The wealth of the natural sciences no longer consists in the abundance of facts, but in the way they are linked together. ALEXANDER VON HUMBOLDT There is no dearth of books on ecology. Why write yet another? Each person is different, and each views the problems in a different way. Each emphasizes different aspects and describes them in a different style. When I was a student I often found certain books more helpful than others, and I still think it is useful to have a variety of presentations from which to choose. This variety also allows the student to appreciate the diversity within the field of ecology. I have devoted considerable effort to making this book readable. Throughout I have refrained from using specialized terminology - thus also avoiding the problem that many terms are used differently in the various areas of ecology. Straightforward English is quite sufficient to describe complicated situations. Furthermore, precisely defined terms are usually associated with detailed quantitative descriptions, whereas we are concerned with a general understanding of the dynamics of ecology. For similar reasons I have tried to rely as little as possible on mathematical discussions. All too often, in recent years, people have overlooked the fact that mathematics - like language - can give only a description, albeit an especially precise one.