There have been numerous well-documented extinctions of indigenous species caused by
the introduction of nonindigenous 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 nonindigenous 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 introduced plant species. The scarcity
of documented extinctions caused by 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 nonindigenous species.
1. The passage is concerned primarily with
A. Pointing out that a particular type of species extinction is rarely known to occur
B. Proposing a possible explanation for conflicting data about a particular type of species
extinction
C. Resolving a debate about the frequency of a particular type of species extinction
D. Comparing two theories regarding possible causes of a particular type of species extinction
E. Refuting a proposed explanation for the increasingly rare occurrence of a particular type of
species extinction