Ecologists 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 communitys resistance to destruction, as well as its recovery.
Many 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.
Paragraph 1: Plant 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 changesin plant numbers and the mix of speciesare cumulative. Climax communities themselves change but over periods of time greater than about 500 years.
【TPO托福阅读真题答案及解析(1)】相关文章:
★ 牛津小学英语三年级说课稿 Unit5 B Let’s talk
最新
2016-03-02
2016-03-02
2016-03-02
2016-03-02
2016-03-02
2016-03-02