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
"Exotic and Endangered Species" When you hear someone bubbling enthusiastically about an exotic species, you can safely bet t
"Exotic and Endangered Species" When you hear someone bubbling enthusiastically about an exotic species, you can safely bet t
admin
2018-07-24
59
问题
"Exotic and Endangered Species"
When you hear someone bubbling enthusiastically about an exotic species, you can safely bet the speaker isn’t an ecologist. This is a name for a resident of an established community that was deliberately or accidentally moved from its home range and became established elsewhere. Unlike most imports, which can’t take hold outside their home range, an exotic species permanently insinuates itself into a new community.
Sometimes the additions are harmless and even have beneficial effects. More often, they make native species endangered species, which by definition are extremely vulnerable to extinction. Of all species on the rare or endangered lists or that recently became extinct, close to 70 percent owe their precarious existence or demise to displacement by exotic species. Two examples are included here to illustrate the problem.
During the 1800s, British settlers in Australia just couldn’t bond with the koalas and kangaroos, so they started to import familiar animals from their homeland. In 1859, in what would be the start of a wholesale disaster, a northern Australian landowner imported and then released two dozen wild European rabbits (Oryctolagus cuniculus). Good food and good sport hunting—that was the idea. An ideal rabbit habitat with no natural predators was the reality.
Six years later, the landowner had killed 20,000 rabbits and was besieged by 20,000 more. The rabbits displaced livestock, even kangaroos. Now Australia has 200 to 300 million hippityhopping through the southern half of the country. They overgraze perennial grasses in good times and strip bark from shrubs and trees during droughts. You know where they’ve been; they transform grasslands and shrublands into eroded deserts. They have been shot and poisoned. Their warrens have been plowed under, fumigated, and dynamited. Even when all-out assaults reduced their population size by 70 percent, the rapidly reproducing imports made a comeback in less than a year. Did the construction of a 2,000-mile-long fence protect western Australia? No. Rabbits made it to the other side before workers finished the fence.
In 1951, government workers introduced a myxoma virus by way of mildly infected South American rabbits, its normal hosts. This virus causes myxomatosis. The disease has mild effects on South American rabbits that coevolved with the virus but nearly always had lethal effects on O. cuniculus. Biting insects, mainly mosquitoes and fleas, quickly transmit the virus from host to host. Having no coevolved defenses against the novel virus, the European rabbits died in droves. But, as you might expect, natural selection has since favored rapid growth of populations of O. cuniculus resistant to the virus.
In 1991, on an uninhabited island in Spencer Gulf, Australian researchers released a population of rabbits that they had injected with a calcivirus. The rabbits died quickly and relatively painlessly from blood clots in their lungs, hearts, and kidneys. In 1995, the test virus escaped from the island, possibly on insect vectors. It has been killing 80 to 95 percent of the adult rabbits in Australian regions. At this writing, researchers are now questioning whether the calcivirus should be used on a widespread scale, whether it can jump boundaries and infect animals other than rabbits (such as humans), and what the long-term consequences will be.
A vine called kudzu (Pueraria lobata) was deliberately imported from Japan to the United States, where it faces no serious threats from herbivores, pathogens, or competitor plants. In temperate parts of Asia, it is a well-behaved legume with a well-developed root system. It seemed like a good idea to use it to control erosion on hills and highway embankments in the southeastern United States. A With nothing to stop it, though, kudzu’s shoots grew a third of a meter per day. Vines now blanket streambanks, trees, telephone poles, houses, and almost everything else in their path. Attempts to dig up or burn kudzu are futile. Grazing goats and herbicides help, but goats eat other plants, too, and herbicides contaminate water supplies. B Kudzu could reach the Great Lakes by the year 2040.
On the bright side, a Japanese firm is constructing a kudzu farm and processing plant in Alabama. The idea is to export the starch to Asia, where the demand currently exceeds the supply. C Also, kudzu may eventually help reduce logging operations. D At the Georgia Institute of Technology, researchers report that kudzu might become an alternative source for paper.
The word itself in the passage refers to
选项
A、most imports
B、new community
C、home range
D、exotic species
答案
D
解析
"Unlike most imports, which can’t take hold outside their home range, an exotic species permanently insinuates itself [the exotic species] into a new community." The pronoun "itself does not refer to Choices A, B, or C.
转载请注明原文地址:https://kaotiyun.com/show/MRfO777K
0
托福(TOEFL)
相关试题推荐
Labeltheplanbelow.Writethecorrectletter,A-l,nexttoquestions16-20Whereinthemuseumarethefollowingplaces?Sig
Completethesentencesbelow.WriteNOMORETHANTWOWORDSforeachanswer.SavingthejuniperplantBackgroundManyofthebus
Completetheflowchartbelow.ChooseSIXanswersfromtheboxandwritethecorrectletter,A-G,nexttoquestions11-16.Aair
Completethetablebelow.WriteNOMORETHANTWOWORDSAND/ORANUMBERforeachanswer.Talkingaboutthehistoryofbikes
Choosethecorrectletter,A,BorC.Whatistheprimarymethodforincreasingsafety?
Completethenotesbelow.WriteONEWORDONLYforeachanswer.ChimpanzeeBehavioursSpeciesWecanfindPanorPanTroglody
ChooseTHREEletters,A-ETheinventionofdifferentgearsonabicycleaffectedwhichTHREEofthefollowing?AWheelsizeBBa
Whatproblemisidentifiedwitheachofthefollowingnaturaldyes?ChooseSIXanswersfromtheboxandwritethecorrectletter
Choosethecorrectletter,A,BorC.WhyisJilldoubtfulaboutrenewableenergy?
A、Aneducatedpopulation.B、Alargesupplyofgoodsandservices.C、Alargenumberofpublications.D、Anindustrializedsociety.
随机试题
过去我国许多家庭,特别是农村家庭习惯自制米糊、菜汤、蛋黄、肉糜、猪肝、豆制品等作为母乳代用品,随着人民生活水平的提高,如今人们在婴幼儿喂养的过程中越来越关注安全性与营养性,经过精心加工的婴幼儿食品营养更加均衡,食用更安全,满足了消费者的需要。《乳制品质量安
胰岛素受体广泛分布于
企业的资产发生评估增值时,不计入应纳税所得额的有()。
国有企业是商业银行的主要服务对象,也是造成我国国有商业银行资产质量不高、历史包袱沉重的原因之一。现阶段,商业银行对待国有企业的主要应对措施是()。
江苏的嫁娶习俗主要表现在婚姻观念、婚姻形式、婚姻礼仪和离婚制度上,婚姻程序的第一阶段是围绕男女双方家族进行的,有()。
有些幼儿看多了电视上的打打杀杀镜头,很容易增加其以后的攻击性行为。在此,影响幼儿攻击性行为的因素主要是()。
国家通过调节利率高低可以影响经济活动。一般认为,利息增加后带来的经济影响是()。
主观辩证法是()
=_____________
Venturecapitalhasnowbecomeaglobalphenomenon.Hereisthe(1)_____statusofeachmajorregionthathasventurecapitalac
最新回复
(
0
)