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Recent studies of the Philippine fruit bat fauna have confirmed some previous hypotheses regarding bats on oceanic islands: for example, species richness[ the number of different species in a particular area] and abundance are generally highest in the lowlands and decrease with increasing elevation. With few exceptions, each endemic species [species native to a particular place] is restricted to the modern islands that made up a single island during periods of low sea level, and genetic differentiation has been influenced by the ecology of the species and the current and past geographic and geological conditions. However, far more previous hypotheses have been overturned than supported. Some endemic Philippine species use disturbed habitat as extensively as nonendemic species that are widespread in Southeast Asia. Levels of genetic variation within all species are high, not low, and rather than showing evidence of an intrinsic vulnerability to extinction from natural causes, independent lineages of these bats have persisted in rather small areas for very long periods of time(often millions of years) in spite of frequent typhoons and volcanic eruptions. While colonization from outside areas has clearly contributed to the high species richness, speciation within the archipelago has contributed at least a quarter of the total species richness, including many of the most abundant species.

The primary purpose of the passage is to

A.draw on studies of the Philippine fruit bat in proposing a new theory regarding bats on oceanic islands
B. show how recent research on the Philippine fruit bat reflects debates about bats on oceanic islands
C. argue for the relevance of certain new evidence pertaining to the Philippine fruit bat or the study of bats on oceanic islands
D.discuss recent investigations of Philippines fruit bat in light of conventional wisdom regarding bats on oceanic islands
E.explain why the Philippine fruit bat is atypical among bats on oceanic islands in terms of genetic variation

D显示答案

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