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  3. What makes for a successful invasion? Often, the answer is to have better weapons than the enemy. And, as it is with people, so

What makes for a successful invasion? Often, the answer is to have better weapons than the enemy. And, as it is with people, so

admin2011-01-08  58
问题     What makes for a successful invasion? Often, the answer is to have better weapons than the enemy. And, as it is with people, so it is with plants—at least, that is the conclusion of a paper published in Biology Letters by Naomi Cappueeino, of Carleton University, and Thor Arnason, of the University of Ottawa, both in Canada.
    The phenomenon of alien species popping up unexpected parts of the world has grown over the past few decades as people and goods become more mobile and plant seeds and animal larvae have hitched along for the ride. Most such aliens blend into the ecosystem in which they arrive without too much fuss. (Indeed, many probably fail to establish themselves at all—but those failures, of course, are never noticed.) Occasionally, though, something goes bananas and starts ttarts to take the place over, and an invasive species is born. Dr. Cappuceino and Dr. Arnason asked themselves why.
    One hypothesis is that aliens leave their predators behind. Since the predators in their new homelands are not adapted to exploit them, they are able to reproduce unchecked. That is a nice idea, but it does not explain why only certain aliens become invasive. Dr. Cappuccino and Dr. Amason suspected this might be because native predators are sometimes "pre-adapted" to the aliens’ defenees, but in other cases they are not.
    To test this, they had first to establish a reliable list of invaders. That is not as easy as it sounds. As they observe, "although there are many lists of invasive species published by governmental agencies, inclusion of a given species in the lists may not be entirely hee of political motivation". Instead, they polled established researchers in the field of alien species, aski,g each to list ten invasive species and, for comparison, ten aliens that just rubbed along quietly with their neighbours. The result was a list of 21 species widely agreed to be invasive and, for comparison, 18 non-invasive aliens.
    Having established these lists, they went to the library to find out what was known about the plants’ chemistry. Their aim was to find the most prominent chemical weapon in each plant, whether that weapon was directed against insects that might want to eat the plant, bacteria and fungi that might want to infect it, or other plants that might compete for space, water, nutrients and light. Botanists know a lot about which sorts of compounds have what roles, so classifying constituent chemicals in this way was not too hard.
    The researchers then compared the chemical arsenals of their aliens with those of native North American plants, to see if superior (or, at least, unusual) weapomT was the explanation for the invaders’ success. Their hypothesis was that highly invasive species would have chemical weapons not found in native plants, and which pests, parasites and other plants would therefore not have evolved any resistance to. The more benign aliens, by contrast, were predicted to have arsenals also found in at least some native species.
    And so it proved. More than 40% of the invasive species had a chemical unknown to native plants; just over 10% of the non-invasive aliens had such a chemical. Moreover, when they looked at past studies on alien plants that had examined how much such plants suffer from the depredations of herbivorous insects, they found that the extent of the damage reported was significantly conelated with the number of native species with which that alien shared its principal chemical weapon.
    For alien plants, then, the real secret of success—also as in human warfare—is surprise. It is not that the chemicals concerned are more toxic in any general sense (indeed, successful invaders are often rare in their own native habitats). Rather, it is that the locals just don’t see them coming.
The difference between Dr. Cappuccino and Dr. Arnason’s hypothesis and the previous one is that
选项 A、the former mentions native predators of alien species.
B、the former may account for the invasion of certain aliens.
C、the latter explains the adaptation of the predators.
D、the latter may explore the pre-adaptation of the predators.
答案B
解析 推断题。由题干中的hypothesis定位至第三段。前两句对其他人的假设进行了解释：有人推 想，外来物种摆脱了原先的掠食者，而在新的“家园”，现有的掠食者又没有发现它们也合口 味，因此这些物种得以肆无忌惮地繁衍。然后指出这一观点的问题：这种观点好是好，不过 没有解释为什么只有特定的外来物种才具有入侵性。该段末句指出Dr. Cappuccino和Dr. Arnason的猜测：这可能是因为土生土长的掠食者对外来物种所具有的防御机制有时产生 “预适应”，有时又不产生。显然，先前假设存在的问题就是这两个人研究的内容，故[B]为 答案。从该段可知，两种假设都提及predators，排除[A]。提到pre-adapted的是Dr. Cappuccino 和Dr. Arnason，[D]属于张冠李戴，排除；而[C]则为该先前假设的部分内容，但无法得 知是否为两种假设的区别所在，排除。  
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