小马托福阅读TPO9解析下载二.doc

小马托福阅读TPO19解析下载二
小马名师解析托福阅读TPO19文本下载二。下面为大家总结了小马名师解析的托福阅读TPO18文本,包括了答案解析,供同学们进行下载参考。
托福阅读TPO19文本解析
TPO19-1-2 原文:ession, Climax, and Ecosystems
In the late eenth century, ecology began to grow into an independent science from its roots in natural history and plant geography. The emphasis of this new "community ecology" was on position and structure munities
consisting of different species. In the early twentieth century, the American ecologist Frederic Clements pointed out that a ession of munities would develop after a disturbance such as a volcanic eruption, heavy flood, or
forest fire. An abandoned field, for instance, will be invaded essively by herbaceous plants (plants with little or no woody tissue), shrubs, and trees, eventually ing a forest. Light-loving species are always among the first
invaders, while shade-tolerant species appear later in the ession.
Clements and other early ecologists saw almost lawlike regularity in the order of ession, but that has not been substantiated. A general trend can be recognized, but the details are usually unpredictable. ession is influenced by
many factors: the nature of the soil, exposure to sun and wind, regularity of precipitation, chance colonizations, and many other random processes.
The final stage of a ession, called the climax by Clements and early ecologists, is likewise not predictable or of position. There is usually a good deal of turnover in position, even in a munity. The
nature of the climax is influenced by the same factors that influenced ession. Nevertheless, mature natural environments are usually in equilibrium. They change relatively little through time unless the environment itself changes.
For Clements, the climax was a "anism," anic entity. Even some authors who accepted the climax concept rejected Clements' characterization of it as a anism, and it is indeed a misleading metaphor. An ant colony may
be legitimately called a anism because munication system is so anized that the col