GRASSHOPPERS IN RELATION TO PLANT ASSOCIATIONS. 169 



tophagous animals upon vegetation. It is probable that animal 

 environmental influences are greater than is commonly supposed, 

 but that ordinarily they play a subordinate part as compared 

 with physical and vegetational influences (cf. Shelf ord, 'i2a: 94). 

 The grasshopper species is not only affected by the animal 

 environment, but is itself a part of it. So far as the relations of 

 the grasshoppers to the association and with other species is 

 concerned, about all that is known, in general, is that they are 

 among the most important of the plant-eating animals of grass- 

 land associations, in which some of them are dominant species; 

 and that they form the principal food supply for a comparatively 

 large number of predaceous and parasitic enemies. It is not 

 known to what extent different grasshopper species compete 

 with one another. Differences in habitat and in time of activity 

 may indicate removal of competition among certain species. 



Successional Relations. 



The successional relations of the Douglas Lake associations 

 have been discussed by Gates ('13: 48), and a diagram illustrat- 

 ing the successions is included. The work on the grasshoppers 

 has not covered so wide an area, consequently many of Gates' 

 associations are not well represented. Fig. I, on p. 156, will 

 serve to illustrate successional relations of the associations in 

 which grasshoppers were taken, and the changes in grasshopper 

 species may also be seen, as one plant association is replaced by 

 another. Initial stages in dry soil are shown at the lower left- 

 hand part of the diagram; initial stages in wet habitats at the 

 lower right. The two series converge at the top of the curve, in 

 the climax beech-maple forest. The ordinary course of succes- 

 sion from marsh associations is toward bog forest; from beach 

 grass into pine forest. These successions are not shown in the 

 diagram. The aspen association is the result of secondary succes- 

 sion from pine forest, which is no longer well represented in the 

 immediate region. Grassland associations between beach-grass 

 and wet meadows are represented only by ruderal growths ; which 

 have originated mostly by secondary succession. Closed grass- 

 land is not represented, for invasion by forest occurs before it 

 can develop. 



