In order to understand the nature of the ecologists 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.

【考研英语阅读分析详解例15】相关文章：

★ 英语四级考试阅读理解考前备战

★ 英语四级阅读难句解析二

★ 英语四级阅读理解模拟题及答案详解18

★ 大学英语四级阅读理解练习题（1）

★ 英语六级阅读最后的冲刺名师解答常见难题

★ 英语四级阅读：主旨题解题思路

★ 英语四级考试阅读备考材料(2)

★ 09年6月英语六级阅读考试的分析

★ 英语四级阅读难句解析汇总

★ 英语四级考试阅读习题及答案解析(2)