Chapter II 



THE STRUGGLE FOR EXISTENCE IN NATURAL 



CONDITIONS 



(1) Before beginning any experimental investigation of the ele- 

 mentary processes of the struggle for existence we must examine what 

 is the state of our knowledge of the phenomena of competition in 

 nature. The regularities which it has been possible to ascertain 

 there, and the ideas which have been expressed in their discussion, 

 will help us to formulate correctly certain fundamental requirements 

 for further experimental work. 



In thorough field observations the fact which strikes the investiga- 

 tor most of all is the extreme complexity of the communities of organ- 

 isms, and at the same time their possession of a definite structure. 

 On the one hand they undergo changes under the influence of external 

 environment, and on the other the slightest changes of some compo- 

 nents produce an alteration of others and lead to a whole chain of con- 

 sequences. It is difficult here to arrive at a sufficiently clear under- 

 standing of the processes of the struggle for existence. Elton writes 

 for instance: "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 competi- 

 tion? Or do changing conditions destroy or drive out the first arrival, 

 making thereby an empty niche for another animal which quietly 

 replaces it without ever becoming 'red in tooth and claw' at all? 

 Succession brings the ecologist face to face with the whole problem 

 of competition among animals, a problem which does not puzzle 

 most people because they seldom if ever think out its implications at 

 all carefully. At the present time it is well known that the American 

 grey squirrel is replacing the native red squirrel in various parts of 

 England, but it is entirely unknown why this is occurring, and no 

 good explanation seems to exist. In ecological succession among 

 animals there are thousands of similar cases cropping up, practically 

 all of which are as little accounted for as that of the squirrels" ('27, 

 p. 27-28). All this suggests that an analysis must be made of com- 

 paratively simple desert or Arctic communities where the number of 



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