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  3. There are both great similarities and considerable diversity in the ecosyste

There are both great similarities and considerable diversity in the ecosyste

游客2025-01-19  22
问题     There are both great similarities and considerable diversity in the ecosystems that evolved on the islands of Oceania in and around the Pacific Ocean. The islands, such as New Zealand, that were originally parts of continents still carry some small plant and animal remnants of their earlier biota (animal and plant life), and they also have been extensively modified by evolution, adaptation, and the arrival of new species. By contrast, the other islands, which emerged via geological processes such as volcanism, possessed no terrestrial life, but over long periods, winds, ocean currents, and the feet, feathers, and digestive tracts of birds brought the seeds of plants and a few species of animals. Only those species with ways of spreading to these islands were able to undertake the long journeys, and the various factors at play resulted in diverse combinations of new colonists on the islands. One estimate is that the distribution of plants was 75 percent by birds, 23 percent by floating, and 2 percent by wind.
    The migration of Oceanic biota was generally from west to east, with four major factors influencing their distribution and establishment. The first was the size and fertility of the islands on which they landed, with larger islands able to provide hospitality for a wider range of species. Second, the further east the islands, generally the less the species diversity, largely because of the distance that had to be crossed and because the eastern islands tended to be smaller, more scattered, and remote. This easterly decline in species diversity is well demonstrated by birds and coral fish. It is estimated that there were over 550 species of birds in New Guinea, 127 in the Solomon Islands, 54 in Fiji, and 17 in the Society Islands. From the west across the Pacific, the Bismarck Archipelago and the Solomon Islands have more than 90 families of shore fish (with many species within the families), Fyi has 50 families, and the Society Islands have 30.Third, the latitude of the islands also influenced the biotic mix, as those islands in relatively cooler latitudes, notably New Zealand, were unsuited to supporting some of the tropical plants with which Pacific islands are generally associated.
    Finally, a fourth major factor in species distribution, and indeed in the shaping of Pacific ecosystems, was wind. It takes little experience on Pacific islands to be aware that there are prevailing winds. To the north of the equator these are called north-easterlies, while to the south they are called south-easterlies. Further south, from about 30° south, the winds are generally from the west. As a result on nearly every island of significant size there is an ecological difference between its windward and leeward (away from the wind) sides. Apart from the wind action itself on plants and soils, wind has a major effect on rain distribution. The Big Island of Hawaii is often cited as a prime example; one can leave Kona on the leeward side in brilliant sunshine and drive across to the windward side where the city of Hilo is blanketed in mist and rain.  [br] In Paragraph 2, what is the author’s purpose in mentioning the estimated numbers of bird species on various Oceanic islands?
选项 A、To give examples of the wide range of species that can be found on Oceanic islands.
B、To demonstrate how much knowledge about Oceanic species has been accumulated.
C、To illustrate the decline in species diversity from west to east on Oceanic islands.
D、To identify the influence of latitude upon Oceanic plants and animals.
答案 C
解析 题目问作者为什么要提到不同大洋洲岛屿上鸟类的数量。第2段第4句提到“鸟类和珊瑚鱼很好地证明了越向东，生物多样性越少这种情况”，接下来的例子是为了验证这句话，故正确答案为C项。A项“为了证明大洋洲岛屿上物种的多样性”、B项“为了证明人类已经积累了大量大洋洲岛屿物种的知识”、D项“解释纬度对大洋洲动植物的影响”均不是作者提到不同大洋洲岛屿上鸟类的数量的原因。
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