2. 考研
  3. Life, at least for a seed, is better out in the world. 【R1】______Seeds know how to get around. 【R2】______But they all have the s

Life, at least for a seed, is better out in the world. 【R1】______Seeds know how to get around. 【R2】______But they all have the s

admin2018-01-31  57
问题    Life, at least for a seed, is better out in the world. 【R1】______Seeds know how to get around. 【R2】______But they all have the same goal: to take root and give rise to the next generation.
   Scientists can understand what type of dispersal strategy a plant employs by looking at its environment. For example, dispersal by sea currents is important for plants that grow on seashores, and wind is important in open grasslands. And for each type of dispersal, there is a type of design. 【R3】______
   "Among species with seeds dispersed internally by animals, the size of the seed or fruit, its color, and the presence of protective husks will reflect the swallowing, visual, and processing abilities of the seed disperser, " Birkinshaw said. For example, seeds spread by small birds will be small in size, covered with plant flesh(to give the birds a reward for eating it), huskless(since most birds are ill equipped to remove such an outer shell), and brightly colored(since birds have good color vision).
   Some seeds have no specific dispersal strategy, like the coco-de-mer, a palm tree that only grows in the Seychelles, an island chain in the Indian Ocean. These palms have the largest seeds of any plant and lack any seed dispersal method other than gravity, Birkinshaw said. In other cases, as with the rare Mada-gascan palms Satranala decussilvae and Voanioala gerardii, the seeds collect in piles beneath their parent trees. 【R4】______
   According to John Dransfield, an expert on Madagascan palms with the United Kingdom’s Royal Botanic Garden, Kew, both of these palms have very large seeds that animals alive today are incapable of moving. "You start dreaming up stories that it could have been distributed by a now extinct animal" , he said.
   Possible extinct dispersers of the palms are large lemurs that once roamed Madagascar or flightless elephant birds, which were the largest birds known to have lived in Madagascar.
   There are only a few of these Madagascan palms left standing. 【R5】______
   Donald Drake is a botanist with the University of Hawaii in Honolulu who studies how plant and animal interaction affects reproduction of native plants and food for native animals in the Pacific Ocean islands. He said loss of animals to disperse seeds certainly impacts a plant’s viability, but "hard, conclusive data are difficult to come by".
   He and colleague Kim McConkey are currently engaged in research that suggests animals may stop performing ecological functions such as seed dispersal long before they go extinct. "We found this to be the case with flying foxes", Drake said. Flying foxes are among the few remaining large animals that disperse seeds on islands in the Pacific and Indian Oceans. "Many flying foxes are either rare or extinct", Drake said, "If they cease to be effective dispersers long before reaching that stage, there is a possibility that the results we found are of wide applicability".
   [A]Wind-dispersed seeds are generally lightweight and have adaptations such as wings and parachutes so they can catch a ride on the breeze. Water-dispersed seeds, such as coconuts, are buoyant. Seeds dispersed by animals usually offer a nutritional reward so that they are eaten, or they are sticky or barbed so they can latch on to passing bodies.
   [B]If researchers can confirm that indeed the animal disperser of the palms, seeds are extinct, then the only way to prevent the trees themselves from becoming extinct may be to reintroduce seedlings into the forest with a controlled program of replanting, Dransfield said.
   [C]In order to maintain effective seed-dispersing populations, the researchers say it is important to take conservation actions before seed-dispersing animal species drop below this threshold.
   [D]Some fly with the wind, others go with the flow. Many hitch a ride with unsuspecting animals.
   [E]Some animals cease being effective seed dispersers when their population densities fall below a point that induces them to compete over food resources—they stop bothering to scatter and hide their food stores.
   [F]In general, seed dispersal away from the parent plant increases the chances that a seed will reach maturity.
   [G]Researchers believe that perhaps their animal dispersers are long extinct.
【R4】
选项
答案G
解析 本段主要讲一些种子没有特定的传播途径，下一段提到有些植物的种子非常大的动物都无法传播它们，并猜想能传播这些种子的动物现在可能巳经灭绝了。因此空白处可能与某些种子的动物传播者灭绝有关，B项、E项、G项都与此有关。但B项说的是如果某些种子的动物传播者真的灭绝了，该如何防止植物物种的灭绝，与下文没有逻辑联系。E项讲的是在什么条件下某些动物传播者不能再有效地传播种子，与题意不符。G项则说研究者认为这些棕榈种子的动物传播者可能很久以前就灭绝了，符合题意，为正确选项。
转载请注明原文地址:https://www.kaotiyun.com/show/8PBZ777K
0

考研英语一

相关试题推荐
随机试题
最新回复(0)