This revised and updated textbook is, as before the study of plant and animal ecology, fully integrated and mathematical, and laborotory studies are described where necessary. Examples drawn from real ecological systems illustrate the complexity of this subject and the involvement of diverse areas - descriptive natural history, physiology, behaviour, field experimentation and mathematical modelling. The book attempts to encourage the reader to combine all the above facets, so that a balanced view emerges. Emphasis is placed on the clear presentation of mathematical aspects, and the material aims to be accessible to the undergraduate with little experience and also stimulating to practising ecologists. This new edition contains two new chapters both of which consider areas of applied ecology which are relevant to contemporary global issues. The first considers the control of abundance; on the one hand the limitingof pest and weed populations, on the other, maintaining the biological diversity of endangered species. Thesecond considers large areas as an extension of the discussion of communities. These "ecosystems" in the newest sense of the word are an important field of study when considering some of the important environmental problems facing mankind.