机经真题 9 Passage 1

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Engines of Diversity

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According to paragraph 3, how do ants promote plant diversity?

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  • A
    By bringing seeds from different places into their nests
  • B
    By creating favorable sprouting conditions for seeds in different locations in their colonies
  • C
    By preventing seeds from being eaten and keeping them within a limited area
  • D
    By bringing together seeds of otherwise isolated plants into a location where the plants can reproduce with one another
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正确答案: C

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  • A species does not just adapt to its physical environment but also to its biological environment-the species with which it shares intimate ecological relationships. What makes the biological environment different from the physical environment is that it can also evolve. As a species adapts to its ecological partners, its partners can adapt to it as well. Biologists refer to this reciprocal evolutionary change in interacting species as coevolution.



    Coevolution can help drive some populations to evolve into distinct species. One of the few tree species to survive in the Mojave Desert, the Joshua tree (Yucca brevifolia), is pollinated by a species of yucca moth called Tegeticula synthetica in the western part of its range; in the east, it is pollinated by another species called Tegeticula antithetica. Biologist Olle Pellmyr and his colleagues have reconstructed the evolution of the tree and the moths on which it depends to carry its pollen to other trees for fertilization. They found that the ancestor of both moth species was already pollinating Joshua trees. Only later did the two species divide, each specializing on one population of the trees. In response, the scientists have found, Joshua trees have evolved canals in their flowers to match the length of the tongues of their own species of yucca moth. If the trees and moths continue to diverge, there will be less and less opportunity for pollen to move from one population of Joshua trees to another. Ultimately this could lead to the development of different species.



    Over millions of years, this kind of coevolution can have a profound impact on biodiversity. Biologist Szabolcs Lengyel and his colleagues recently took a look at the diversity that arises from the coevolution of flowering plants and the ants that spread their seeds. About 11,000 known plant species around the world grow fleshy handles on their seeds called elaiosomes that serve as food for the ants. After ants bring the seeds to their nests and eat the elaiosomes, they discard the seeds in a special room in their colony. There the seeds can sprout, protected from being eaten by other animals. Elaiosomes have evolved independently at least 101 times, as Lengyel and his colleagues reported in 2009. They also found that the ant lineages that disperse plant seeds contain over twice as many species as the most closely related lineages of plants. Ants may foster plant diversity by protecting seeds and by keeping them growing in a small range around their colonies, causing them to become isolated and therefore unable to reproduce with plants in other locations.



    The world's biodiversity is now experiencing mass extinctions on a scale rarely seen in the history of life. Some scientists are trying to understand how coevolution will affect which species survive and which disappear. If one species depends on another one for its survival, then it will not be able to endure after the other species becomes extinct. If it can shift to a new partner, however, it may be able to survive. Mass extinctions in the past offer some clues to how coevolution makes species vulnerable. Some species of corals live mutualistically with algae-that is, the two species exist in a relationship that benefits each-while some do not. In the last major mass extinctions, 66 million years ago, the mutualist corals suffered about four times more extinctions than the nonmutualists. The mass extinctions coincided with a huge asteroid impact that blocked out the light of the Sun for months. It is possible that this blackout killed off algae as well as the corals that depended on them for survival.



    Today we can see a growing number of species that have lost their coevolutionary partners. In Central America and South America, a number of trees grow giant fruits with massive seeds at their core. Biologist Daniel Janzen has argued that these giant fruits are the result of coevolution with giant mammals, such as ground sloths. The mammals ate the fruits and spread the seeds in their droppings. Around 12,000 years ago, giant sloths and other big mammals disappeared, probably hunted by newly arrived humans. The trees survived, still producing their giant fruits. They can be dispersed today by cows and rats, but not as successfully as they were in the past.


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    【题型】事实信息题

    【答案】C

    【解析】

    A. 错误。原文并未提到蚂蚁从不同地方带来种子,而是描述了蚂蚁将种子带回巢穴并丢弃在特别的地方。

    B. 错误。虽然原文提到蚂蚁将种子置于保护区,避免其他动物吃掉,这确实创造了有利于发芽的条件。然而,关键在于保持种子在巢穴周围,导致其无法与其它地方的植物繁殖,而这也是推动植物多样性的重要因素,这个选项并未完整提及。

    C.正确。原文说明了蚂蚁保护种子,防止其被吃掉,并让种子在巢穴周围的有限区域内成长,从而导致植物隔离,无法与其他地方的植物繁殖,这正是促进植物多样性的原因。

    D. 错误。原文并未提到蚂蚁将隔离的植物种子聚集到一个地方进行繁殖,而相反是保持种子在有限的区域内成长,导致隔离,增加了植物多样性。

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