ECOLOGICAL SUCCESSION. 89 



A. Pioneer Communities. 



The communities of the cottomvood, pine and black oak stages 

 may be designated as pioneer because of the presence of bare 

 mineral soil. 



1. Subterranean and Ground Strata. (a) The cottonwood com- 

 munity is characterized by animals which breed and spend the 

 dark and cloudy days chiefly below the surface of the sand. 

 They are very largely diurnal and predatory, are exceedingly 

 swift and wary. The burrowing spider (Geolycosa pikei) is one 

 of the few nocturnal animals. 



(b) The pine community is characterized by similar mores, 

 but is to be distinguished from the preceding by the presence 

 of many animals which prefer sand that is less shifting and 

 which is slightly darkened by humus (Shelford, '07). Animals 

 requiring "cover," such as the lizard, the blue racer, a few 

 ground squirrels, etc., give character because of their absence 

 from earlier and later communities. 



(c) The black oak community represents the climax of diversity 

 of the subterranean and ground strata. The bare sand mores 

 continue in the open spaces, which we have designated as tran- 

 sition areas. Leaf cutters are now present while among the 

 burrowers, the root borers (Prionids and Lucanids) work on the 

 roots of the decaying trees. The behavior differences between 

 this and the preceding communities are differences of detail which, 

 for the making of deductions, would require much careful study. 



2. Field and Shrub Strata. The field and shrub strata of the 

 cottonwood, pine and oak communities are less easily char- 

 acterized. The cottonwoods of the beach are far less commonly 

 infested with aphid galls than are trees of the same species 

 growing in less exposed situations. Furthermore we have never 

 found any of the lepidopterous larvae such as Basilarchia archip- 

 pus near the beach. Animals living exposed upon the trees are 

 few in number. The same general conditions obtain on and 

 among the pines but spiders are more numerous. On the black 

 oak the number of phytophaga is increased and the number of 

 galls appears to be greater than in the later stages; the inhabi- 

 tants of the herbaceous vegetation are chiefly those found in 



