秒速飞艇技巧

江西考研

考试类型

热点推荐

您现在的位置:秒速飞艇技巧 > 考研 > 考试题库 >

2020考研英语阅读冲刺模拟及答案(2)

2019-10-31 14:43:53| 江西中公教育

完形填空是考研比较难的一部分,从历年的平均分可看出,每年平均分都在5分左右,低于及格分。复习完形建议高质量练习。把完形出现的固定搭配、固定词组整理出来,一般在9月后开始系统准备、做题为宜。江西中公考研小编整理了“2020考研英语阅读冲刺模拟及答案(2)”的文章,希望对大家有所帮助。

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.

秒速飞艇技巧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

[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.

2.It can be inferred from the text that the author considers the dichotomy discussed to be

秒速飞艇技巧[A] applicable only to erratically fluctuating populations.

[B] instrumental, but only if its limitations are recognized.

秒速飞艇技巧[C] dangerously misleading in most circumstances。

[D] a complete and sufficient way to account for observed phenomena.

3。According to the text, all of the following behaviors have been exhibited by different populations EXCEPT

[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。

4.The discussion concerning population in the third paragraph serves primarily to

[A] demonstrate the difficulties ecologists face in studying density-dependent factors limiting population growth.

秒速飞艇技巧[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.

5. In the text, the author does all of the following EXCEPT

秒速飞艇技巧[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.

1 2

 注:本站稿件未经许可不得转载,转载请保留出处及源文件地址。
(责任编辑:刘嗣业)

推荐课程

¥16800.00
¥4280.00
¥7180.00

免责声明:本站所提供试题均来源于网友提供或网络搜集,由本站编辑整理,仅供个人研究、交流学习使用,不涉及商业盈利目的。如涉及版权问题,请联系本站管理员予以更改或删除。

微信公众号
微博二维码
咨询电话(9:30-23:30)

秒速飞艇技巧400 6300 999

在线客服 点击咨询

投诉建议:400 6300 999

福建快3投注 安徽快3走势 秒速快三走势 秒速快三计划 秒速飞艇开户 极速时时彩开奖 秒速飞艇计划 秒速飞艇平台 山东十一运夺金开奖结果 秒速飞艇计划