394 ENTOMOLOGY 



the subterranean- ground stratum, the field stratum (zone of the tops 

 of the herbaceous vegetation), the shrub stratum (zone of the tops of 

 the dominant shrubs), the lower tree stratum (zone of the shaded branches 

 of the trees), and the upper tree stratum. A given animal is classified 

 primarily with the stratum in which it breeds, as being most impor- 

 tant to it, and secondarily with the stratum in which it feeds, etc., as in 

 many cases most important to other animals. The migration of ani- 

 mals from one stratum to another makes the division lines difficult to 

 draw in some cases. Still, the recognition of strata is essential but a 

 rigid classification undesirable. Consocies boring into the wood of 

 living trees probably should be considered as consocies relatively 

 independent of stratification phenomena. 



"Associations are groups of strata uniform over a considerable area. 

 The majority of mores, consocies, and strata are different in different 

 associations. A minority of strata may be similar. The term is 

 applied in particular to stages of formation development of this ranking. 

 The unity of associations is dependent upon the migration of the 

 same individual and the same mores from one stratum to another at 

 different times of day or at different periods of their life histories. 

 Migration is far more frequent from stratum to stratum than from one 

 association to another. 



"Formations are groups of physiologically similar associations. 

 Formations differ from one another in all strata, no two being closely 

 similar. The number of species common to two formations is usually 

 small (e.g., 5 per cent.). Migrations of individuals from one formation 

 to another are relatively rare." (Shelf ord.) 



VI. EXAMPLES OF INSECT COMMUNITIES 



The article by A. G. Vestal, from which the following extracts 

 taken, though limited to a single group of insects, the grasshoppers, 

 is a good example of how entomological field observations may be 

 organized on an ecological basis. The observations were made at 

 Douglas Lake, Michigan. 



COMMUNITY-RELATIONS OF GRASSHOPPERS 



Northeastern Conifer Formation. Thuja Association. Cedar and 

 peat bog. Melanoplus islandicus the only species. 



Aspen Association. In treeless parts, M. angustipennis is the 

 common species. M. luridus is found sparingly in scattered aspen 



