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  3. It is usually claimed that species-rich ecosystems tend to be more stable than species-poor ecosystems. Three mechanisms by whic

It is usually claimed that species-rich ecosystems tend to be more stable than species-poor ecosystems. Three mechanisms by whic

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问题     It is usually claimed that species-rich ecosystems tend to be more stable than species-poor ecosystems. Three mechanisms by which higher diversity increases ecosystem stability have been proposed. First, if there are more species in an ecosystem, then its food web will be more complex, with greater redundancy among species in terms of their nutritional roles. In other words, in a rich system if a species is lost, there is a good chance that other species will take over its function as prey, predator, producer, decomposer, or whatever role it played. Second, diverse ecosystems may be less likely to be invaded by new species, notably exotics (foreign species living outside their native range), that would disrupt the ecosystem’s structure and function. Third, in a species-rich ecosystem, diseases may spread more slowly because most species will be relatively less abundant, thus increasing the average distance between individuals of the same species and hampering disease transmission among individuals.
    Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
选项 A、In any ecosystem, as the number of individuals in the same species increases, the rate of disease transmission slows down.
B、Ecosystems that have a small number of different species tend to be disease-free, because the species’ habitats are at a safe distance from each other.
C、In ecosystems with many species, diseases spread more slowly because there are fewer individuals in a species and, as a result, the individuals are more widely scattered.
D、The average distance between individuals in a species-rich ecosystem increases, so diseases are prevented from being communicated between species.
答案C
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