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题库 / OG2016-RC-116
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.
题目分析：
文章推断题：文章暗示了以下哪个关于keystone的辨别？
选项分析：
A选项：这种辨别取决于物种和主导物种的关系：原文没提。
B选项：这种辨别的最好办法是把物种从生态系统中移除并且观察生态系统的变化：原文已经提到这种方法是有问题的。
C选项：当一个生态系统变得没那么多样化时，这种辨别是不可靠的：原文说当生态系统没那么多样化时，会有更多的其他物种成为keystone。
D选项：正确。这种辨别取决于生态系统中的多个因素：文章整篇都在说明定义keystone是不容易的，并举P.o的例子，来证明多个因素会影响keystone。
E选项：这种辨别可以通过观察捕食行为：原文没提。
But because complex species interactions may be involved, identifying a keystone species by removing the species and observing changes in the ecosystem is problematic. 定位
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).
全文最后一句表达了物种统治地位的发生条件：1. 地理环境 2.种群多样性 3.种群交互时间 即多重因素
D.Correct. If, as the passage suggests, keystone status for any given species depends on the context of the ecosystem in which it lives, then it is likely that identifying keystone species depends on strongly on understanding what factors of the ecosystem contribute to creating keystone status. The passage lists such factors as geography, community diversity, and species interaction. D 就相当于原文改写。。。。
B The passage explicitly states that this method of identification would be problematic.
Correct. If, as the passage suggests, keystone status for any given species depends on the context of the ecosystem in which it lives, then it is likely that identifying keystone species depends on strongly on understanding what factors of the ecosystem contribute to creating keystone status. The passage lists such factors as geography, community diversity, and species interaction.
A While the passage uses an example of a keystone species, Pochraceus, which preys on a species that would, in the keystone species’ absence, be dominant, there is nothing to suggest that a keystone species must have a particular relationship with the dominant, or potentially dominant, species in an ecosystem. 这里就是逻辑中的枚举推理中的 CQ1...
针对A，D: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.
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).