64 ANIMAL LIFE AND SOCIAL GROWTH 



rather than by changing numbers of invertebrates, 

 even though the latter have striking seasonal 

 significance. 



The composition of these communities indi- 

 cates that before the white man's influence be- 

 came so marked, the important, frequently the 

 predominant, influence in the community was 

 held by the larger mammals. In many cases this 

 influence was strong enough to control the distri- 

 bution of the dominant plants, in part at least. 

 With the coming of the white man, these passed 

 away and their place was taken either by man 

 and his domestic associates or by smaller, less 

 conspicuous mammals and by insects. In these 

 more northern communities, the role of the in- 

 sects does not seem, even today, to be as impor- 

 tant as that assigned to them after careful study 

 of their place in the Illinois communities. This 

 shift in importance may be due to the fact that the 

 Illinois countryside is more completely man- 

 controlled and that man has been able to control 

 the insect population less readily than that of the 

 mammals; or it may be that the warmer climate 

 enhances the importance of insects and of other 

 "cold-blooded" invertebrates. We know that in 

 the tropics, insects and insect-borne diseases are 

 of sufficient importance to keep even the white 

 man and his domestic animals from extensive and 

 otherwise attractive regions. 



