68 



It is to be remembered that larva and adult of a particular species 

 may he quite dissimilar ecologically, each having a different status 

 in the association. The habits of many animals may vary widely ; 

 thus most of the sand-prairie birds eat both animal and vegetable 

 material, and are accordingly listed with both phytophagous and 

 predaceous animals. 



Doininant animals are those of considerable importance in the 

 association. In the lists of animals of the various associations, an 

 asterisk denotes that the species is a dominant form. 



The Prairie Formation 



The important ecological feature of the prairie formation is the 

 control of the physical environment by the vegetation. Though the 

 formation is open, it is usually quite stable, and the processes at 

 work tend toward the binding of the sand, the gradual enrichment 

 of the soil through the accumulation of humus, and the ultimate es- 

 tablishment of a closed formation. The dominant plants are grasses; 

 the dominant animals are largely grass-eaters, such as locusts and 

 other phytophagous insects, rodents, etc., with a few of the animals 

 which prey upon these. The associations in the prairie formation 

 are three : the bunch-grass association, the Panicum pseiidopiibcscens 

 association, and a closed association which represents the culmina- 

 tion of the sand prairie, and may tentatively be called the black-soil 

 transition association. 



THE BUNCH-GRASS ASSOCIATION 



The bunch-grass association, being better represented in the sand 

 prairie than the other associations, has been more carefully studied. 



The soil of the bunch-grass association is sand, mixed with a 

 little humus. The association is open, usually about twenty or thirty 

 per cent, of the surface being exposed. The patches of bare sand 

 are dry at the surface, but are not greatly subject to wind action. 

 The topography is usually undulating, the elevations having the as- 

 pect of stabilized dunes, which, in fact, thev almost invariablv are 



(PI. II, Figs. 1,2). 



The dominant plants of this association are the bunch-grasses. 

 which form dense tufts or bunches, in which the dead leaves of the 

 year before remain. The bunches are separated by patches of bare 

 sand. The general appearance of the association depends upon that 

 of the species of bunch-grass which happen to be abundant. The 

 important bunch-grass species are Koclcria cristata (Linn.), forming 



