252 



THE NORTH AMERICAN GRASSLAND 



standing on a small rise of the plain on an August morning might well 

 have seen a large herd of bison grazing to the right, and a smaller 

 herd of antelope to the left, while nearer at hand a coyote or wolf 

 would be seen slipping away to its den. Even today, as one walks 

 about, a long-eared jack rabbit bounds up from behind rock or forb 

 and gallops away, often starting others as it goes. Birds such as the 

 horned lark, lark bunting, Sprague's pipit, and the lark sparrow fly 

 past, singing on the wing. The bee flies and robber flies are unusually 

 conspicuous in flight, and grasshoppers are everywhere in evidence. 

 Such prospects, except for the bison and pronghorn, came into the 

 experience of the authors 30 or more years ago and stand in sharp 

 contrast to the limited outlook in primeval forest. 



Life Forms and Life Habits. The distinctive life form of the 

 prairie is the perennial grass, and to such a degree that an abundance 

 of annuals is an all but infallible index of disturbance. In exclosures, 

 annual grasses have been found to disappear steadily under the com- 

 petition of perennial ones, at least up to the time when the accumula- 

 tion of dry shoots becomes a handicap, and this has been confirmed 

 by the outcome of competition cultures. Moreover, the grass form is 

 to be understood in the ecological and not the taxonomic sense. In 

 their community and habitat relations, such sedges as Carex filiformis 

 and stenophylla are short grasses in effect, and a number of other 

 sedges and of rushes play the role of grasses locally (cf. Weaver and 

 Fitzpatrick, 1934). 



As indicated earlier, life habit in animals corresponds in physiog- 

 nomic value to life form in plants; it is expressed by the terms cur- 

 sorial, subterranean, arboreal, etc. The life-habit ratios of different 



TABLE 10 



Number of Common Species Using Different Portions of the Habitat in 



Breeding, Expressed as Percentages of the Total Number of Species 



* Exclusive of bats. 



