This is an inadvertent book, though it did arise naturally enough from a course I give in theoretical ecology. But I wouldn't have given the course at all if one colleague in my department hadn't left for a leave of absence, while another abruptly resigned. This propelled me to the fore where this teaching responsibility was concerned, one I had never had any intention of discharging. Then it turned out that one of my students was regularly unable to make half the classes. As a result, I began giving him my lecture notes each week. As I knew that someone else would be reading them, I began to write my notes more carefully. Naturally enough, the other students soon began to demand the notes too. Eventually they were indulged. Thus I found myself writing a textbook manuscript. By the next year, the students were handed all their notes in one package at the outset. But these were still just hand-written. Inevitably, the demand that they be typed arose. This I didn't want to do until I found a publisher. As it turned out, Tim Hardwick of Croom Helm was willing to have his firm fill this role, to my great satisfaction. • and his considerable frustration. I have been a desultory author about producing this final text, and can only express my gratitude for his enduring patience over more than 18 months of delays.