GRASSHOPPERS IX RELATION TO PLANT ASSOCIATIONS. l6l 



habitat in which the species is more frequent and abundant is of 

 considerable extent within the region, as in climatic associations, 

 soil conditions, or conditions for egg-laying, would be either 

 uniform throughout the area of the habitat, or else suitable small 

 spots would be scattered about within the area. There would 

 then be no necessity for the females to migrate to a different 

 habitat for oviposition. Thus most of the grasshoppers found 

 in the aspen association would be able to lay eggs within its 

 area, and the nymphs would find food and other necessary condi- 

 tions in the same place as do the adults. In the beech-maple or 

 cedar-bog forests, which individuals of Melanoplus islandicus 

 probably rarely leave, suitable egg-laying sites, in this case wood 

 as found in stumps or logs, are scattered about over the forest 

 floor. It thus appears probable, in the extensive habitats 

 provided in terrestrial climatic plant associations, that the corre- 

 spondence between the conditions required for breeding and 

 the conditions required for feeding and other ordinary activities, 

 may be quite general. Conditions for egg-laying among insects, 

 for example, may still be more restricted than conditions required 

 for other activities, but the local variability of environmental 

 conditions within the area of the plant association is sufficiently 

 wide, usually, to include the more restricted conditions necessary 

 for egg-laying, or whatever the most narrowly limited activity 

 happens to be. If what is true in the case of grasshoppers is true 

 in a large number of terrestrial animals, as seems likely, this 

 means that the limits of the climatic plant association need not 

 be passed, ordinarily, by a large number of the animal species, 

 since all the necessary conditions are supplied within its area. 

 The animal community of the area may be thus, in large measure, 

 self-contained, and coextensive with the plant community. 



In local habitats, on the other hand, which are usually re- 

 stricted in extent and consequently likely to present less varia- 

 bility of environmental conditions within the area, it is less likely 

 that all the conditions necessary for the animal species will be 

 supplied within the area. The number of animal species which 

 can find all the necessary conditions for existence within the area 

 will be comparatively small; thus many of the species will be 

 obliged to perform certain of their activities in other habitats. 



