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  3. You will now listen to part of a lecture. You will then be asked a question abo

You will now listen to part of a lecture. You will then be asked a question abo

游客2024-01-02  10
问题  You will now listen to part of a lecture. You will then be asked a question about it. After you hear the question, you will have 20 seconds to prepare your response and 60 seconds to speak.
Question: Using points and examples from the talk, explain how the opportunist plant species live and then become extinct in an area.
Opportunist plant species are plants typical of unstable or periodically extreme environments. One characteristic of such plants is the strong ability to spread widely and quickly. Such species are usually smaller than the typical species in an area, and live less long. Thus, initially they can colonize an area rapidly during a favorable period, though in the long term they may lose out to equilibrium species.
Here is a common example of such plant species in the Western U.S. In the upper Great Plains, there is the blue-bunch, a common and dominant plant species in the area. Cattle, however have nearly eliminated the plants. During the period of time when the blue-bunch disappears, another plant species, the leafy spurge has come to predominate the area. However, it only stays for a season like several months, and then the leafy spurge plants will be warded off by the dominant plants. The reason is that if the number of cattle is reduced, due to human activities or climate, to the level that the ordinary state of the environment can re-establish itself, the dominant plant species in the area will come to exist again. Once this is done, over time, the opportunist plant species will disappear.
选项
答案 Opportunist species colonize an area when an environment undergoes a change unfavorable to the dominant plant species. Their dominance is often fast and widespread, but temporary, because opportunist plants can be easily warded off by the original species when the conditions are favorable to the original equilibrium species. For example, in the Great Plain of the Western U.S., the blue-bunch is a common and dominant species in the area, but under the threat of cattle. Once the plants are, by large, consumed by cattle, opportunist species, the leafy spurge comes to predominate the place. But if the cattle are removed or reduced to the degree that the blue-bunch is able to re-establish themselves, the opportunist species will be warded off by the dominant species.
解析     讲座主要讲了机会主义植物是怎样在一个地区达到全胜再走向灭绝的。“Here is a common example of such plant species in the Western U．S．”讲座用美国西部的一种植物来解释这一过程。
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