THE STRUCTURE OF CLIMAXES 



237 



the contrary, aquatic sessile and sedentary animals resemble plants 

 more or less closely in all these respects. 



Influence. In the case of land animals, the chief effect is exerted 

 through coaction upon plants, and their role is commonly one of in- 

 fluence rather than of dominance. Although burrowing animals regu- 

 larly exercise a definite reaction upon soil, this rarely leads to the 

 destruction of the plant matrix. Modification of it is a more frequent 

 consequence, as exemplified by the hills of mound-making ants anrl 



Fig. 536. — An exclosure plot .showing the large growth of aspens at the edge of 

 a parklike opening, Kaibab forest, 1936, when protected from deer. (Courtesy 

 of the U. S. Forest Service, W. G. Mann, Supervisor.) The exclosure was 

 similar to the area shown in Fig. 53a at the time of fencing. (Photo by H. L. 



Andrews.) 



those in prairie-dog towns. Moreover, though influence may some- 

 times produce striking changes in the appearance of a community, as 

 in the short-grass condition of the mixed prairie, it does not often 

 lead to permanent transformation. Even in the short-grass com- 

 munity or disclimax, the mid grasses are regularly present in sup- 

 pressed form, and attain expression during wet phases at least. 



Influence is the outstanding characteristic of the animals of the 

 terrestrial biomes, and constitutes the basis for placing them in the 

 proper ecological relation to plants, as well as to each other. This 

 applies likewise to man under primitive conditions, especially before 



