254 THE NORTH AMERICAN GRASSLAND 



ousness of the prairie chicken in contrast to the sohtary habit of its 

 relative, the ruffed grouse. 



Modern ecology has appeared so late as to require reconstruction 

 to evaluate properly the various species of the grassland, either plant 

 or animal, as well as those of other communities dominated by man. 

 This is especially true of the animals, as few relicts of this biome have 

 remained entirely unmodified in this respect. The habits and habitat 

 relations of each species must be known to interpret its past and pres- 

 ent range. The gradual removal of the generally continuous forest 

 cover of the eastern states and southern Canada for nearly three cen- 

 turies gave abundant time for birds, insects, and other animals of the 

 forest edge, swamp, and moist meadows to invade the eastern United 

 States. Again, the planting of trees in the prairie from 1860 to 1938 

 has afforded opportunity for forest-edge species to extend westward. 

 This period undoubtedly represents marked expansion of the popula- 

 tions of those animals favored by man directly or indirectly. 



The community and habitat relations of an animal species can 

 usually be ascertained from good field data, but unfortunately, in the 

 early period of scientific exploration previous to 1890, the ecological 

 results of expeditions were commonly lost by the process of segrega- 

 tion of collections to specialists and by the practice of stressing the 

 description of the species only. In the mid period (1890-1910), taxo- 

 nomic monographs and other papers gave little habitat data in connec- 

 tion with the life-zone work, although any life zone includes many 

 unlike habitats. IVIoreover, all the drier grasslands were confused 

 with desert, and even in typical grass communities few or no grasses 

 were listed as habitat or zone indicators, attention being focused upon 

 the conspicuous woody and succulent forms. With the rise of the eco- 

 logical viewpoint, natural history works of definite ecological value 

 began to appear; those of Seton (1929), the excellent state treatments 

 by Bailey (1931), Hebard (1925-1931), and others are noteworthy. 



Climate. In harmony with its wide extent, the climatic relations 

 of the prairie exhibit a greater range than those of any other climax 

 on the continent. On the east its boundary lies close to the isohyet 

 of 40 inches from Texas to Indiana, while on the northeast it drops 

 from that of 35 to 25 inches in correspondence with lessened evapora- 

 tion. The extremes of temperature are even more striking, varying 

 from a frost-free season of but three or four months in Canada to one 

 of practically an entire year in southern Texas. The chief explana- 

 tion of this seeming anomaly is to be found for both plants and ani- 

 mals in the evasion of temperature extremes by virtue of the habit of 

 perennation on the one hand and that of burrowing on the other (cf. 



