarios, amphibians would migrate from the park because it had become inhabitable for them.

In a nutshell, there are multiple possible explanations that can account for the decline in the amphibian population and number of species in Xanadu National Park, if the decline is accurate in the first place. However, given the limited information at hand, it is difficult, if not impossible, to determine the real cause(s). Additional information on changes in the park, both manmade and natural, during this timeframe would be helpful.

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