Day 83 In 1975 a wildlife census found that there were seven species of amphibians in Xanadu National Park, with abundant numbers of each species

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.

五问：

（1）“The decline of amphibians in Xanadu National Park, however, almost certainly has a different cause”是结论，其余部分是事实，值得反驳吗？

（2）1975年与2002年的两次调查是否可以用于对比呢？你能否尝试罗列一下：哪些因素的不一致可能会导致两次调查不能被比较？（比如：第一次调查时有七种 amphibians被发现，而第二次调查时只有四种 amphibians被“观测”到——我们能简单地说没有被观测到的 amphibian就一定不存在吗？）

（3）我们能否简单地判断“世界”范围内 amphibians数量的减少与Xanadu National Park内的 amphibians数量减少是毫无关系的吗？ global pollution of water and air是否应该属于全球性的影响？是否也会对 Xanadu National Park有所影响？原文中是否讨论了这个因素？

（4）原文中所提及的 trout的特点是 eat amphibian eggs，但是是否给出了足够的信息证明这些被吃掉的 eggs就是减少的 amphibians的 eggs？是否有可能 trout的数量并没有多到足以使 amphibians大量减少？

（5）即便引入 trout是 amphibians减少的一个原因，那文中有没有说明这个原因的唯一性？重要性？是否可能有其他的原因？比如：食物链遭到破坏、传染性疾病爆发等。