No. 571] TERRESTRIAL ASSOCIATIONS 



135 



animal populations. Certain of the animal assemblages 

 of sand habitats, as studied in central Illinois, intergrade; 

 others, as oak forest and bunch-grass, differ radically. 



The above considerations, if correct, appear to signify 

 that, in ordinary climatic development of plant and ani- 

 mal life in temperate land environments, the area of the 

 animal assemblage is that of the plant assemblage, both 

 resting basically upon the physical environment. The 

 plant and animal assemblages are therefore coextensive 

 parts of a biotic association, composed of both plants 

 and animals, and this association as a whole constitutes 

 the real terrestrial community of living organisms. 



B. Local Relations of Plant and Animal Assemblages 

 (Relations Within the Association) 



The more intimate relations between plants and ani- 

 mals are seen in the detailed study of a single associa- 

 tion. The bunch-grass association of sand prairie is 

 selected for illustration (E: 68). 



1. Similarity of Ecological Type of Plants and Ani- 

 mals.-— Shelford has shown (A: 593-594) that animals 

 and plants may evince ecological similarity by similar 

 response to the same general environmental conditions, 

 behavior responses in animals 7 corresponding to struc- 

 tural responses in plants, 8 so that mores of the animal 

 may be in accord with growth-form in the plant. Shel- 

 ford states (B: 87) that " plants and animal communities 

 are in full agreement when the growth-form of each- 

 stratum of the plant-community is correlated with the 

 conditions selected by the animals of that stratum." 



In the bunch-grass there is general agreement, ac- 

 cording to this criterion. The herbaceous stratum is oc- 

 cupied mainlv bv tuft and mat plants— bunch-grasses, 

 cactus and a few half-shrubs. Associated with the tuft or 

 mat growth-form is the sedentary mores of the plant- 

 inhabiting animals (leaf-beetles, stem-borers, ambush- 



