1 62 ARTHUR G. VESTAL. 



Furthermore, environmental conditions in local habitats are 

 likely to be the extreme, rather than the mean, conditions within 

 the region. Thus sedge mar^h habitats in the Douglas Lake 

 region have submerged or very wet soil; in the latter case, the 

 growth may be so dense as to leave no exposed soil. These are 

 extreme conditions for terrestrial habitats. The only grass- 

 hopper of the region which was seen in such situations is the 

 ectophytic Stenobotlints curtipennis. It is probable that this 

 species deposits its eggs in higher and drier soil. Unlike most 

 of the grasshoppers, its ordinary activities can be carried on in a 

 very humid environment, and the presence of exposed soil is 

 not necessary. The conditions necessary for breeding, however, 

 do not correspond with the extreme condition of wet soil, and 

 must be obtained outside the area of the extreme habitat. The 

 local habitat is less likely to be self-contained than the extensive 

 or climatic habitat. 



Difficulties Arising from Habitat Complications. The habitat 

 relations of animals sometimes are much less evident at the 

 tension zone between two contiguous habitats, and there is the 

 further complication that habitats are sometimes distinguished 

 with difficulty. Boundaries will be invaded by animals of both 

 habitats. The tension zone is much wider, and the confusion 

 greater, between two rather similar habitats. As Shull points 

 out ('n : 221), the determination of habitat relations is difficult 

 in regions where the habitats are small in area and much inter- 

 mingled. The tension zone presents one great advantage in 

 that it allows determination of which species of one habitat 

 range farthest and most frequently into the adjoining habitat. 

 A graded series of species can be determined, which expresses the 

 resultant of different factors entering into habitat selection of 

 the different species. 



Unstable habitats are frequently indicated by the presence of 

 mixed plant associations. These contain representatives from 

 two or more plant communities. Thus near the beach of Douglas 

 Lake, the bracken-blueberry growth is mixed with bearberry and 

 juniper heaths, a few small clumps of beach-grasses, in certain 

 spots, and in others by local growths of ruderal bluegrass. In 

 such mixed areas the animal assemblage is not of the constant 

 character seen in more uniform growths. 



