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
2017-06-25
64
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.
【F1】
选项
答案
生态学家的使命就是调查清楚环境和生态因素长期以来是如何控制种群繁殖的内在能力的。
解析
转载请注明原文地址:https://kaotiyun.com/show/SXbZ777K
0
考研英语一
相关试题推荐
Psychologistshaveknownforacenturythatindividualsvaryintheircognitiveability.Butaresomegroups,likesomepeople,
Nationally,anageingpopulationisaproblem.Butlocallyitcanbeaboon.Theover-50scontrol80%ofBritain’swealth,and
Foryears,French,ItalianandAmericanluxurybrandshave【C1】______asChina’smiddleclassdevelopeda(n)【C2】______forhigh-en
Supposeyouarealibrarianinyouruniversity.Writeanoticeofabout100words,providingthenewly-enrolledinternationalst
Halfoftheworld’spopulationwillbespeakingorlearningEnglishby2015,researcherssay.Twobillionpeopleareexpectedto
Halfoftheworld’spopulationwillbespeakingorlearningEnglishby2015,researcherssay.Twobillionpeopleareexpectedto
Rumorhasitthatmorethan20booksoncreationism/evolutionareinthepublisher’spipelines.Afewhavealreadyappeared.【F1】
Itseemssimpleenoughtodistinguishbetweentheorganismandthesurroundingenvironmentandtoseparateforcesactingonano
【F1】Ican’thelpwonderingwhatCharlesDarwinwouldthinkifhecouldsurveythestateofhisintellectualachievementtoday.2
Severalweeksago.threeofthecountry’smostrespectedinstitutionsofhigherlearning,Harvard,Princeton,andtheUniversity
随机试题
1994年12月1日下午1时许,××地质学院家属××在挖冬贮菜窖时发现一口大缸,内有一“铜桶”(实际上铅罐),打开桶盖螺丝后,发现桶内有铅和石蜡,石蜡中有一用绳子拴着的“铜棒”(实际上是放射源)。在场人员以为发现了“宝物”,便取出相互传看,有人还用牙齿咬。
面部痛觉障碍在鼻尖及口周围最明显,外周稍差,其病变在
葛根芩连汤的功效是()
应是执业药师应具有药师或药学相关专业助理工程师(含)以上技术职称
下列有关商业银行解散的说法错误的是:()
全面质量管理是以()为基础的质量管理。
下列属于浙江省的民间信俗的有()。
我国的地产市场是土地使用权和所有权同时转让。()
有经验的司机完全有能力并习惯以120公里的时速在高速公路上安全行驶,为了迅速提高道路的使用效率,某条高速公路的最高时速限制由原来100公里转为120公里。以下各项如果为真,最能质疑上述主张的是()。
青花瓷发展的黄金时代是明朝永乐、宣德时期,与郑和下西洋在时间上重合,这不能不使我们思考:航海与瓷器同时达到鼎盛,仅仅是历史的偶然吗?从历史事实来看,郑和下西洋为青花瓷的迅速崛起提供了历史契机。近二三十年的航海历程推动了作为商品的青花瓷的大量生产与外销,不仅
最新回复
(
0
)