首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
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
admin
2011-01-08
42
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.
In dozens of years, there are more cases of the invasion of alien species partly because
选项
A、plant seeds are resistant to antibiotics.
B、people tend to hitch a ride.
C、there are more circulation of goods.
D、animal larvae become stronger.
答案
C
解析
细节题。由题干中的关键词alien species定位至第二段。首句明确指出:过去的几十年,随着人和货物的流动日益频繁,植物种子和动物幼体也乘机“搭便车”四处播散,世界各地无意间出现了越来越多的外来物种。可见,货物流动增多是外来物种人侵的原因之一,故[C] 为答案。[A]和[D]未提及,排除。这里搭便车的主体是plant seeds和animal larvae,并非people,[B]属于张冠李戴,排除。
转载请注明原文地址:https://jikaoti.com/ti/7GuYFFFM
0
专业英语八级
相关试题推荐
ItispossibleforstudentstoobtainadvanceddegreesinEnglishwhileknowinglittleornothingabouttraditionalscholarlyme
Forwelloveracentury,onestreetinNewYorkCityhasbeenknownastheheartoftheAmericantheater.Thenameofthestreet
Inthelate1960smanypeopleinNorthAmericaturnedtheirattentiontoenvironmentalproblems,andnewsteel-and-glassskyscra
A、Thisisaninternationalconference.B、Thisisanacademicconference.C、Thisisaformaloccasion.D、Thelanguageusedinthi
Asamatteroffact,whenallalanguagetakesfromanotheroneismerewords,itisusuallybecauseonlyasmallnumberofspea
Asamatteroffact,whenallalanguagetakesfromanotheroneismerewords,itisusuallybecauseonlyasmallnumberofspea
SomerecenthistorianshavearguedthatlifeintheBritishcoloniesinAmericafromapproximately1763to1789wasmarkedbyin
A、Japan’sPrimeMinisterpaysannualvisittoitB、ItisurgingJapanesepoliticianstocontinualvisitsC、ManyAsiancountryst
Yoknapatawphawasaplaceinventedby______inhisnovelsincludingTheSoundandtheFuryandAbsalom,Absalom!
Shelley’smasterpiece,PrometheusUnbound,isaversedrama,whichborrowsthebasicstoryfrom
随机试题
CT2系统采用:FDMlA传输方式,共40个信道,时分双工TDD工作方式。()
论侵犯专利权的法律责任。
秦始皇陵的兵马俑塑造于约
A.苦楝皮B.槟榔C.榧子D.南瓜子能够治吸血虫病的药物是
有关生活热水用水定额确定依据,以下哪条错误?(2004,56)
定额单价法和实物量法是编制施工图预算的两种方法,关于这两种方法的编制步骤和特点,下列说法中正确的是()。
下图在篮球运动中属于()战术。
我国的农历采用天干地支纪年法,天干是:甲、乙、丙、丁、戊、己、庚、辛、壬、癸。地支是:子、丑、寅、卯、辰、巳、午、未、申、酉、戌、亥。以天干地支配年,2015年是乙未年。2020年是()。
语法的递归性
有下面程序代码:PrivateSubCommandl_Click()DimaAsStringa=“COMPUTER”n=search(a,”T”):PrintIIf(n=0,”未找到”,n)End
最新回复
(
0
)