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
考研
As Gilbert White, Darwin, and others observed long ago, all species appear to have the innate capacity to increase their numbers
As Gilbert White, Darwin, and others observed long ago, all species appear to have the innate capacity to increase their numbers
admin
2014-10-27
46
问题
As Gilbert White, Darwin, and others observed long ago, all species appear to have the innate capacity to increase their numbers from generation to generation.【F1】
The task for ecologists is to untangle the environmental and biological factors that hold this intrinsic capacity for population growth in check over the long run.
The great variety of dynamic behaviors exhibited by different population makes this task more difficult: some populations remain roughly constant from year to year; others exhibit regular cycles of abundance and scarcity; still others vary wildly, with outbreaks and crashes that are in some cases plainly correlated with the weather, and in other cases not.
To impose some order on this kaleidoscope of patterns, one school of thought proposes dividing populations into two groups. These ecologists posit that the relatively steady populations have density-dependent growth parameters; that is, rates of birth, death, and migration which depend strongly on population density.【F2】
The highly varying populations have density-independent growth parameters, with vital rates buffeted by environmental events; these rates fluctuate in a way that is wholly independent of population density.
This dichotomy has its uses, but it can cause problems if taken too literally. For one thing, no population can be driven entirely by density-independent factors all the time. No matter how severely or unpredictably birth, death, and migration rates may be fluctuating around their long-term averages, if there were no density-dependent effects, the population would, in the long run, either increase or decrease without bound(barring a miracle by which gains and losses canceled exactly).【F3】
Put another way, it may be that on average 99 percent of all deaths in a population arise from density-independent causes, and only one percent from factors varying with density.
The factors making up the one percent may seem unimportant, and their cause may be correspondingly hard to determine. Yet, whether recognized or not, they will usually determine the long-term average population density.
In order to understand the nature of the ecologist’s investigation, we may think of the density-dependent effects on growth parameters as the signal ecologists are trying to isolate and interpret, one that tends to make the population increase from relatively low values or decrease from relatively high ones, while the density-independent effects act to produce noise in the population dynamics.【F4】
For populations that remain relatively constant, or that oscillate around repeated cycles, the signal can be fairly easily characterized and its effects described, even though the causative biological mechanism may remain unknown.
【F5】
For irregularly fluctuating populations, we are likely to have too few observations to have any hope of extracting the signal from the overwhelming noise.
But it now seems clear that all populations are regulated by a mixture of density-dependent and density-independent effects in varying proportions.
【F3】
选项
答案
换一句话讲,也许种群内平均99%的死亡都由“种群密度无关”因素导致的,只有1%和种群密度有关。
解析
转载请注明原文地址:https://jikaoti.com/ti/ktMRFFFM
0
考研英语一
相关试题推荐
Themostexcitingkindofeducationisalsothemostpersonal.Nothingcan【C1】______thejoyofdiscoveringforyourselfsomethin
Thegovernmentistobanpaymentstowitnessesbynewspapersseekingtobuyuppeopleinvolvedinprominenteases【C1】______thet
Likemanyotheraspectsofthecomputerage,Yahoobeganasanidea,【C1】______intoahobbyandlatelyhas【C2】______intoafull-t
Whenthesubjectismoney,womenoftenclingtotwopersistentstereotypes,oneapleasantdream,theotheranightmare.In
Whenthesubjectismoney,womenoftenclingtotwopersistentstereotypes,oneapleasantdream,theotheranightmare.In
What’syourearliestchildhoodmemory?CanyourememberlearningtowalkOrtalk?Thefirsttimeyou【C1】______thunderorwatched
Consumersandproducersobviouslymakedecisionsthatmoldtheeconomy,butthereisathirdmajor【C1】______toconsidertherole
Mostofthepeoplewhoappearmostoftenandmostgloriouslyinthehistorybooksaregreatconquerorsandgeneralsandsoldiers
Americanwomenexperienceagreat【C1】______oflifestyles.A"typical"Americanwomanmaybesingle.Shemayalsobedivorcedor
随机试题
WhichofthefollowingthatareconcernedwithPresidentFranklinD.Rooseveltisnottrue?()
患者,女性,23岁,风湿性心脏病,二尖瓣狭窄病史5年,本次因气急、咳嗽、咯粉红色泡沫痰2小时,拟诊急性肺水肿入院。根据上述表现,估测其肺血管病变程度及右心功能状况属于
慢性肺心病急性发作最常见的诱因是
下列关于承包人承担的义务,叙述不正确的是()。
案例十八:某企业从事某项投资活动的年投资收益率为10%。现有两个投资方案如下:甲方案:第一年缴纳企业所得税100万元的概率为20%,纳税150万元的概率为50%,纳税180万元的概率为30%;第二年纳税120元的概率为40%,纳税160万元的概率为40%
某企业目前处于成熟发展阶段,公司目前的资产总额为10亿元,所有者权益总额为6亿元,其中股本2亿元,资本公积2亿元,负债总额为4亿元,公司未来计划筹集资本1500万元,所得税税率为25%,银行能提供的最大借款限额为500万元,假设股票和债券没有筹资限额。备
质量成本包括()。
下列句子有语病的一项是()。
根据行政诉讼法及有关司法解释的规定,裁定主要适用于()。
Inthemedicalprofession,technologyisadvancingsofastthatquestionsoflawandethicscannotbediscussedandansweredfas
最新回复
(
0
)