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
You should spend about 20 minutes on Questions 28 - 39 which are based on Reading Passage 3 below. Popul
You should spend about 20 minutes on Questions 28 - 39 which are based on Reading Passage 3 below. Popul
admin
2013-11-25
100
问题
You should spend about 20 minutes on Questions 28 - 39 which are based on Reading Passage 3 below.
Population viability analysis
Part A
To make political decisions about the extent and type of forestry in a region it is important to understand the consequences of those decisions. One tool for assessing the impact of forestry on the ecosystem is population viability analysis(PVA). This is a tool for predicting the probability that a species will become extinct in a particular region over a specific period. It has been successfully used in the United States to provide input into resource exploitation decisions and assist wildlife managers and there is now enormous potential for using population viability to assist wildlife management in Australia’s forests.
A species becomes extince when the last individual dies. This observation is a useful starting point for any discussion of extinction as it highlights the role of luck and chance in the extinction process. To make a prediction about extinction we need to understand the processes that can contribute to it and these fall into four broad categories which are discussed below.
PartB
A Early attempts to predict population viability were based on demographic uncertainty. Whether an individual survives from one year to the next will largely be a matter of chance. Some pairs may produce several young in a single year while others may produce none in that same year. Small populations will fluctuate enormously because of the random nature of birth and death and these chance fluctuations can cause species extinctions even if, on average, the population size should increase. Taking only this uncertainty of ability to reproduce into account, extinction is unlikely if the number of individuals in a population is above about 50 and the population is growing.
B Small populations cannot avoid a certain amount of inbreeding. This is particularly true if there is a very small number of one sex. For example, if there are only 20 individuals of a species and only one is a male, all future individuals in the species must be descended from that one male. For most animal species such individuals are less likely to survive and reproduce. Inbreeding increases the chance of extinction.
C Variation within a species is the raw material upon which natural selection acts. Without genetic variability a species lacks the capacity to e-volve and cannot adapt to changes in its environment or to new predators and new diseases. The loss of genetic diversity associated with reductions in population size will contribute to the likelihood of extinction.
D Recent research has shown that other factors need to be considered. Australia’s environment fluctuates enormously from year to year. These fluctuations add yet another degree of uncertainty to the survival of many species. Catastrophes such as fire, flood, drought or epidemic may reduce population sizes to a small fraction of their average level. When allowance in made for these two additional elements of uncertainty the population size necessary to be confident of persistence for a few hundred years may increase to several thousand.
Part C
Beside these processes we need to bear in mind the distribution of a population. A species that occurs in five isolated places each containing 20 individuals will not have the same probability of extinction as a species with a single population of 100 individuals in a single locality.
Where logging occurs(that is, the cutting down of forests for timber)forest-dependent creatures in that area will be forced to leave. Ground-dwelling herbivores may return within a decade. However, arboreal marsupials(that is animals which live in trees)may not recover to pre-logging densities for over a century. As more forests are logged, animal population sizes will be reduced further. Regardless of the theory or model that we choose, a reduction in population size decreases the genetic diversity of a population and increases the probability of extinction because of any or all of the processes listed above, It is therefore a scientific fact that increasing the area that is logged in any region will increase the probability that forest-dependent animals will become extinct.
Do the following statements agree with the views of the writer in Part A of Reading Passage 31 In
boxes 28 - 31 on your answer sheet write
YES if the statement agrees with the writer
NO if the statement contradicts the writer
NOT GIVEN if it is impossible to say what the writer thinks about this
Example Answer
A link exists between the consequences of decisions and the decision making process itself. YES
PVA has been used in Australia for many years.
选项
A、YES
B、NO
C、NOT GIVEN
答案
B
解析
转载请注明原文地址:https://kaotiyun.com/show/F1NO777K
本试题收录于:
雅思阅读题库雅思(IELTS)分类
0
雅思阅读
雅思(IELTS)
相关试题推荐
EachofQuestions1to7presentstwoquantities.QuantityAandQuantityB.Comparethetwoquantities.Youmayuseadditional
Whichofthefollowingstatementsaretrue?(a)-5
Findanalgebraicexpressiontorepresenteachofthefollowing.(a)Thesquareofyissubtractedfrom5,andtheresultismult
Solveeachofthefollowingsystemsofequationsforxandy.(a)x+y=24x-y=l8(b)3x-y=-5x+2y=3(c)15x-18-2y=-3
ForeachofQuestions1to9,compareQuantityAandQuantityB,usingadditionalinformationcenteredabovethetwoquantities
ForeachofQuestions1to9,compareQuantityAandQuantityB,usingadditionalinformationcenteredabovethetwoquantities
Ofthepeopleinacertainsurvey,58percentwereatmost40yearsoldand70percentwereatmost60yearsold.If252ofthe
Approximatelywhatwasthepercentincreaseintheannualrevenuefromallgreetingcardsalesfrom1990to1993?
Acircularwheeltravelsalongaflatsurfaceataconstantrateof2.5feetpersecond.Howmanycompleterevolutionswillthe
Afterpeoplebegantomakethetransitionfromgatheringfoodtoproducingfood,humansocietiesfollowedmarkedly______courses;
随机试题
A.感音神经性聋B.传导性聋C.混合性聋D.噪声性聋E.伪聋分泌性中耳炎导致的听力损失一般为
大脑中动脉脑梗死的主要表现是
公路工程质量事故分为()。
孙玉和丈夫廖先生都是公司的高层管理者,两人处于职业生涯的重要时期,工作繁忙,无法花很多时间在投资理财上,于是向理财规划师咨询,希望能够帮助他们制定理财规划。理财规划师通过交谈获得相关信息如下:一、家庭成员表五、客户的特殊状况与理财目标1.短期目标:
在一元线性回归的总偏差平方和的表达式中,结论正确的是()。
岩溶地貌又称喀斯特,因欧洲亚得里亚海岸的喀斯特高原而得名。()
“黄泽不竭;老子其犹”中的下半句的原句是()。
简述配送中心规划与设计的原则。
_______是指在教练员指导下或实施运动员自我计划的前提下,为全面提高运动员竞技能力和专项运动成绩而专门组织进行的教育活动或过程。
下列犯罪中没有现实的损害后果也可以构成既遂的是()。
最新回复
(
0
)