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

In his letter to the editor of the environmental magazine, the author avers that, despite the fact that there is a declining trend in the number of amphibians worldwide due to air and water contamination, the dwindling amphibian population in Xanadu Park is a direct consequence of the introduction of trout into the park in 1975. The author has come to this conclusion based on the fact that, according to wildlife censuses, there has been a nearly 50% reduction in the number of species of amphibians in the park –and a drastic decline in the numbers of each remaining species– between 1975 and 2002. However, before this argument can be properly evaluated, two specific pieces of evidence must be collected and analyzed.

First of all, in order to determine whether the declining amphibian population in Xanadu Park conforms to the global trend, it is necessary to evaluate the current levels of air and water pollution in the park, and whether these levels are detrimental to the amphibian population. While it is possible that the levels of pollution in Xanadu Park are lower than the global average, a slight variance in the quality of their habitat might prove deleterious to certain amphibian species. For instance, a small variation in the levels of oxygen in the water –due to contamination – might prove noxious to amphibians that spend most of their lives underwater. On the other hand, there is a possibility that the quality of air and water in Xanadu Park were severely compromised between 1975 and 2002. It may be possible that neighboring areas experienced an increase in industrial activity within the same period of time, with industrial waste and toxic emissions reaching the waters and air of the park, thereby drastically deteriorating the amphibians’ habitat. If either of these scenarios has merit, then the conclusion drawn in the original argument is significantly weakened.

Secondly, it is important to determine whether the 1975 wildlife census was performed before or after the introduction of trout into the park. The author of the letter prematurely assumes that the 1975 census does not reflect the effect that trout has on the amphibian population. However, this might not be the case. Perhaps the census took place several months after the introduction of trout into the park, with the purpose of assessing the impact of a new predatory species – the trout – on amphibian population. Granted, the author of the letter may argue that, if this were the case, the census might already reflect a sharp reduction in the number of amphibians in Xanadu Park due to trout foraging behavior. Still, while it is true that introducing a new predator will reduce the number of prey, predators will only eat enough prey to sustain their lives but they will not eat so many as to deplete their food source. If the above is true, the extinction of nearly half the amphibian species in the park cannot be directly attributed to trout, and thus, the argument does not hold water.

In conclusion, the argument, as it stands now, is considerably flawed due to its reliance on several unwarranted assumptions. If the author is able to provide the two pieces of evidence stated above and perhaps conduct a systematic research study, then it will be possible to determine whether the decline in amphibian population in Xanadu Park is strictly a consequence of introducing trout into the park.