The first international congress for ecology took place in 1974 in The Hague, its central theme being "Unifying Concepts in Ecology". In the forefront of discussion at that time were questions of constancy, stability and resilience. Such questions have gone slightly out of fashion and the exceptionally precise and well thought-out concepts of that era are seldom applied nowadays. The present book introduces another unifying concept, the concept of the ecological cycle, or, more precisely, the mosaic-cycle concept of ecology. The following chapters have their origin in lectures which were held and discussed at a symposium of the Werner Reimers Stiftung in Bad Homburg. The purpose of the symposium