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
87
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.
【F5】
选项
答案
对那些变化不规则的种群,我们可能因为观察得不够而无法从繁多的“噪音”中提取信号。
解析
转载请注明原文地址:https://kaotiyun.com/show/EAK4777K
0
考研英语一
相关试题推荐
Americanhighereducationstandsonthebrink(边缘)ofchaos.1havesomanyspentsolonglearningsolittle.Thepresentcri
ShouldtheTreasurysellitseconomicforecastingcomputersforscrap?ForthepasttwoyearsnooneoutsidetheConservativePa
ShouldtheTreasurysellitseconomicforecastingcomputersforscrap?ForthepasttwoyearsnooneoutsidetheConservativePa
Toproducetheupheaval(激变)intheUnitedStatesthatchangedandmodernizedthedomainofhighereducationfromthemid-1860s
Cultureshockmightbecalledan【C1】______diseaseofpeoplewhohavebeensuddenly【C2】______abroad.Likemostailments,ithasi
Likemanyotheraspectsofthecomputerage,Yahoobeganasanidea,【C1】______intoahobbyandlatelyhas【C2】______intoafull-t
Predictionsoflargepopulationsofrobotsinindustryhaveyettocometrue.Foradecadeormore,manufacturersofbigrobots
Whenthesubjectismoney,womenoftenclingtotwopersistentstereotypes,oneapleasantdream,theotheranightmare.In
Lionsare【C1】______;theyprefertoeatwithouthavingtodotoomuchwork.Whenrestingintheshade,theyarealsowatchingth
Teachersneedtobeawareoftheemotional,intellectual,andphysicalchangesthatyoungadultsexperience.Andtheyalsoneed
随机试题
()抽油机井结构内没有套管。
求函数f(x,y)=3xy—x3一y3的极值.
最可能是乳腺纤维腺瘤的是最可能是乳腺脓肿的是
四逆散证的病机是
A.阴寒内盛,凝滞胃肠B.脾胃虚弱,清浊不分C.脾虚胃寒,失于温养D.阳气衰微,阴寒内结E.脾肺气虚,传送无力冷秘的病机为
桩基静载试验,总位移量大于或等于40mm,或本级荷载下沉量大于或等于前一级荷载下沉量的5倍,即可终止加载,该级荷载即为极限荷载。()
已知,则()
一项工作本来应该由你的同事去做,而同事现在有另外的任务,于是领导安排你接替同事的工作,同事回来后对你的工作不满意,请问你该怎么办?
某重点中学的学生中,有的是共青团员,有的不仅是共青团员,而且是校学生会干部。所有共青团员都是学习成绩良好的学生,所有成绩良好的学生都只遵守学校的规定。如果以上陈述为真,则以下哪项不一定为真?
虚拟设备是指
最新回复
(
0
)