【OG24-587题】Which of the following hypothetical experiments most clearly exemplifies the method of identifying species, roles that the author considers problematic?_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 hypothetical experiments most clearly exemplifies the method of identifying species, roles that the author considers problematic?

A population of seals in an Arctic habitat is counted in order to determine whether it is the dominant species in that ecosystem. A species of fish that is a keystone species in one marine ecosystem is introduced into another marine ecosystem to see whether the species will come to occupy a keystone role. In order to determine whether a species of monkey is a keystone species within a particular ecosystem, the monkeys are removed from that ecosystem and the ecosystem is then studied. Different mountain ecosystems are compared to determine how geography affects a particular species, ability to dominate its ecosystem. In a grassland experiencing a changing climate, patterns of species extinction are traced in order to evaluate the effect of climate changes on keystone species in that grassland

正确答案： C

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文章大意逻辑
文章先指出在特定生态系统中，丰富且占主导地位的物种对生态系统的延续很关键，同时“关键物种”（定义为其影响远大于根据其数量所预测的物种）也很重要。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，阐述其作为关键捕食者的作用，以及关键物种地位会受地理环境、物种多样性和物种相互作用时长等因素影响。 文章类型及逻辑简图
文章类型：观点阐述型。逻辑简图： Main idea: Keystone species play a vital role in ecosystem, but identifying them by removal observation is problematic. Example: Pisaster ochraceus as a keystone predator. Factors affecting keystone status: geography, species diversity, species interaction length. 问题类型及做题方法
问题类型：推断题。做题方法：根据文中“identifying a keystone species by removing the species and observing changes in the ecosystem is problematic”这一定位提示句子，判断选项中哪个实验体现了这种有问题的识别方法。 选项分析
A选项：统计北极栖息地海豹数量以确定其是否为优势物种，未涉及移除物种，不符合有问题的识别方法，排除。 B选项：将一个海洋生态系统中的关键物种引入另一个海洋生态系统，不是移除物种观察原生态系统变化，不符合，排除。 C选项：为确定某种猴子是否为关键物种，将猴子从特定生态系统中移除然后研究该生态系统，符合文中提到的有问题的通过移除物种来识别关键物种的方法，当选。 D选项：比较不同山地生态系统以确定地理对物种主导能力的影响，未涉及移除物种，排除。 E选项：在经历气候变化的草原追踪物种灭绝模式以评估气候变化对关键物种的影响，未涉及移除物种，排除。

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