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. 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. 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). 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. 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. 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.
1. The author of the text is primarily concerned with ______.
2. It can be inferred from the text that the author considers the dichotomy discussed to be ______.
3. According to the text, all of the following behaviors have been exhibited by different populations EXCEPT ______.
4. The discussion concerning population in the third paragraph serves primarily to ______.
5. In the text, the author does all of the following EXCEPT ______.
问题1选项
A.discussing two categories of factors that control population growth and assessing their relative importance
B.describing how growth rates in natural populations fluctuate over time and explaining why these changes occur
C.proposing a hypothesis concerning population size and suggesting ways to test it
D.posing a fundamental question about environmental factors in population growth and presenting some currently accepted answer
问题2选项
A.applicable only to erratically fluctuating populations
B.instrumental, but only if its limitations are recognized
C.dangerously misleading in most circumstances
D.a complete and sufficient way to account for observed phenomena
问题3选项
A.roughly constant population levels from year to year
B.regular cycles of increases and decreases in numbers
C.erratic increases in numbers correlated with the weather
D.unchecked increases in numbers over many generations
问题4选项
A.demonstrate the difficulties ecologists face in studying density-dependent factors limiting population growth
B.advocate more rigorous study of density-dependent factors in population growth
C.prove that the death rates of any population are never entirely density-independent
D.underline the importance of even small density-dependent factors in regulating long-term population densities
问题5选项
A.cite the views of other biologists
B.define a basic problem that the text addresses
C.present conceptual categories used by other biologists
D.describe the results of a particular study
第1题:A
第2题:B
第3题:D
第4题:D
第5题:D
第1题:
【选项释义】
The author of the text is primarily concerned with ______. 本文的作者主要关注______。
A. discussing two categories of factors that control population growth and assessing their relative importance A. 讨论控制人口增长的两类因素,并评估它们的相对重要性
B. describing how growth rates in natural populations fluctuate over time and explaining why these changes occur B. 描述自然种群的增长率如何随时间波动,并解释为什么会发生这些变化
C. proposing a hypothesis concerning population size and suggesting ways to test it C. 提出关于种群规模的假设并提出检验方法
D. posing a fundamental question about environmental factors in population growth and presenting some currently accepted answer D. 提出一个关于人口增长中的环境因素的基本问题,并给出一些目前被接受的答案
【考查点】主旨大意题。
【解题思路】文章首先提出物种增长的现象,随即提出二分法并对其进行讨论,最后对这个二分法进行评估,因此在这篇文章中,作者主要关注的是讨论控制人口增长的两类因素以及他们的重要性,所以A项“讨论控制人口增长的两类因素,并评估它们的相对重要性”符合题意。
【干扰项排除】B项“描述自然种群的增长率如何随时间波动,并解释为什么会发生这些变化”、C项“提出关于种群规模的假设并提出检验方法”和D项“提出一个关于人口增长中的环境因素的基本问题,并给出一些目前被接受的答案”都是文章中的一部分,不够全面,这三项属于以偏概全。
第2题:
【选项释义】
It can be inferred from the text that the author considers the dichotomy discussed to be ______. 从文中可以推断,作者认为讨论的二分法______。
A. applicable only to erratically fluctuating populations A. 只适用于不稳定波动的人口
