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
Population Viability Analysis Part A To make political decisions about the extent and type of forestry in a region it is imp
Population Viability Analysis Part A To make political decisions about the extent and type of forestry in a region it is imp
admin
2010-08-04
22
问题
Population Viability Analysis
Part A
To make political decisions about the extent and type of forestry in a region it is important to understand tile 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 extinct when the last individuals 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 princesses that can contribute to it and these fail into four broad categories which are discussed below.
Part B
A
Early attempts to predict population viability, were based on demographic uncertainty whether an individual survives from one year to time next will largely be 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 leas 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 evolve 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 is 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 individual 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) forests 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 increase 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.
Scientists are interested in the effect of forestry on native animals.
选项
A、Y
B、N
C、NG
答案
A
解析
转载请注明原文地址:https://jikaoti.com/ti/mftFFFFM
0
大学英语四级
相关试题推荐
HowtoDealwithDifficultPeopleInNewYorkoneday,abusinesswomangotintoataxi.Becauseitwasrushhourandshewas
DoctorsataDutchhospital【S1】______anewkindofsurgeryonFridaytocorrectheartburn(胃痛)withoutmakinganyexternalincisi
A、YoungVirginiangentlemenusuallywenttotheCollegeofWilliamandMaryinWashington’stime.B、JohnAdamswasverywell-edu
Moods,saytheexperts,areemotionsthattendtobecomefixed,influencingone’soutlookforhours,daysorevenweeks.That’s
Moods,saytheexperts,areemotionsthattendtobecomefixed,influencingone’soutlookforhours,daysorevenweeks.That’s
Whotalksmore,womenormen?Theseemingly【S1】______evidenceisreconciledbythedifferencebetweenwhatIcallpublicandpri
A、Tochooseamountain.B、Todecideonamountain.C、Tofindthehighestmountain.D、Toclimbthehighestmountain.D信息词next指下一座
A、Leisuresportingactivities.B、Averageageofathletes.C、Durabilityofsportingequipment.D、Friday’sbusinessmeeting.A女士的第
OriginsofMoneyandofBankingWhatIsMoney?Itisalmostimpossibletodefinemoneyintermsofitsphysicalformor
A、Exercisingtheentirebody.B、Havingyourbloodpressuretakendaily.C、Losingweightpriortoexercising.D、Weighinginbefor
随机试题
我国古代园林的成熟阶段是()。
某企业生产两种产品的产量和单位成本资料如下:要求(1)计算该企业总成本指数及总成本的增长量;(2)计算该企业产量总指数及产量变动对总成本变动的绝对影响;(3)计算该企业单位成本总指数及单位成本变动对总成本变动的绝对影响;(4)从相对数和绝对数两方
买方的代理人和卖方商定抬高价金,由后者付给前者一定比例的回扣,这属于()行为。
某企业通过土地出让方式取得土地使用权,下列说法不正确的是:()
地基验槽时,应重点观察()。
下列情形不是企业出现的早期财务预警信号的是()。
某研究所的研究员王某利用本单位的物质技术条件完成了一项发明,之前王某与研究所就该项发明有一份协议,约定了专利申请权和专利权归王某。根据《专利法》的规定,以下关于该项发明专利申请权和专利权归属的说法,正确的是()。
我国现行税法规定,扣缴义务人在代收车船税时,应在机动车交通事故责任强制保险的保险单上注明已收税款的信息,同时开具代扣代收税款凭证。()
下图是一个半圆形桥洞截面示意图,圆心为O,直径AB是河底线,弦GD是水位线,CD∥AB,且cD=24m,OE上cD于点E。已测得求半径OD;
Whatismeantbypastconsideration?
最新回复
(
0
)