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  3. Plant and Animal Life of the Pacific Islands P1: The Pacific Islands region covers 32 million square kilometers and is one of th

Plant and Animal Life of the Pacific Islands P1: The Pacific Islands region covers 32 million square kilometers and is one of th

admin2018-10-18  100
问题 Plant and Animal Life of the Pacific Islands
P1: The Pacific Islands region covers 32 million square kilometers and is one of the richest, most complex terrestrial and marine ecosystems on Earth. Some islands that used to be parts of continents still carry some small plant and animal remnants of their earlier biota, providing clear examples of evolution and interesting patterns of colonization, adaptation, and speciation. Cn the contrary, some other islands arose due to volcanic activity or reef growth, which usually subside over time due to erosion and changing sea levels. When islands emerge, they undergo the process of ecological succession as species colonize the island. 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 due to being transported by birds, 23 percent by floating, and 2 percent by wind.
P2: Four major factors account for the fact that the plants and animals on Oceanic islands largely migrate from west to east. The size and fertility of the territory of certain islands is the first determining factor. That is, the larger the islands are, the wider the range of species they are able to support. Second, the further east the islands are, generally the less the diversity of species found there, largely because the eastern islands tended to be smaller, more scattered, and remote, as evidenced by the easterly decline in species diversity of 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 , Fiji 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.
P3: The fourth factor that has influenced species distribution and the shaping of Pacific ecosystems was wind. There are strong prevailing winds throughout the Pacific Ocean, which has been known for centuries due to scientific development. Those in the northern hemisphere are called "North-easterlies", while their counterparts of the southern hemisphere are known as "south-easterlies." Further south, beginning from approximately thirty degrees south, the winds are mostly from the west. Therefore, on nearly every single island of large scale exists an ecological difference between its windward and leeward sides. Apart from the wind action itself on plants and soils, wind has a major effect on rain distribution. The Big Island of Hawaii offers 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.
P4: The long geological isolation of the Pacific islands and their particular climatic conditions have combined to create a unique and spectacular ecosystem. New species cannot immigrate via land, and instead must arrive via air, water, or wind. As a result, organisms with high dispersal capabilities, such as plants and birds, are much more common on islands than are poorly dispersing taxa like mammals. Since immigration of predators and competitors is limited, many species of flightless and ground-nesting birds are able to persist in these new niches. This results in a high occurrence of endemism, where species are unique to a localized area. Besides, endemism is often the result of adaptive radiation, when a single species colonizes an area and rapidly diversifies to fill all of the available niches. These endemic species derived form adaptive radiation are often small in number, unused to serious predation, limited in range, and therefore vulnerable to disruption.
P1: The Pacific Islands region covers 32 million square kilometers and is one of the richest, most complex terrestrial and marine ecosystems on Earth. ■ Some islands that used to be parts of continents still carry some small plant and animal remnants of their earlier biota, providing clear examples of evolution and interesting patterns of colonization, adaptation, and speciation. ■ On the contrary, some other islands arose due to volcanic activity or reef growth, which usually subside over time due to erosion and changing sea levels. ■ When islands emerge, they undergo the process of ecological succession as species colonize the island. ■ 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 due to being transported by birds, 23 percent by floating, and 2 percent by wind.
In paragraph 2, what is the author’s purpose in mentioning the estimated numbers of birds and coral fish 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 【修辞目的题】文中提到越往东的海岛物种多样性越少，比如，鸟类和珊瑚鱼的物种多样性就是越往东越少。所以作者后面提到的鸟类和珊瑚鱼的估测数量是为了说明大洋洲岛屿的物种多样性是从西到东减少的。
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