STRUGGLE IN NATURAL CONDITIONS 



13 



components is small. Such a tendency to examine certain elemen- 

 tary phenomena is clearly seen in the following words of a Russian 

 zoologist, N. Severtzov, written as far back as 1855: "It seems to me 

 that the study of animal groupings in small areas, the study of these 

 elementary faunas is the firmest point of support for drawing conclu- 

 sions about the general laws regulating the distribution of animals 

 on the globe." 



However, besides this first possibility of studying competition phe- 

 nomena among a small number of components, an active intervention 

 into natural conditions by means of biotic experiments may also be 

 very important. Among such experiments the most frequent ones 

 consist in the transportation of animals into countries new to them, 

 which commonly leads to a great number of highly interesting proc- 



TABLE I 



Number of fir trunks on a unit of surface under different conditions 



From Sukatschev ('28) 



esses of the struggle for existence (Thomson, '22). The second type 

 of biotic experiments is an "exclusion" of the animal from a certain 

 community. Further on we give some examples of the struggle for 

 existence observed by such methods, but so far none of them have 

 been sufficiently studied. 



(2) It fell to the lot of botanists to have to deal with the simplest 

 conditions of competition, and they arrived at a very instructive con- 

 ception of the intensity of the struggle for existence. Foresters were 

 the first to be confronted with the question of competition when they 

 began to estimate the diminution in the number of tree trunks accom- 

 panying forest growth in different conditions of environment. They 

 characterize the struggle for existence by the percentage decrease in 

 the number of individuals on a unit of surface in a certain unit of 



