67 



THE ASSOCIATIONS OF THE SAND PRAIRIE 



The classification of the associations and the description of the 

 plants are based upon the work of Glcason ('lo), with the exception 

 of the discussion of the black-soil transition association and the 

 blovvsand complex. From the botanical view-point the associations 

 are quite distinct from one another, and a study of the animals shows 

 a definite demarcation of the different animal assemblages as well. 

 The ability of the animals to move about, however, makes ihe con- 

 ditions for study more complex. 



The animals of the sand prairie are characteristically terrestrial, 

 as surface water is almost absent from sand. The scarcity of humus 

 excludes most animals lower in the taxonomic scale than spiders, and 

 the most abundant animals are insects, both as regards species and 

 individuals. Reptiles and birds are not abundant. The larger mam- 

 mals are no longer present, owing to the encroachment of civilization. 



The sand prairie is composed of two formations, the prairie for- 

 mation, and the blowout formation. 



Method of Analysis of the Animal Assemblages 



The animals have been classified primarily according to kind of 

 food; secondarily according to those behavior characters which ef- 

 fect distribution within the association. The major space-divisions 

 within an association correspond to the horizontal strata in w^hich 

 animals live. (Cf. Shelford, 'lib: 602.) In the sand prairie these 

 are four : the air, the plant, the ground, and the underground layers. 

 The animals which live in these strata have been called aericolous, 

 hcrbicolous, tcrricoloiis, and subferricolous. In determining which 

 stratum an animal belongs in, the one in which it obtains its food 

 has usually been selected, though for other activities the animal more 

 frequently seeks some other level. The tertiary division is based 

 upon the flexibility or non-flexibility of habits, particularly food- 

 habits. Animals of very restricted food-habits are found to be of 

 much less importance than those which take different kinds of food. 



Knowledge of the habits of many of the animals studied is very 

 imperfect, and for this reason the different groups in the classification 

 have not been subdivided to the same extent. In some cases the divi- 

 sions can be made with considerable accuracy ; in others the different 

 ecological types can not at present be separated. In certain groups of 

 only a few animals, minute subdivision would be cumbersome, and 

 has not been attempted. 



