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
50
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://jikaoti.com/ti/vtMRFFFM
0
考研英语一
相关试题推荐
Americanhighereducationstandsonthebrink(边缘)ofchaos.1havesomanyspentsolonglearningsolittle.Thepresentcri
Toproducetheupheaval(激变)intheUnitedStatesthatchangedandmodernizedthedomainofhighereducationfromthemid-1860s
AnexpressionusedbyAmericansforabout100yearsis"topassthebuck".Itmeansrefusingtotakeresponsibility,lettingothe
Predictionsoflargepopulationsofrobotsinindustryhaveyettocometrue.Foradecadeormore,manufacturersofbigrobots
Whenthesubjectismoney,womenoftenclingtotwopersistentstereotypes,oneapleasantdream,theotheranightmare.In
Mostofthepeoplewhoappearmostoftenandmostgloriouslyinthehistorybooksaregreatconquerorsandgeneralsandsoldiers
Lionsare【C1】______;theyprefertoeatwithouthavingtodotoomuchwork.Whenrestingintheshade,theyarealsowatchingth
Americanwomenexperienceagreat【C1】______oflifestyles.A"typical"Americanwomanmaybesingle.Shemayalsobedivorcedor
WorkisaveryimportantpartoflifeintheUnitedStates.WhentheearlyProtestant【C1】______cametothiscountry,theybrough
KarlVonLinne(orLinnaeus,asheiswidelyknown)wasaSwedishbiologistwhodevisedthesystemofLatinisedscientificnames
随机试题
资产阶级革命派的局限性导致了辛亥革命的失败。下列关于资产阶级革命派自身局限性的说法错误的是()。
简述汉斯的比较教育思想。
下列施工质量控制的依据中,不属于专业技术性依据的是()。
某水利工程在施工过程中,根据监理单位的书面指示,施工单位进行了跨河公路桥基础破碎岩石开挖,但公路桥报价清单中无此项内容。主体工程报价清单中有以下单价:(1)混凝土坝工:砂卵石、岩石地基开挖70元/m3;Ⅱ:基础处理80元/m3(2)土石坝Ⅲ:砂卵石、岩石地
T+3滚动交收适用于()
《公司法》规定有限责任公司由()个以下股东出资设立,允许设立一人公司。
荷兰研究人员一直在试图模拟月球和火星的土壤条件进行农作物栽培实验。他们对该项实验种出的小红萝卜、豌豆、黑麦和西红柿进行初步分析。实验结果令人充满希望,这些产品不仅安全,而且可能比在地球上土壤种出的农作物更健康。英国媒体称,能在火星土壤种出可食用作物,殖民火
结合材料,回答问题:材料1犹记新中国成立之初,毛泽东豪迈展望,“一张白纸,没有负担,好写最新最美的文字,好画最新最美的画图”;犹记改革开放之初,邓小平在日本新干线列车上感受到“催人跑的意思”,沉思“我们现在正合适坐这样的车”。而当我们的
WaystoCreateColorsinaPhotographTherearetwowaystocreatecolorsinaphotograph.Onemethodcalledadditive,start
ItPaysofftoFocusonOneThingForthispart,youareallowed30minutestowriteanessaycommentingonthesaying"Bett
最新回复
(
0
)