The cane toad is a large (1.8 kg) amphibianspecies native to Central and South America. It was deliberately introduced toAustralia in 1935 with the expectation that it would protect farmers’ crops byeating harmful insects. Unfortunately, the toad multiplied rapidly, and a largecane toad population now threatens small native animals that are not pest.Several measures have been proposed to stop the spread of the cane toad inAustralia.
One way to prevent the spread of the toadwould be to build a national fence. A fence that blocks the advance of thetoads will prevent them from moving into those parts of Australia that they havenot yet colonized. This approach has been used before: a national fence waserected in the early part of the twentieth century to prevent the spread ofrabbits, another animal species that was introduced in Australia from abroadand had a harmful impact on its native ecosystems.
Second, the toads could be captured anddestroyed by volunteers. Cane toads can easily be caught in simple traps andcan even be captured by hand. Young toads and cane toad eggs are even easier togather and destroy, since they are restricted tothe water. If the Australiangovernment were to organize a campaign among Australian citizens to join forcesto destroy the toads, the collective effort might stop the toad from spreading.
Third, researchers are developing adisease-causing virus to control the cane toad populations. This virus will bespecially designed: although it will be able to infect a number of reptile and amphibianspecies, it will not harm most of the infected species; it will specificallyharm only the cane toads. The virus will control the population of cane toadsby preventing them from maturing and reproducing.
- Main point: 提供了三个控制蔗蜍数量的方法
- Sub point 1: 建立全国范围性的围栏
- Sub point 2: 组织志愿者抓
- Sub point 3: 研制某种特殊病毒，阻碍蔗蜍的成熟和繁殖
The cane toad won’t be as easy to get ridof as the reading suggests. The measures proposed by the reading are likelyeither to be unsuccessful or to cause unwanted environmental damage.
First of all, a national fence probablywon’t stop the spread of the toad. That’s because young toads and toad eggs arefound in rivers and streams. No matter where the fence is located, at some pointthere will be rivers or steams flowing from one side to the other. Thesewaterways will be able to carry the young toads and their eggs to the otherside. Since it’s only necessary for a few young toads or eggs to get though thefence in order to establish population on the other side, the fence is unlikelyto be effective.
Secondly, a massive group of volunteers couldhave success trapping and destroying toads. But it’s likely that theseuntrained volunteers would inadvertently destroy many of Australia’s nativefrogs some of which are endangered. It’s not always easy to tell the canetoadapart from native frogs especially when it’s young.
Third, using the virus is a bad ideabecause it could have terrible consequences for cane toads in their originalhabitat in Central and South America. You might be wondering how can virus releasedin Australia cause harm in the Americas. Well, Australian reptiles andamphibians are often transported to other continents by researchers or petcollectors for example. Once the animals infected by the virus reach Centraland South American, the virus will attack the native cane toads and devastatetheir populations. That would be an ecological disaster because in the Americanscane toads are a native species and a vital part of the ecosystem. So if theyare eliminated the whole ecosystem will suffer.
- Main point: 三个方法是无效甚至只有害的
- Sub point 1: 蔗蜍的蝌蚪和卵可以通过流水穿过围栏，方法无效
- Sub point 2: 尽管志愿者可以抓到蔗蜍，但是可能会错抓当地濒危的原产青蛙
- Sub point 3: 使用病毒可能会破坏蔗蜍原产地中南美洲的生态平衡
The lecturer argues against the three measuresmentioned in the reading passage to _____________________.
The lecturer argues that the first measure,_______________________. The reading passage, however, argues that such a______would ______________.
Regarding the second measure,__________, thelecturer explains that ________________. The reading passage gives the oppositeview: ___________________.
Finally, the lecturer objects to the thirdmeasure—_______________. She points out that __________________. This is indirect contradiction with the claim in the reading passage that _____________________.
The lecturer argues against the threemeasures mentioned in the reading passage to reduce the population of the canetoad, a species introduced to the Australian continent.
The lecturer argues that the first measure,a national fence, would not prevent the flow of streams or rivers and,therefore, would allow young toads or toad eggs to travel to the other side ofthe fence. The reading passage, however, argues that such a fence wouldeffectively cut off the route that animals use to establish colonies and expandin population.
Regarding the second measure, recruiting alarge group of volunteers, the lecturer explains that volunteers often havedifficulty distinguishing between cane toads and native frogs, an endangered species;therefore, they might kill members of both species. The reading passage givesthe opposite view: Organizing a large group of volunteers to join anextermination campaign would speed the destruction of cane toads.
Finally, the lecturer objects to the thirdmeasure—using an infectious virus. She points out that a virus intended toeliminate Australia’s cane toad population could be transmitted through animal transportationto other continents where cane toads are an essential part of the ecosystem.This is in direct contradiction with the claim in the reading passage that aninfectious virus could be developed to stop the reproduction of cane toadswithout harming other species.