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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2023-12-25  34
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] According to Paragraph 2, all of the following types of islands are associated with higher species diversity EXCEPT________.
选项 A、islands that are large in size
B、islands located in cool latitudes
C、islands located in the western part of Oceania
D、islands located near other landmasses
答案 B
解析 题目问哪种类型的岛屿生物多样性较少。根据第2段最后一句可推测，纬度越高的岛屿，温度较低，越不适合某些动植物的生长，其生物多样性也会相对而言更少，因此B项符合题意，是正确答案。第2段第2句提到越大型的岛屿越能容纳更多的物种，因此生物多样性也更多，故A项不符合题意，可排除。根据第2段第3句“岛屿越偏东，生物多样性越少，主要是考虑到迁徙距离，而且因为东部岛屿往往更小、更分散、更偏远”，可推测偏西的岛屿以及不偏远、不分散、与其他陆地相距较近的岛屿的物种都比较丰富，C项“海洋西部的岛屿”以及D项“靠近其他陆地的岛屿”不符合题意，故均予以排除。
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