①Plant communities assemble themselves flexibly, and their particular structure depends on the specific history of the area. Ecologists use the term “succession” to refer to the changes that happen in plant communities and ecosystems over time. The first community in a succession is called a pioneer community, while the long-lived community at the end of succession is called a climax community. Pioneer and successional plant communities are said to change over periods from 1 to 500 years. These changes-in plant numbers and the mix of species-are cumulative. Climax communities themselves change but over periods of time greater than about 500 years.
简单介绍了生态系统随着时间出现的几个阶段：先驱者，连接的植物群落，顶级群落。
② An ecologist who studies a pond today may well find it relatively unchanged in a year’s time. Individual fish may be replaced,but the number of fish will tend to be the same from one year to the next. We can say that the properties of an ecosystem are more stable than the individual organisms that compose the ecosystem.
生态系统的稳定性要比组成这个生态系统的单个个体的稳定性强。
③At one time, ecologists believed that species diversity made ecosystems stable. They believed that the greater the diversity the more stable the ecosystem. Support for this idea came from the observation that long-lasting climax communities usually have more complex food webs and more species diversity than pioneer communities. Ecologists concluded that the apparent stability of climax ecosystems depended on their complexity. To take an extreme example, farmlands dominated by a single crop are so unstable that one year of bad weather or the invasion of a single pest can destroy the entire crop.In contrast, a complex climax community, such as a temperate forest, will tolerate considerable damage from weather to pests.
生态学家认为生态系统的多样性越强，稳定性就越强。
④The question of ecosystem stability is complicated,however. The first problem is that ecologists do not all agree what “stability”means. Stability can be defined as simply lack of change. In that case, the climax community would be considered the most stable,since, by definition, it changes the least overtime.Alternatively,stability can be defined as the speed with which an ecosystem returns to a particular form following a major disturbance,such as a fire. This kind of stability is also called resilience. In that case, climax communities would be the most fragile and the least stable, since they can require hundreds of years to return to the climax state.
生态系统的稳定性是个复杂概念：稳定性=改变少，顶级群落最稳定；稳定性=恢复速度，顶级群落最脆弱。
⑤Even the kind of stability defined as simple lack of change is not always associated with maximum diversity. At least in temperate zones,maximum diversity is often found in mid-successional stages, not in the climax community. Once a redwood forest matures, for example, the kinds of species and the number of individuals growing on the forest floor are reduced. In general, diversity,by itself, does not ensure stability. Mathematical models of ecosystems likewise suggest that diversity does not guarantee ecosystem stability-just the opposite,in fact.A more complicated system is, in general, more likely than a simple system to break down.A fifteen-speed racing bicycle is more likely to break down than a child’s tricycle.
改变少和最大多样性没关系；多样性不能保证稳定性。
⑥Ecologists are especially interested to know what factors contribute to the resilience of communities because climax communities all over the world are being severely damaged or destroyed by human activities. The destruction caused by the volcanic explosion of Mount St.Helens, in the northwestern United States, for example,pales in comparison to the destruction caused by humans. We need to know what aspects of a community are most important to the community’s resistance to destruction, as well as its recovery.
人类牛逼啊，火山喷发造成的破坏和人类比起来真是小巫见大巫，并提出问题：对于群落对破坏的抵抗力和恢复力，什么因素最重要。
⑦Many ecologists now think that the relative long-term stability of climax communities comes not from diversity but from the “patchiness” of the environment; an environment that varies from place to place supports more kinds of organisms than an environment that is uniform. A local population that goes extinct is quickly replaced by immigrants from an adjacent community. Even if the new population is of a different species, it can approximately fill the niche vacated by the extinct population and keep the food web intact.
很多生态学家现在认为顶级群落的长期稳定性来源于环境的斑块分布。
