【OG24-589题】The passage suggests which of the following about the identification of a species as a keystone species?_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).

The passage suggests which of the following about the identification of a species as a keystone species?

Such an identification depends primarily on the species’ relationship to the dominant species. Such an identification can best be made by removing the species from a particular ecosystem and observing changes that occur in the ecosystem. Such an identification is likely to be less reliable as an ecosystem becomes less diverse. Such an identification seems to depend on various factors within the ecosystem. Such an identification can best be made by observing predation behavior.

正确答案： D

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文章大意逻辑
文章开篇指出，在特定生态系统中，优势物种对生态系统的延续很关键，而“关键物种”（定义为其影响远超根据其数量所预测的物种）也能发挥重要作用。接着说明通过移除物种并观察生态系统变化来识别关键物种存在问题。然后以海獭（Pisaster ochraceus ）为例，它常是关键捕食者，因为能抑制贻贝种群，而贻贝在没有海獭时可能成为优势物种。但这种对优势物种的捕食在有或没有关键物种角色的系统中都存在。此外，海獭在不同环境（如波浪暴露和波浪遮蔽的岩石海岸）中作用不同，在某些地方沙掩埋也会影响贻贝。最后总结关键物种的地位似乎取决于特定地理环境、物种多样性、物种相互作用时长等多种因素。 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 and dominant species are crucial, keystone species also play vital role. Problem: Identifying keystone species by removal observation is problematic. Example: Pisaster ochraceus as a keystone predator, but predation on dominant species is common in different systems. Variation: P. ochraceus has different impacts in different habitats. Conclusion: Keystone status depends on context, including geography, diversity, interaction length. 做题方法及问题类型
问题类型为推断题，做题方法是根据文章中关于识别关键物种相关内容进行推断，定位提示句子如“But because complex species interactions may be involved, identifying a keystone species by removing the species and observing changes in the ecosystem is problematic.” 以及“Keystone status appears to depend on context, whether of particular geography or of such factors as community diversity and length of species interaction”等。 选项分析
A选项：文章未提及识别关键物种主要取决于其与优势物种的关系，无中生有，排除。 B选项：文中明确说通过移除物种观察变化来识别关键物种有问题，而不是最好的方法，与原文相悖，排除。 C选项：文章未表明生态系统多样性减少时识别的可靠性变化情况，无中生有，排除。 D选项：从文章提到关键物种地位取决于特定地理、物种多样性、物种相互作用时长等多种因素，可推断出识别似乎取决于生态系统内的各种因素，该项正确。 E选项：文中仅以海獭捕食为例说明问题，未表明观察捕食行为是识别关键物种的最好方法，排除。

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