城市生态系统的主要特征有哪些？
参考答案：1、城市生态系统是人工生态系统，人类是其主体
①人类是城市生态系统的生产者，城市的一切设施都是人创造的；人类的生命活动是生态系统中能、物、信息流的一部分，具有自身再生产的过程。
②人类又是城市生态系统中的主要消费者，人类处在金字塔的顶端。
③人类还是城市生态系统的主宰者，人在此系统中既是调节者，也是被调节者。
2、城市生态系统容量大、流量大、密度高、运转快、是高度开放的生态系统
①城市生态系统所需求的大部分食物能量和物质，要依靠人工从其它生态系统人为输入。同时，城市生态系统中的生产、建设、交通、运输等都需要能量和物质供应。这些也必须从外界输入。
②城市生态系统的能流和物流可概括为五个过程：开采—制造—运输—使用—废弃
3、城市生态系统的脆弱性
①依靠外力维持
②城市生态系统在一定程度上破坏了自然调节机能
③食物链简化，系统自我调节能力小
④营养关系倒置，系统关系不稳定
4、市生态系统是人类自我驯化的系统5城市生态系统是多层次的复杂系统
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| E-schoolbags (电子书包) Is your schoolbag too heavy? The e-schoolbag will help you. It is said that e-schoolbags are going to be brought into 1 in Chinese middle schools soon. Heavy schoolbags have been a serious 2 for a long time. But the e-schoolbag will 3 . An e-school-bag is 4 lighter than a usual schoolbag. Perhaps, the e-schoolbag should be 5 an e-textbook. It is a small computer for students. It is as 6 as a usual book, 7 it can still have all the things for study, such as textbooks, exercise books and so on. They can be made 8 chips (芯片) like stamps. The students can read the text page by page on the screen (屏幕), take notes (记笔记), or even send e-mails to their. teachers. They only need to 9 the right chip into the e-schoolbag. Then they can use it. Some people say 10 e-textbooks can be easily broken, while others say it is not good to students' eyes. But only time will tell. | |||
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