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
84
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.
According to paragraph 6, the Spencer Gulf experiment was dangerous because
选项
A、insect populations were exposed to a virus
B、rabbits on the island died from a virus
C、the virus may be a threat to humans
D、some animals are immune to the virus
答案
C
解析
"... researchers are now questioning whether... it can . . . infect animals other than rabbits (such as humans)." Choice A is not correct because insects were not mentioned in the Spencer Gulf experiment. Choice B is not correct because the purpose of the experiment was to kill the rabbits. Choice D is not correct because 80 to 95 percent of the rabbits are being killed, but the small number with immunity is not identified as dangerous.
转载请注明原文地址:https://kaotiyun.com/show/5RfO777K
0
托福(TOEFL)
相关试题推荐
Completethenotesbelow.WriteONEWORDONLYforeachanswer.TheTawnyOwlMost【L31】______owlspeciesinUKStronglynocturna
Completethenotesbelow.WriteONEWORDONLYforeachanswer.TheTawnyOwlMost【L31】______owlspeciesinUKStronglynocturna
Completethesentencesbelow.WriteNOMORETHANTWOWORDSforeachanswer.SavingthejuniperplantBackgroundItssmokeisvi
WhatdidPhoebefinddifficultaboutthedifferentresearchtechniquessheused?ChooseFIVEanswersfromtheboxandwritethe
WhatdidPhoebefinddifficultaboutthedifferentresearchtechniquessheused?ChooseFIVEanswersfromtheboxandwritethe
ChooseTHREEletters,A-ETheinventionofdifferentgearsonabicycleaffectedwhichTHREEofthefollowing?AWheelsizeBBa
Completethesentencesbelow.WriteONLYONEWORDforeachanswer.ManufacturingintheEnglishMidlandsIn
Choosethecorrectletter,A,BorC.WhatdifficultydoesJillhavewiththeenergymeters?
ResearchingtheoriginofmedievalmanuscriptsBackgroundMedievalmanuscripts—handwrittenbooksproducedbetweenthefifth
CreatingartificialgillsBackgroundTakinginoxygen;mammals—lungs;fish—gillsLong-helddreams—humansswimming
随机试题
国际私法中反致和转致的结果()
将儒家的“三纲”法典化的是
Foodisfuel.Youneeditforenergy.Whenyoudon’teat,youloseenergy.It’sthatsimple.【R1】______Unfortunately,itisalmost
突水部位发潮、滴水且滴水现象逐渐增大,仔细观察发现水中含有少量细砂属于矿井突水预兆中的()。
资产负债表的“年初数”栏内各项数字,一般应根据上年末资产负债表的“期末数”栏内所列数字填列。()
关于结算担保金,下列表述正确的是()。[2015年5月真题]
据现有资料,最早把编辑学作为一门独立学科进行研究的国家是()。
(1997年试题,二)设则三条直线交于一点的充要条件是().
窗体上已有1个名称为Picturel的图片框,要求实现下面2个功能之一:(1)在窗体上移动鼠标时,立即将Picturel显示在鼠标位置(2)在窗体上单击鼠标时,立即将Picturel显示在鼠标位置下面不能实现上述任何功能的事件过程是
A、Sheisarrogant.B、Sheisinexperienced.C、SheisconfidentD、Sheisoffensive.C①四个选项都是形容女士的某个特征,在听录音时要特别留意对话双方的语气。②从女士的介绍话语I
最新回复
(
0
)