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  3. The Extinction of Moa (1

The Extinction of Moa (1

游客2024-01-02  5
问题                                                     The Extinction of Moa
    (1) Between 80 and 85 million years ago, Gondwanaland, a giant continent made up of what today is Africa, Antarctica, Australia, and South America, broke up, thus causing what is now New Zealand to become separated from the larger landmass. After the separation, any creature unable to cross a considerable distance of ocean could not migrate to New Zealand. Snakes and most mammals evolved after the separation. Thus there are no New Zealand snakes, and bats, which flew there, and seals, which swam there, were the only mammals on New Zealand when Polynesian settlers (the Maori) arrived there about a thousand years ago.
    (2) [A]When the Maori arrived in New Zealand, they encountered birds that had been evolving for 80 million years without the presence of mammalian predators. The most striking of these animals must have been moa. Now extinct, moa were gigantic wingless birds that stood as much as 10 feet (3 meters) tall and weighed as much as 550 pounds (250 kilograms). They are known from a diverse array of remains including eggshells, eggs, a few mummified carcasses, vast numbers of bones, and some older fossilized bones. [A]The species of moa that are currently recognized occupied ecological niches customarily filled elsewhere by large mammalian browsing herbivores. [D]They may have had relatively low reproductive rates; apparently, they usually laid only one egg at a time.
    (3) It seems possible that when Captain James Cook first visited New Zealand in 1769, moa (or at least one of the moa species) may have still survived in the remote areas in the western part of New Zealand’s South Island. If so, these individuals would have been the last of their kind. Climatic conditions in New Zealand appear to have been relatively stable over the period during which moa became extinct. Different factors could have worked in concert to account for their abrupt disappearance.
    (4) [E]Vegetation was considerably altered by the Maori occupation of New Zealand, a change not easily explained by climate variation or other possible factors. Forest and shrubland burning appears to have reduced the prime habitat of many moa species. [C]However, the main forest burning started around 700 years ago, after what current archeological evidence indicates was the most intensive stage of moa hunting. While there appears to have been extensive burning on the east side of New Zealand’s South Island, large forest tracts remained in the most southern part of the island. [G]Because major habitat destruction seems to have occurred after moa populations already were depleted, and because some habitats that could have sheltered moa populations remained, it would seem that other factors were also at work in the extinction of these birds.
    (5) [E]For South Island, human predation appears to have been a significant factor in the depletion of the population of moa. At one excavated Maori site, moa remains filled six railway cars. The density of Maori settlements and artifacts increased substantially at the time of the most intensive moa hunting (900 to 600 years ago). This period was followed by a time of decline in the Maori population and a societal transition to smaller, less numerous settlements. The apparent decline fits the pattern expected as a consequence of the Maori’s overexploitation of moa.
    (6) [F]Finally, the Maori introduced the Polynesian rat and the dog to New Zealand. The actions of these potential nest predators could have reduced moa populations without leaving much direct evidence. The Maori may have also inadvertently brought pests and disease organisms in fowls, which could have crossed over to eradicate moa populations. [B]The possibility of analyzing ancient DNA to identify past diseases of extinct animals is being explored. However, evidence of such diseases is difficult to determine directly from paleoecological or archeological remains. For these reasons, it is hard to determine the likelihood that introduced disease organisms were a cause of the decline of moa, but they are potentially significant.
    (7) While the last of these possible causes remains speculative, define clues exist for the action of the first two causes. The story of moa species and their demise raises ecological issues on the vulnerability of species to human-caused changes—including altered vegetative cover of the landscape, change in the physical environment, and modification of the flora and fauna of a region by eliminating some species and introducing others.
    An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage.  This question is worth 2 points.
Moa were large, flightless birds of New Zealand that became extinct several centuries ago.
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    Answer Choices
    (A)  Because New Zealand had no large mammals, moa had no mammalian predators and occupied the ecological niches that elsewhere were occupied by large mammalian herbivores.
    (B)  DNA analysis of moa remains revealed that the extinction of moa species occurred less than three centuries ago.
    (C)  Scientists claim that forest burning is the factor most responsible for the disappearance of moa.
    (D)  Initially, moa had a high reproductive rate, but overtime it significantly declined, largely due to changes in New Zealand’s climatic pattern.
    (E)  The extinction of moa was primarily caused by the hunting and deforestation activities of the Maori, who arrived in New Zealand about one thousand years ago.
    (F)  The Maori introduced dogs, rats, and perhaps disease organisms, which may have contributed to the extinction of moa, but evidence is not available.
选项
答案 A,E,F
解析 首先看选项的内容。A项“由于新西兰没有大型哺乳动物，因此，恐鸟没有哺乳类捕食者，还占据了其他地方被大型哺乳类食草动物占据的生态位”，根据关键词mammalian predators可定位到第2段。该项对应第2段的第1句和倒数第2句，选项内容没有与原文不符的情况，因此，可先保留。B项意为“对恐鸟遗骸的DNA分析显示，恐鸟物种的灭绝发生在不到三个世纪前。”根据本项的关键词DNA，可定位到全文唯一出现过DNA的第6段第4句，明显B项的内容与此处原文没有任何相关性，为毫无根据的选项。C项“科学家们称燃烧森林是导致恐鸟消失的最主要因素”，根据关键词forest burning可定位到第4段，从第3句及之后的内容可知，燃烧森林并非恐鸟消失的主要原因，再者，原文也没有确切说法能证明此项。D项“最初，恐鸟的繁殖率很高，但随着时间的推移，它们的繁殖率明显下降了，这主要是由新西兰气候模式的变化造成的”，根据选项关键词reproductive rate可定位到第2段最后一句，该句提到恐鸟繁殖率低，并没有提到其有繁殖率高的情况，故该项错误。做题至此，我们已经把与原文内容不符的三个项都排除了，所以暂时这道题选A、E、F三项。然后为了确认其正确性。可以把剩下的两个项也看完。E项“恐鸟的灭绝主要是由1,000年前到达新西兰的毛利人的狩猎和森林砍伐活动造成的”，狩猎和森林砍伐分别对应了第5段和第4段，均为恐鸟灭绝的原因之一。F项“毛利人引进了狗、老鼠，也许还有携带病菌的生物，这可能是导致恐鸟灭绝的原因，但是没有证据”，对应第6段的内容，也是本文的观点之一，故本题确定选A、E、F三项。
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