168 ARTHUR G. VESTAL. 



The occurrence of a grasshopper species, or of several species, 

 in two habitats or associations does not mean that these furnish 

 similar environmental complexes for animals. It means simply 

 that certain environmental conditions necessary for these par- 

 ticular species are included among the conditions provided by 

 these habitats. Thus in the Douglas Lake region, Melanoplus 

 islandicus is found in beech-maple forest and in the cedar-bog 

 forest. These two associations are radically different in many 

 respects, as habitats for animals. The entire range of conditions 

 presented within the area of an association, particularly if it be 

 extensive, is likely to be considerably more inclusive than the 

 range of conditions required by many animal species. Taxo- 

 nomic groups of animals which are affected more particularly by 

 conditions differing in the two habitats, will be represented 

 differently in them. It follows that very little reliance can be 

 placed on comparisons of habitats on the basis of the study of a 

 taxonomic group, such as grasshoppers, except in respect of the 

 particular conditions critical to the species of this group. Com- 

 parisons of the entire animal communities of the two habitats 

 would not be subject to this limitation, since nearly all of the 

 environmental conditions within the two habitats would come 

 into consideration. 



Within any one association the animal species may be dis- 

 tributed generally throughout its area, as Melanoplus angusti- 

 pennis in the bracken-blueberry growth; in certain instances it 

 may be restricted to a part of the area characterized by a slight 

 environmental difference; or it may occur in scattered parts of 

 the association, characterized by scattered local differences, as 

 Scirtetica marmorata in the lichen-covered patches within the 

 bracken-blueberry growth. 



The Animal Environment. In addition to the physical and 

 vegetational influences upon the animal species, that of its animal 

 environment must also be recognized. Direct effects of the 

 animal-environment upon the animal species are probably 

 greater than the indirect effects produced by modification of 

 physical and vegetational environments. Among these latter 

 more general effects of the animal community are the accumula- 

 tion of organic remains, and particularly the effects of phy- 



