ECOLOGICAL SUCCESSION 27 



communities of animals, showing that the animals are in this 

 case affected rather by the food, shelter, etc., provided by the 

 heather than by the general physical " climate " produced by 

 the pine wood.^^^ It is when we try to work out the food 

 relations of the animals that the presence of small patches of 

 earher pioneer animals in a climax association becomes such a 

 complicating factor. In fact, succession (at any rate in animals) 

 does not take place with the beautiful simplicity which we 

 could desire, and it is better to realise this fact once and for 

 all rather than to try and reduce the whole phenomenon to a 

 set of rules which are always broken in practice ! The present 

 state of our knowledge of succession is very meagre, and this 

 ignorance is to a large extent due to lack of exact knowledge 

 about the factors which Hmit animals in their distribution and 

 numbers. The work done so far has necessarily been re- 

 stricted to showing the changes in exclusive species of one 

 genus, or in the picking out of one or two salient features in 

 the changes as an indication of the sort of thing that is taking 

 place. Work like that done by Shelf ord, and observations like 

 those of Ritchie and Massart, make it quite clear that succession 

 is an important phenomenon in animal Hfe ; the next stage of 

 the inquiry is the discovery of the exact manner in which 

 succession affects whole communities. 



13. It will be as well at this point to remind the reader that 

 most of the work done so far upon animal succession has been 

 static and not dynamic in character ; that the cases in which 

 the whole thing has been seen to happen are few in number 

 and, although extremely valuable and interesting, of necessity 

 incompletely worked out. 



Given a good ecological survey of animal communities and 

 a knowledge of the local plant seres, we can predict in a general 

 way the course of succession among the animals, but in doing 

 so we are in danger of making a good many assumptions, and 

 we do not get any clear conception of the exact way in which 

 one species replaces another. Does it drive the other one out 

 by competition ? and if so, what precisely do we mean by 

 competition ? Or do changing conditions destroy or drive 

 out the first arrival, making thereby an empty niche for another 



