THE ECOLOGICAL SURVEY on which this book is based began to be planned in 1942, and since 1945 has been mainly centred upon Oxford University's estate at Wytham Woods, where a rich series of habitats from open ground and limestone to woodland with many springs and marshes interspersed occupies a hill set in riverine surroundings. Here biological research workers from the University have accumulated a considerable body of knowledge, some of which I have arranged in a general setting that allows one to comprehend some of the inter-related parts of the whole system. It is also intended to provide a framework for understanding animal communities elsewhere. The ecological inquirer is, more than most scien tific people, apt to fmd himself lost in a large labyrinth of interrelations and variables. The dictionary defmes a labyrinth as 'an intricate structure of inter communicating passages, through which it is difficult to fmd one's way without a clue'. This could equally be a figurative description of plant and animal communi ties. The present book seeks to provide a plan of construction of the labyrinth and a few new clues that may help the inquirer to know where he is on the gene ral ecological map. In presenting this blue-print of animal communities I have avoided giving long lists of species such as the botanist, with his smaller kingdom, can handle fairly well."

n this book I have tried to bring together ideas from three different Istreams of thought with which I have been closely concerned during the last thirty years or so. The first is faunal history, usually regarded as a purely academic subject, but to some of whose events can be traced a number of the serious dislocations taking place in the world today. The second is ecology, particularly the structure and dynamics of populations. The third is conservation. I first published a few ideas about the signifi cance of invasions in 1943, in a war-time review called Polish Science and Learning, under the title of 'The changing realms of animal life'. Since then I have had the opportunity to think pretty hard about conservation, while taking part in the planning and development of the Nature Con servancy. In March 1957 I gave three broadcasts in the B. B. C. 's Third Programme, under the title of 'Balance and Barrier'. These were sub sequently printed in The Listener (1957, Vol. 57, pp. 514-15,556-7,596-7, and 600). The present book is essentially an expansion of these. I am extremely grateful to Mr James C. Thornton and Dr John Simons for in planning and giving these talks. advice and help In preparing this book I have had invaluable assistance from the staff of the Bureau of Animal Population. Miss C. M. Gibbs typed the fair copy. Miss M."