25个考研英语阅读经典试题及答案(15).pdfVIP

25个考研英语阅读经典试题及答案(15) 宫东风 25 个考研英语阅读经典试题及答案(15)第 1 页：试题第 2 页：答案与考点解析李剑考研英语相似易混单词对比记忆 31 天升 级版 SAMPLE 15 [生态学] 题目序号 题型归类 第 1 题 中心主旨题型 第 2 题 细节推导题型 第 3 题 审题定位与中心主旨题型 第 4 题 归纳推导题型 第 5 题 写作手法题型 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 第 1 页 共 9 页 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 ho severely or unpredictably birth, death, and migration rates 第 2 页 共 9 页 may be fluctuating around their long-term averages, if there were no density-depende