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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-P448-576题】

The passage mentions which of the following as a factor that affects the role of P. ochraceus as a keystone species within different habitats?

A

The degree to which the habitat is sheltered from waves 分析A选项
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B

The degree to which other animals within a habitat prey on mussels 分析B选项
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C

The fact that mussel populations are often not dominant within some habitats occupied by P. ochraceus 分析C选项
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D

The size of the P. ochraceus population within the habitat 分析D选项
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E

The fact that there is great species diversity within some habitats occupied by P. Ochraceus 分析E选项
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当前版本由 Sunnie22 更新于2018-10-19 09:19:37 感谢由 Sunnie22 对此题目的解答所做出的贡献。

注意题目的问法，是说在 within different habitats，影响P主导地位的因素是什么，注意是在不同的栖息地，那么定位句就不应该是最后一句，而是moreover那一句，只有那一句才说了在不同的栖息地P的主导地位的变化，而最后一句只是一个笼统的说影响所有Keystone status的content。

注意题目是：affects——影响P占主导地位的因素，
文中的比较点是wave-exposed 和 wave-sheltered这个环境因素的不同。

题目讨论（6条评论）

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ziqi

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。这一句可以看出P的作用受wave shelter的影响。细节题要找到具体位置，不能笼统回答

0 0 回复 2022-04-08 16:24:45
286053m

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.

0 0 回复 2020-08-16 12:10:53
Sunnie22

注意题目是：affects——影响P占主导地位的因素文中的比较点是wave-exposed 和 wave-sheltered这个环境因素的不同

1 0 回复 2018-10-19 09:19:48
Better vivi

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, 就是这句话，做错的原因是把问题想复杂了。。。。对A项有戒备心。。。。

0 0 回复 2018-05-17 20:57:49
xiaoyi

within different habitats

0 0 回复 2017-02-06 21:36:06
yanhairiluo113

从文中可知，P物种的基石物种的地位跟地点有关 A正确，符合文中意思 B错误，没有谈及地点 C错误，同上 D错误，与“种群大小”无关 E错误，与“种群的多样性”无关

0 0 回复 2015-11-10 20:58:38