viii AUTHOR'S PREFACE 



problems (most of whom, it may be noted, were not trained 

 as professional zoologists), and partly because the principles 

 of animal ecology are seldom if ever mentioned in zoological 

 courses in the universities, in spite of the fact that it is just 

 such knowledge which is required by any one who is brought 

 up against practical problems in the field, after he leaves the 

 university. Ecology is a branch of zoology which is perhaps 

 more able to offer immediate practical help to mankind than 

 any of the others, and in the present rather parlous state of 

 civilisation it would seem particularly important to include 

 it in the training of young zoologists. Throughout this book 

 I have used analogies between human and animal communities. 

 These are simply intended as analogies and nothing more, 

 but may also help to drive home the fact that animal interrela- 

 tions, which after all form the more purely biological side of 

 ecology, are very complicated, but at the same time subject 

 to definite economic laws. 



Finally, I wish to point out that no attempt has been made 

 to provide a handbook containing references to all the ecological 

 work that has ever been done, since such a work would be 

 both exhausting to read, and useless when it had been read. 

 I have simply taken the various principles and ideas and 

 illustrated them by one or two examples. 



I am indebted to Mr. O. W. Richards for a great deal of 

 help and criticism. Many of the ideas in this book have been 

 discussed with him, and gained correspondingly in value, and 

 in particular his extensive knowledge of insects has been 

 invaluable in suggesting examples to illustrate various points. 

 The list of works dealing with British insects was compiled 

 with his aid. 



I am also indebted to Professor J. S. Huxley for much help- 

 ful advice, and I have to thank Dr. T. G. Longstaff, Dr. K. S. 

 Sandford, and Captain C. R. Robbins, for allowing me to use 

 photographs, all taken in rather out-of-the-way parts of the 

 world (Spitsbergen, Egyptian desert, and Burma, respectively). 



CHARLES ELTON. 



University Musewm, 

 Oxford. 



