【OG24-588题】Which of the following, if true, would most clearly support the argument about keystone status advanced in the last sentence of the passage?_mofa留学圈mofaGRE在线题库系统_GRE在线搜题_GRE题库解析_GRE真题机经_GRE课程_GRE培训机构

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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).

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

A species of bat is primarily responsible for keeping insect populations within an ecosystem low, and the size of the insect population in turn affects bird species within that ecosystem. A species of iguana occupies a keystone role on certain tropical islands, but does not play that role on adjacent tropical islands that are inhabited by a greater number of animal species. Close observation of a savannah ecosystem reveals that more species occupy keystone roles within that ecosystem than biologists had previously believed. As a keystone species of bee becomes more abundant it has a larger effect on the ecosystem it inhabits. A species of moth that occupies a keystone role in a prairie habitat develops coloration patterns that camouflage it from potential predators.

正确答案： B

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文章大意逻辑
文章开篇指出在特定生态系统中，虽然丰富且占主导地位的物种对维持生态系统很关键，但“关键物种”（其影响远超根据其数量所预测的）也发挥重要作用。接着说明通过移除物种来识别关键物种存在问题。然后以海獭（Pisaster ochraceus ）为例，阐述其作为关键捕食者的作用。随后指出关键物种地位在不同环境有所不同，最后总结关键物种地位取决于地理环境、物种多样性和物种相互作用时长等背景因素。 文章类型及逻辑简图
文章类型为观点阐述型。逻辑简图： Introduction: Abundant dominant species crucial, keystone species also vital. Problem: Difficulty in identifying keystone species. Example: Pisaster ochraceus as a keystone predator. Variation: Keystone role varies in different habitats. Conclusion: Keystone status depends on context. 做题方法及问题类型
本题为加强论证的细节题，通过定位文章最后一句“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).”，寻找能体现关键物种地位取决于环境因素的选项。 选项分析
A选项：只说明了蝙蝠对昆虫种群以及昆虫种群对鸟类的影响，未涉及关键物种地位和环境因素的关系，不能加强，排除。 B选项：鬣蜥在某些热带岛屿是关键物种，在相邻物种更多的岛屿却不是，体现了关键物种地位取决于地理环境和物种多样性等环境因素，能加强，当选。 C选项：只是说在稀树草原生态系统中比之前认为的有更多物种是关键物种，未提及关键物种地位和环境因素的联系，无法加强，排除。 D选项：讲的是蜜蜂数量增多对生态系统的影响，没有体现关键物种地位和环境的关联，不能加强，排除。 E选项：飞蛾的伪装模式与关键物种地位和环境因素无关，不能加强，排除。

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