今天为大家带来的是，GRE阅读题目解析:大象物种变小

　　P6

　　During the Pleistocene epoch, several species of elephants isolated on islands underwent rapid dwarfing. This phenomenon was not necessarily confined to the Pleistocene, but may have occurred much earlier in the Southeastern Asian islands, although evidence is fragmentary. Several explanations are possible for this dwarfing. For example, islands often have not been colonized by large predators or are too small to hold viable predator populations. Once free from predation pressure, large body size is of little advantage to herbivores. Additionally, island habitats have limited food resources, a smaller body size and a need for fewer resources would thus be favored. Interestingly, the island rule is reversed for small mammals such as rodents, for which gigantism is favored under insular conditions.

　　1. The primary purpose of the passage is to

　　A. question the plausibility of one explanation sometimes offered for the dwarfing of certain species living on islands

　　B. argue that dwarfing of certain species living on islands occurred prior to the Pleistocene

　　C. cite evidence suggesting that dwarfing may have adverse consequences for some species living on islands

　　D. present some possible explanations for the dwarfing of certain species living on islands

　　E. contrast the effects of insular conditions on species with large body size and species with small body

　　2. According to the passage, which of the following statements about body size in mammals is true?

　　A. A large body is unfavorable to mammalian species’ survival under most conditions.

　　B. A large body tends to benefit small mammals living on islands.

　　C. For most herbivorous mammals, a large body size is easier to sustain in the absence of large predators.

　　D. Under most conditions, a small body is less beneficial to herbivorous mammals than to nonherbivorous mammals.

　　E. Among nonherbivorous mammals, a small body is more beneficial on an island than on a mainland.

　　P6

　　1

　　During the Pleistocene epoch, several species of elephants isolated on islands underwent rapid dwarfing.

　　更新世中，一些与外界隔绝的岛上的大象物种，迅速变得矮小。

　　(Pleistocene 【'plīs-tə-ˌsēn】

　　更新世 [Pleistocene epoch]

　　构成地球历史的第四纪的两个世中较早的也是较长的一个世。始于约180万年前，约1万年前结束。前面是第三纪的上新世，后面是全新世。在更新世冰期，地球上超过30%的大陆面积被冰川覆盖;在间冰期，大约只有10%被覆盖。更新世的动植物开始和现代动植物相似。显花植物增多，出现新的大陆哺乳动物，如人类。该世结束时，出现了生物的大量灭绝：北美有30多种大型哺乳动物在2,000年之内消亡。在猜测出的许多原因中，最可能的两个是气候和环境的变化，以及生态模式为早期人类所破坏。

　　(大英袖珍百科)

　　dwarf (vi.)变得矮小，(vt.)令 … 停止发育，(通过对比)令 … 显得矮小)

　　2

　　This phenomenon was not necessarily confined to the Pleistocene, but may have occurred much earlier in the Southeastern Asian islands, although evidence is fragmentary.

　　这种现象并不必然局限于更新世，而可能很早以前，就在东南亚岛屿发生过，尽管目前证据尚不完整。

　　3

　　Several explanations are possible for this dwarfing.

　　对于这种矮小化现象有一些可能的解释。

　　4

　　For example, islands often have not been colonized by large predators or are too small to hold viable predator populations.

　　比如说，岛屿通常没有大型掠食者栖息，或岛屿太小不足以供养掠食者繁殖。

　　5

　　Once free from predation pressure, large body size is of little advantage to herbivores.

　　一旦失去了被掠杀的压力，大体型对植食动物是没有好处的。

　　6

　　Additionally, island habitats have limited food resources, a smaller body size and a need for fewer resources would thus be favored.

　　另外，岛上动物的食物来源有限，体型小且吃得少因而具有优势。

　　7

　　Interestingly, the island rule is reversed for small mammals such as rodents, for which gigantism is favored under insular conditions.

　　好玩的是，对于岛上栖息的，诸如啮齿动物这样的小型哺乳动物，规律正相反，巨型化更适应岛上条件。

　　1. The primary purpose of the passage is to

　　A. question the plausibility of one explanation sometimes offered for the dwarfing of certain species living on islands

　　B. argue that dwarfing of certain species living on islands occurred prior to the Pleistocene

　　C. cite evidence suggesting that dwarfing may have adverse consequences for some species living on islands

　　D. present some possible explanations for the dwarfing of certain species living on islands

　　E. contrast the effects of insular conditions on species with large body size and species with small body

　　选 D

　　为某些岛上栖息的物种的矮小化，提供了一些可能的解释。

　　2. According to the passage, which of the following statements about body size in mammals is true?

　　A. A large body is unfavorable to mammalian species’ survival under most conditions.

　　B. A large body tends to benefit small mammals living on islands.

　　C. For most herbivorous mammals, a large body size is easier to sustain in the absence of large predators.

　　D. Under most conditions, a small body is less beneficial to herbivorous mammals than to nonherbivorous mammals.

　　E. Among nonherbivorous mammals, a small body is more beneficial on an island than on a mainland.

　　选 B

　　根据在句 7：

　　Interestingly, the island rule is reversed for small mammals such as rodents, for which gigantism is favored under insular conditions.

　　A 错在 most，句 5 就暗示，有掠食者时，大体型对植食动物有好处。

　　C 错。无论什么条件下，体型大都比体型小更难 sustain，只不过有被掠杀危险时，植食动物宁可付出更大成本，使自己体型变大，来抵消一部分被掠杀的风险。

　　D 错。未知信息，文中从未讨论过 nonherbivorous mammals 的体型。

　　E 错。未知信息，理由同 D 。

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