ARTHUR G. VESTAL. 



grasshoppers within a region is the area marked off by the plant 

 association, in which there is a general and usually recognizable 

 uniformity of vegetation and of physical conditions. 



A species is to be assigned to a habitat if its occurrence in that 

 habitat is a matter of regularity. In general, the animal species 

 is seldom confined to a single habitat within a region. The 

 determination of the more typical habitats selected by a par- 

 ticular species involves estimation of relative numbers, and 

 presents certain difficulties, which are discussed below r . In a 

 regional study of a group of animals taxonomically related, or of 

 all the animals of the region, there are certain other difficulties 

 which obscure the definiteness of habitat relations. 



Variation in Range of Habitats in Different Species. The 

 range of toleration of environmental conditions varies wddely 

 among different species of a taxonomic group, and accordingly 

 we find certain animals restricted to one or several similar 

 habitats, while others range over many and different habitats 

 with apparently little discrimination. Melanoplus atJanis, for 

 example, occurs regularly in meadows, in dry open grassland, and 

 in open forest. It is a species which can endure widely varying 

 conditions. Upon examination, it is found that it is very much 

 more numerous in certain habitats than in others, and that there 

 are certain habitats in which it occurs only accidentally or not 

 at all. In the Douglas Lake region, it was never seen in cassandra 

 bogs, in bog or ravine forests, in closed aspen forest, and only 

 infrequently or accidentally in closed hardwood forest. There 

 is, then, a selection of habitats, and the local distribution of even 

 . the most generally distributed forms is far from indiscriminate. 

 Habitat- Distribution as Affected by Motility of Animals. The 

 habitat relations of plants are more evident than those of animals 

 because the plant individuals are non-motile, while animal 

 individuals can move about, and it is not to be supposed that they 

 will necessarily stay within a single area of uniform conditions. 

 They continually stray beyond the limits of conditions necessary 

 for all or part of their activities. Among the grasshoppers, 

 certain are much more motile than others, particularly the long- 

 winged and active (Edipodince. These grasshoppers at times fly 

 high and to considerable distances, and may be seen to traverse 



