DISTRIBUTION OF ANIMAL COMMUNITIES 17 



gradients in the environment and all the different communities 

 of animals which inhabit them. One habitat alone, the edge 

 of a pond, or the ears of mammals, would require a whole 

 book if it were to be treated in an adequate way. The aim 

 of the foregoing sketch of the whole subject is to show that the 

 term " animal community " is really a very elastic one, since 

 we can use it to describe on the one hand the fauna of equatorial 

 forest, and on the other hand the fauna of a mouse's caecum. 



For general descriptions of the animal communities of 

 the more important habitats, the reader may be referred to a 

 book on animal geography by Hesse,^^^ and to a more recent 

 book by Haviland.^^^ 



15. The attention of ecologists has been directed hitherto 

 mainly towards describing the differences between animal 

 communities rather than to the fundamental similarity between 

 them all. The study of these differences forms a kind of 

 animal ethnology, while the study of the resemblances may be 

 compared to human sociology (soon to become social science). 

 As a matter of fact, although a very large body of facts of the 

 first type has been accumulated, few important generalisations 

 have as yet been made from it. So much is this the case that 

 many biologists view with despair the prospect of trying to 

 learn anything about ecology, since the subject appears to them 

 at first sight as a mass of uncoordinated and indigestible 

 facts. It is quite certain that some powerful digestive juice 

 is required which will aid in the assimilation of this mass of 

 interesting but unrelated facts. We have to face the fact that 

 while ecological work is fascinating to do, it is unbearably dull 

 to read about, and this must be because there are so many 

 separate interesting facts and tiny problems in the lives of 

 animals, but few ideas to link the facts together. It seems 

 certain that the key to the situation lies in the study of animal 

 communities from the sociological point of view. This branch 

 of ecology is treated in Chapter V., but first of all it is necessary 

 to say something about the subject of ecological succession — 

 an important phenomenon discovered by botanists, since it 

 enables us to get a fuller understanding of the distribution 

 and relations of animal and plant communities. 



c 



