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There have been numerous well-documented extinctions of indigenous species caused by the introduction of non-indigenous predators and pathogens. However, surprisingly few extinctions of indigenous species can be attributed to competition from introduced species. For example, during the past 400 years, 4,000 plant species have been introduced into North America, and these non-indigenous plants currently account for nearly 20 percent of North America`s plant species. Yet no evidence exists that any indigenous North American plant species became extinct as a result of competition from new species could mean that such extinctions take longer to occur than scientists initially believed or, alternatively, that extinctions are rarely caused by competition from non-indigenous species.

The author introduces statistics about North America`s non-indigenous plant species primarily in order to

A undermine a proposed explanation for the absence of any evidence for the occurrence of a particular phenomenon
Bcontrast the effect of introduced plant species in North America with the effect that introduced animal species have had
Csuggest that North America`s indigenous plants are a domain in which there has been ample scope for a particular effect to have occurred
Demphasize how much the ecology of North America has been affected over the past 400 years by the introduction of non-indigenous species
E substantiate a claim about the overall effect that the introduction of non-indigenous species tends to have on indigenous populations

E显示答案

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