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 be
"Exotic and Endangered Species" → When you hear someone bubbling enthusiastically about an exotic species, you can safely be
admin
2012-01-14
42
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://www.kaotiyun.com/show/rNyO777K
0
托福(TOEFL)
相关试题推荐
Atthestartofthetutorial,thetutoremphasisestheimportanceofAnexampleofapersonwhodoesn’t’fitin’issomeonewho
Completethenotesbelow.WriteONEWORDONLYforeachanswer.TheTawnyOwlMost【L31】______owlspeciesinUKStronglynocturna
Completethenotesbelow.WriteONEWORDONLYforeachanswer.TheTawnyOwlMost【L31】______owlspeciesinUKStronglynocturna
Completethenotesbelow.WriteONEWORDONLYforeachanswer.TheTawnyOwlMost【L31】______owlspeciesinUKStronglynocturna
Completethenotesbelow.WriteONEWORDONLYforeachanswer.TheTawnyOwlMost【L31】______owlspeciesinUKStronglynocturna
Completethenotesbelow.WriteONEWORDONLYforeachanswer.ChimpanzeeBehavioursSpeciesWecanfindPanorPanTroglody
Completethenotesbelow.WriteONEWORDONLYforeachanswer.ChimpanzeeBehavioursSpeciesWecanfindPanorPanTroglody
Completethenotesbelow.WriteONEWORDONLYforeachanswer.ChimpanzeeBehavioursSpeciesWecanfindPanorPanTroglody
Completethenotesbelow.WriteONEWORDONLYforeachanswer.ChimpanzeeBehavioursSpeciesWecanfindPanorPanTroglody
随机试题
中年或中年以上患者,近期出现排便习惯改变或血便,最有意义的检查是
工程保修阶段监理单位的工作有()。
影响混凝土强度的主要因素包括()。
海关发现进出口货物报关单需要进行修改或者撤销的,收发货人或其代理人应当提交进出口货物报关单修改/撤销申请表。
在我国构成违约责任必须同时具备的条件有()。
在古罗马帝国,当古罗马人不再是至高无上的族群,帝国的控制权转移到了由多民族精英组成的群体,伊利里亚人、高卢人和迦太基人继续传承和发扬着古罗马文化;在伊斯兰帝国,当阿拉伯人失去对伊斯兰世界的控制权,埃及人、伊朗人和柏柏尔人继续发扬着穆斯林文化;对欧洲帝国主义
下面哪条语句在编译时不会出现错误或警告()。
下列代码的执行结果是()。publicclassTest3{publicstaticvoidmain(Stringargs[]){System.out.pnntln(100%3);Sy
A.他为什么这么难过?B.这种裙子有红色和蓝色的,您要哪一条?C.祝你生日快乐!D.你想去打篮球还是想在家上网?E.你在中国的时候经常给家里写信吗?F.喂,是机场办公室吗?谢谢你的礼物,我太高兴了。()
SouthernNewspaperGroup-titlesincludetheDailyRecord
最新回复
(
0
)