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
2018-05-23
26
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://kaotiyun.com/show/yW6Z777K
0
考研英语一
相关试题推荐
Iftheonlineserviceisfreethenyouaretheproduct,technicianssay.GoogleandFacebookmakea【C1】______collectingpersonal
Thehighestanxietymomentintheholidayseasonmustbethemomentjustbeforeyourlovedonesunwraptheirgifts.Theribbonc
Thehighestanxietymomentintheholidayseasonmustbethemomentjustbeforeyourlovedonesunwraptheirgifts.Theribbonc
LastSeptember,theU.S.governmentannouncedthatitsbirthratefellto"anotherrecordlow".Morallyspeaking,there’snothing
It’sdifficulttoimagineaworldwithoutantibiotics.Theycurediseasesthatkilledourancestorsincrowds,andenableanynu
Judgingfromrecentsurveys,mostexpertsinsleepbehavioragreethatthereisvirtuallyanepidemicofsleepinessinthenatio
Judgingfromrecentsurveys,mostexpertsinsleepbehavioragreethatthereisvirtuallyanepidemicofsleepinessinthenatio
Thehappieryouare,thebetter,right?Notnecessarily.Studiesshowthatthereisadarkersidetofeelinggoodandthatthe【C
TheEU’sclimatechiefisseekingtoextendthebloc’srenewableenergytargets,inamoveapparentlydesignedtoprotectthegr
TheEuropeanUnionreachedapreliminarydealtocurbbanker’scompensationthatwoulddrasticallylimittheaccountthatcanbe
随机试题
“有神”之脉象主要是指:
从国际贸易支付工具的角度讲,票据主要包括( )。
期转现使买卖双方在确定期货平仓价格的同时,也确定了相应的现货买卖价格。()
某银行业从业人员在向客户销售理财产品时,故意混淆预期收益率与保证收益率的概念,并口头保证该产品肯定能够达到预期收益率。此行为违反了从业人员职业操守中的()。
生态学谬论:根据整体的分析结果去推断个体,认为个体具有整体的特征与属性。根据这个定义,下列不属于生态学谬论的是()。
一、注意事项 1.本试卷由给定资料与作答要求两部分构成。考试时限为150分钟。其中,阅读给定资料参考时限为40分钟,作答参考时限为110分钟。 2.一律用现代汉语在答题卡上作答。未按要求作答的,不得分。 3.请在答题卡上作答,严禁折叠答题卡!
光纤通信中使用的复用方式是(56)。E1载波把32个信道按(57)方式复用在一条2.048Mbit/s的高速信道上,每条话音信道的数据速率是(58)。
使用VC6打开考生文件夹下的源程序文件modi3.cpp,其中定义了用于表示雇员的Employee类,但类Employee的定义并不完整。请按要求完成下列操作,将类CEmployee的定义补充完成。(1)定义私有数据成员name、street、c
Lookatthelistbelow.Itshowsarangeofbusinessbooksavailablefromaninternetbookseller.Forquestions6-10ontheop
AFlattoLetAcomfortableflatwith3bedrooms,onedining-room,oneliving-roomandonebathroom,istolet.Theflatisloca
最新回复
(
0
)