GRASSHOPPERS IN RELATION TO PLANT ASSOCIATIONS. 167 



Vertical Distribution. The distribution of terrestrial animals 

 in space is both vertical and horizontal (Shelford, '126). Most of 

 the grasshoppers of the Douglas Lake region belong to the ground 

 and field (herbaceous) strata, as do the Acridiidce in general. 

 With the exception of the forest species which oviposit in wood, 

 the eggs are laid in the soil. Most of the species require bare soil, 

 and many of their activities take place directly upon the surface. 

 Stenobothrus is more commonly seen upon the plants, and certain 

 species of Melanoplus live upon the plants part of the time. 

 Podisma glacialis variegata is a shrub-inhabiting species. Grass- 

 hoppers are in general typical animals of the ground stratum. 

 Other families of Orthoptera are more typical of other strata. 



Horizontal Distribution. Within a region an animal species 

 will select habitats or associations in which conditions of the 

 optimum environment are most closely approximated. The 

 table on p. 153 indicates that no two grasshopper species of the 

 Douglas Lake region select the same set of environmental condi- 

 tions. Certain of the species are similar in distribution, but 

 none are identical. They replace one another in different 

 habitats, with some overlap, and can be arranged in series 

 according to gradients of environmental factors (Fig. I, p. 156). 



Although a single species may be found in more than one 

 association, it is not equally abundant nor equally regular of 

 occurrence in these associations. Certain of the grasshopper 

 species are typical of only one association, as Melanoplus fasciatus 

 in closed aspen forest. Melanoplus atlanis, the most generally dis- 

 tributed species, though abundant in five habitats, is most abun- 

 dant in ruderal grassland, and very typical in such situations. 

 Other grasshoppers are more characteristic of the other four 

 associations in which Melanoplus atlanis is abundant. 



The various habitats in which a particular species may be 

 found happen to be more or less similar in physical and vegeta- 

 tional conditions. Data in the table on p. 153 indicate that 

 those associations in which a grasshopper is found in common 

 may agree only in containing certain or all of the conditions 

 necessary for that species, and that there need be no successional 

 or geographic relationships between the associations, nor is it a 

 matter of concern whether the associations be native or ruderal, 

 extensive or local. 



