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OG18官方指南,建议同学们刷3遍。第一遍做题了解题型和考点,第二遍精刷,第三遍集中解决疑难问题。建议考生第一遍刷题采用官方正版纸质书籍,若遇到疑难问题,欢迎在此专区查阅解析,提供解析,参与题目讨论,与所有考生一起解决疑难问题。
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While the most abundant and dominant species within a particular ecosystem is often crucial in perpetuating the ecosystem, a "keystone" species, here defined as one whose effects are much larger than would be predicted from its abundance, can also play a vital role. But because complex species interactions may be involved, identifying a keystone species by removing the species and observing changes in the ecosystem is problematic. It might seem that certain traits would clearly define a species as a keystone species; for example, Pisaster ochraceus is often a keystone predator because it consumes and suppresses mussel populations, which in the absence of this starfish can be a dominant species. But such predation on a dominant or potentially dominant species occurs in systems that do as well as in systems that do not have species that play keystone roles. Moreover, whereas P. ochraceus occupies an unambiguous keystone role on wave-exposed rocky headlands, in more wave-sheltered habitats the impact of P. ochraceus predation is weak or nonexistent, and at certain sites sand burial is responsible for eliminating mussels. Keystone status appears to depend on context, whether of particular geography or of such factors as community diversity (for example, a reduction in species diversity may thrust more of the remaining species into keystone roles) and length of species interaction (since newly arrived species in particular may dramatically affect ecosystems).

【OG20-P449-578题】

Which of the following, if true, would most clearly support the argument about keystone status advanced in the last sentence of the passage?

  • 分析A选项
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  • 分析B选项
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  • 分析C选项
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  • 分析D选项
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  • 分析E选项
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该题目由网友Nyp4wMdW提供。更多GMAT题目请
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当前版本由 ya**** 更新于2015-11-10 20:59:43 感谢由 ya**** 对此题目的解答所做出的贡献。
逻辑支持题,作者的论点为是否是基石物种要看环境
A错误,没提及上述因素
B正确
C错误,没提及上述因素
D错误,没提及上述因素
E错误,没提及上述因素
当前版本由 Sunnie22 更新于2018-10-19 09:33:16 感谢由 Sunnie22 对此题目的解答所做出的贡献。

答案点:for example, a reduction in species diversity may thrust more of the remaining species into keystone roles
说明diversity↓  →  ↑specie成为keystone
B ————邻岛species多,diversity大,所以不是keystone;本岛之所以有keystone,是species较少的原因。

当前版本由 Yang1116 更新于2018-10-08 19:05:34 感谢由 Yang1116 对此题目的解答所做出的贡献。

最后一句想表达的就是各种因素变化对role的影响,只有B变现出来因为某些(地理)因素的改变,而造成role的改变;


题目讨论 2条评论)

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    847716opn

    选项意思没读懂。context与geography,community diversity和length of species interaction有关。A是两个物种之间的interaction。B是同一物种在不同的环境的地位不同-geography。C人类观察 D keystone越多,对环境影响越大。Emoth会掩饰自己是potential。
    0 0 回复 2019-09-27 09:16:28
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    河边柳青青

    。。。最后一句说影响一个物种作为keystones有可能是一个特定的地理环境,也可能是物种的密度。
    B选项说i在一个地方是ks,但在另一个地方由于受到另一种群数量过大的影响,而不能成为ks。
    虽然我觉得A好像也在说种群密度的事。。。难道是因为A没有说KS??
    0 0 回复 2017-10-22 19:39:33
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      四圈回复河边柳青青

      最后一段说的diversity是多样性的意思呀,是种类的问题。密度是density,两个词有点像

      0 0 回复 2018-01-02 11:54:52

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