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
2016-03-22
59
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/NZsZ777K
0
考研英语一
相关试题推荐
Basically,AI(artificialintelligence)istheartofmakingmachinesappeartobeableto"think".Therearebasically,attheve
UFOsareunidentifiedflyingobjects,butnoonereallyknowswhattheyare.Manyresearchers(called"ufologists")havetheories
Newscientificstudiesrevealthehiddencostsofmultitaskingastechnologyincreasinglytemptspeopletodomorethanonethin
Newscientificstudiesrevealthehiddencostsofmultitaskingastechnologyincreasinglytemptspeopletodomorethanonethin
Newscientificstudiesrevealthehiddencostsofmultitaskingastechnologyincreasinglytemptspeopletodomorethanonethin
Itispredictedthattherewillbefourscientificbreakthroughsinthe21stcentury.We’llknowwherewecamefrom.Whydoe
[A]Whycan’tthishappenmoreoften?ItisnoaccidentthatWorthenandsomanyothersaredrawntoateacherwhoisnotalifel
[A]Notlongago,texting,alsocalledSMS,wasthedomainoftheyoung.Butnowitappearstohavejoinedtheletter,phone,fax
[A]Notlongago,texting,alsocalledSMS,wasthedomainoftheyoung.Butnowitappearstohavejoinedtheletter,phone,fax
Mothersinterferewiththeirchildren’slivesevenmorethanmostoffspringrealize.Thattheynagabouteatinghabitsiswellk
随机试题
某小规模纳税人采用销售额和销项税额合并定价法销售一批货物,销货款为20000元,则该次交易的应缴增值税额为
被称为恶病质素的细胞因子是
Ph染色体阳性对于下列哪种疾病的诊断有重要意义
标的证券为股票的,应当符合的条件有()。
某医院医生李某在为患者张某进行阑尾炎手术时,不慎将一块纱布遗留在张某的体内,张某在手术后连续数日疼痛难忍,再次检查时才发现纱布并重新手术取出。有关张某所受人身伤害的赔偿责任,下列说法正确的有()。
基准利率是在商业票据市场和同业拆借市场的交易中产生的。()
某沿海城市管辖A、B、C、D、E、F、G共7个县,这7个县的位置如图2所示。现用红、黑、绿、蓝、紫五种颜色给这7个县染色,要求任意相邻的两个县染不同颜色。则不同的染色方法有
线性表的顺序存储结构和线性表的链式存储结构分别是
FreeStatinsWithFastFoodCouldNeutralizeHeartRiskFastfoodoutletscouldprovidestatindrugsfreeof【C1】______sotha
WhyDepressionNeedsaNewDefinition[A]Manypsychiatristsbelievethatanewapproachtodiagnosingandtreatingdepression—li
最新回复
(
0
)