ARGUMENT69 by zephyrqq

zephyrqqUID: 2260290

ARGUMENT69 - Yellow-legged frogs were once common in high-altitude lakes in the Sierra Nevada mountains, but they have become increasingly rare. Trout feed on tadpoles and young frogs. Few lakes in the Sierra Nevada had any trout in them until a hundred years ago. At that time, many lakes were stocked with trout for recreational fishing, and now trout are common in virtually all bodies of water in the Sierra Nevada. Researchers removed the trout from one lake, and the frog population soon quadrupled. Since frogs are capable of moving several miles over land, removing trout from just a few lakes is clearly the way to restore the frog population to its former levels.

字数：435   589       用时：00:45:00    加15分钟    日期：2008-2-22 22:28:38


Before accepting the author's suggestion that we can restore the frog population to its former levels by removing trout from just a few lakes in the Sierra Nevada mountains, we should reflect on the reasons given by the author once more. The reason is that there is that the are some logic fallacies which would prevent us from taking the author's recommendation seriously.

To begin with, the author fails to convince us that it is the existence of trout that cause the rarity of frogs. However, what if the frogs had already become rare before the Sierra Nevada introduced trout. If this was exactly the case, the decline of  frogs certainly had nothing to do with trout. Moreover, he simply neglect other factors that might also be responsible for the same consequence. For example, it is possible that a considerable quantity of frogs had been caught by local hunters for commercial purpose. Or perhaps this area became open to tourism and therefore the recreational activities of human beings such as fishing and boating actually have disturbed the ordinary living of frogs and threaten their survivals. Any of the scenarios, if true, would undermine the author's assumption that it is trout that lead to the rarity of the frogs.

Furthermore, the experiment that after researchers removed the trout from one lake, the frog population soon quadrupled lend less support to the assumption that this favorable thing would happen in other lakes with the same treatment. The author commits a false analogy and takes it for grated without justification that the situations of other lakes in this area are the same as the researched one. Actually, this is not necessarily the case. Without the help of relevant information, we could not ruling the possibility that in some of these lakes the frogs are faced with some natural enemies besides trout, and these natural enemies could do more harm than trout could do to their existence. Or perhaps the researched lake is a relatively clean one, and other lakes, which have been seriously polluted, could not be a suitable residence for the frogs any more. Without excluding these possibilities, we do not think the method which can work well in just one lake can be successfully applied to other lakes.

Finally, even assuming that trout lead to the decrease of the frog and we can protect frogs by removing trout, the fact that frogs are able to move several miles over land could not be view as a compelling reason for the author's policy. The author might assume that the frogs could know the location of "safe" lakes free of trout and then them would migrate to these lakes. Nevertheless, no evidence show the frogs are so intelligent.  In addition,  since trout  feed on tadpoles and young frog, it is entirely possible that trout might eat all the tadpoles and young frogs before the could become adult frogs. Common sense tells us that only adult frogs could move on the land for a long time. Thus, even if they are clever enough to know where the safe places are, they have no opportunity to arrive. So we cannot accept the author's conclusion that by removing trout from just a few lakes we can restore the frog population to its former levels.

For all these reason, this argument is unsubstantial as it stands. To better assess it, we need more information about  the reason why the frog population decreased. And other date about the circumstance in all the lakes will also be helpful.

[ 本帖最后由 zephyrqq 于 2008-3-6 19:15 编辑 ]