B. instrumental, but only if its limitations are recognized B. 有用的,但前提是它的局限性被认识到
C. dangerously misleading in most circumstances C. 在大多数情况下都是危险的误导
D. a complete and sufficient way to account for observed phenomena D. 解释观察到的现象的一种完整而充分的方法
【考查点】推理判断题。
【解题思路】根据关键词dichotomy定位至第三段首句“这种二分法有它的用途,但如果从字面上理解,就会产生问题(but it can cause problems if taken too literally)”,其中二分法指的是第二段提到的两类种群,即相对稳定的种群和高度变化的种群,第二段讨论了这两种种群的不同用途,说明二分法是有用的;然后第三段首句却提到but it can cause problems if taken too literally(但如果从字面上理解,就会产生问题),可以看出,二分法有其局限性,所以B项“有用的,但前提是它的局限性被认识到”符合题意。
【干扰项排除】
A项“只适用于不稳定波动的人口”表述太绝对,该项属于曲解原文;
C项“在大多数情况下都是危险的误导”和D项“解释观察到的现象的一种完整而充分的方法”表述都比较片面,这两项属于以偏概全。
第3题:
【选项释义】
According to the text, all of the following behaviors have been exhibited by different populations EXCEPT ______. 根据本文,以下所有的行为都在不同的物种中出现过,除了______。
A. roughly constant population levels from year to year A. 每年大致保持恒定的人口水平
B. regular cycles of increases and decreases in numbers B. 数字有规律的增加和减少的循环
C. erratic increases in numbers correlated with the weather C. 数量的不稳定增长与天气有关
D. unchecked increases in numbers over many generations D. 数代人不受制约的增长
【考查点】细节事实题。
【解题思路】根据首段前两句“正如吉尔伯特•怀特、达尔文和其他人很久以前观察到的那样,所有物种(all species)似乎都具有与生俱来的能力,能够一代一代地增加它们的数量。生态学家的任务是理清环境和生物因素,从长远来看,这些因素制约着(in check)人口增长的内在能力”,其中all species对应了题干中的different populations,可知不同的物种都具有能够一代一代地增加它们的数量的能力,但是这种能力受到环境和生物因素的制约,D项“数代人不受制约的增长”中的unchecked与原文不符合,但符合题干,故该题选择D项。
【干扰项排除】
A项“每年大致保持恒定的人口水平”、B项“数字有规律的增加和减少的循环”和C项“数量的不稳定增长与天气有关”,根据第一段最后一句“不同种群表现出的各种动态行为使得这项任务更加困难:有些种群年复一年大致保持不变;另一些则表现出规律性的丰富性和稀缺性循环;还有一些情况差别很大,疾病的爆发和崩溃在某些情况下与天气密切相关,而在其他情况下则与天气无关”可知,这三项行为都在不同的物种中出现过,故属于反向干扰。
第4题:
【选项释义】
The discussion concerning population in the third paragraph serves primarily to ______. 第三段中关于种群的讨论主要是为了______。
A. demonstrate the difficulties ecologists face in studying density-dependent factors limiting population growth A. 说明生态学家在研究限制种群增长的密度依赖因素时所面临的困难
B. advocate more rigorous study of density-dependent factors in population growth B. 提倡更严格地研究种群增长中密度依赖的因素
C. prove that the death rates of any population are never entirely density-independent C. 证明任何种群的死亡率都不是完全与密度无关的
D. underline the importance of even small density-dependent factors in regulating long-term population densities D. 强调即使是很小的密度依赖因素在调节长期的种群密度方面的重要性
【考查点】推理判断题。
【解题思路】首先定位第三段,该段主要陈述density-dependent factors(密度依赖因素),由最后三句“换句话说,种群中平均99%的死亡是由与密度无关的原因引起的,只有1%是随密度变化的因素引起的。构成这1%的因素可能看起来不重要,它们的原因可能相应地难以确定。然而,无论是否被认识到,它们通常将决定长期的平均种群密度。”可知,种群中只有1%的死亡是由密度依赖因素引起,但是这1%的因素通常决定长期的平均种群密度,综合理解可以推断,第三段关于种群的讨论主要是为了强调密度依赖因素在调节种群密度方面的重要性,D项“强调即使是很小的密度依赖因素在调节长期的种群密度方面的重要性”符合题意。
【干扰项排除】
A项“说明生态学家在研究限制种群增长的密度依赖因素时所面临的困难”在第三段没有依据,该项属于无中生有;
B项“提倡更严格地研究种群增长中密度依赖的因素”,该段只是证明了种群增长中密度依赖因素的重要性,但是advocate在该段没有体现,该项属于无中生有;
C项“证明任何种群的死亡率都不是完全与密度无关的”并不是第三段讨论种群的重点,该项属于本末倒置。
第5题:
【选项释义】
In the text, the author does all of the following EXCEPT ______. 在本文中,作者做了以下所有的事情,除了______。
A. cite the views of other biologists A. 引用其他生物学家的观点
B. define a basic problem that the text addresses B. 定义文章要解决的一个基本问题
C. present conceptual categories used by other biologists C. 介绍其他生物学家使用的概念范畴
D. describe the results of a particular study D. 描述一项特定研究的结果
【考查点】推理判断题。
【解题思路】通读全文可知,本文作者在论述自己的观点时运用了各种写作手段,第一段引用生物学家的观点引出文章主题,第二段介绍其他生态学家所定义的概念,第三段和第四段则是提出二分法需要解决的一个问题,并介绍理解生态学家们所从事的研究的性质的不同方法,只有D项“描述一项特定研究的结果”的写作手法并没有在文中运用,故该题选择D项符合题意。
【干扰项排除】
A项“引用其他生物学家的观点”在第一段有体现,该段引用了吉尔伯特•怀特和达尔文,该项属于反向干扰;
B项“定义文章要解决的一个基本问题”在第三段有体现,第一句提到“这种二分法有它的用途,但如果从字面上理解,就会产生问题”,该项属于反向干扰;
C项“介绍其他生物学家使用的概念范畴”在第二段有体现,第一句提到“为了给这种千变万化的模式赋予一些秩序,一种思想学派建议将种群分为两类”,该项属于反向干扰。