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
69
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.
Look at the four squares [■] that show where the following sentence could be inserted in the passage.
Asians use a starch extract from kudzu in drinks, herbal medicines, and candy.
Where could the sentence best be added?
Click on a square [■] to insert the sentence in the passage.
选项
A、
B、
C、
D、
答案
C
解析
Vocabulary reference is a transitional device that connects the insert sentence with the previous sentence. The connection is the reference to "starch" in both the insert sentence and the previous sentence.
转载请注明原文地址:https://kaotiyun.com/show/NRfO777K
0
托福(TOEFL)
相关试题推荐
Completethenotesbelow.WriteONEWORDONLYforeachanswer.TheTawnyOwlMost【L31】______owlspeciesinUKStronglynocturna
Completethenotesbelow.WriteONEWORDONLYforeachanswer.TheTawnyOwlMost【L31】______owlspeciesinUKStronglynocturna
Completethenotesbelow.WriteONEWORDONLYforeachanswer.TheTawnyOwlMost【L31】______owlspeciesinUKStronglynocturna
Choosethecorrectletter,A,BorC.WhatdoesJimthinkaboutthedifferenceamongspeciesinnaturalandartificiallight?
Completethenotesbelow.WriteONEWORDONLYforeachanswer.ChimpanzeeBehavioursSpeciesWecanfindPanorPanTroglody
Choosethecorrectletter,A,BorC.WhatdoesJimthinkaboutthedifferenceamongspeciesinnaturalandartificiallight?
随机试题
导游小姚正在制作一份介绍首都北京的演示文稿,按照下列要求帮助她组织材料完成演示文稿的整合制作,完成后的演示文稿共包含19张幻灯片,其中不能出现空白幻灯片。在第1张幻灯片中插入音乐文件“北京欢迎你.mp3”,当放映演示文稿时自动隐藏该音频图标,单击该幻灯
确定的,肯定的adj.a__________
新时代中国特色社会主义基本方略中坚持党对一切工作的领导,就是要()
下列能引起外周阻力降低的是
案例2009年8月21日21时30分,K公司炼铁厂发生煤气中毒较大事故。造成6人死亡,1人受伤,直接经济损失500余万元。2009年8月21日19时25分,炼铁厂1号高炉主风机跳闸断电,高炉被迫休风。19时45分左右,故障排除,热风班开
大跨径劲性骨架混凝土拱桥拱圈浇筑前应进行()。
某企业资产总额年末数为1163150元,流动负债年末数为168150元,长期负债年末数为205000元,则该企业年末的资产负债率为(D)。
()是旅游团抵达后的一项重要工作,前者面向绝大多数旅游团队和散客旅游者,后者只针对特种旅游团队、重点旅游团队或散客。
艺术地记录与再现中华文明的璀璨和辉煌,不仅是对外传播的有效_________,也是在青少年中传承历史,让民族优秀文化传统_________的重要举措。填入划横线部分最恰当的一项是()。
Whetherwewantitornotweareallgreedybynature.Fromthemomentweare【C1】______andtothelastdayofourlifewe【C2】___
最新回复
(
0
)