ECOLOGICAL SUCCESSION. 65 



ties of study are, 5^4, at Sawyer, Mich., on sand, 56", at \Vood- 

 ville, Ind., now destroyed, $F, at Sawyer, Mich., and $G, at 

 Otis, Ind., on clay 



III. PRESENTATION OF DATA. 



We will begin with the animals of the earliest forest stage and 

 proceed to those of the latest. For purposes of comparison 

 animals must be divided into groups with comparable habitat 

 relations. Warming's ('09, p. 138) division into strata may be 

 employed (see Dahl, '08, p. n). In any locality we note that 

 there are several levels which may be occupied by animals. 

 Some animals live below the surface of the ground and consti- 

 tute the Subterranean stratum. Others live at the surface of 

 the ground and constitute the Ground stratum. Animals in- 

 habiting the herbaceous vegetation, and low shrubs, etc., 

 make up the Field stratum. Those living on the shrubs and 

 young trees make up the Shrub stratum, and those on the 

 trees, the Tree strata. Such a division is essential to any 

 comparison of the animals of different forests, steppes, etc. The 

 ground stratum of one cannot well be compared with the field 

 stratum of another; like strata must be compared. 



Many animals invade several strata in connection with their 

 various activities. They should, however, be classed primarily 

 in the stratum in which they breed and secondarily in the stratum 

 or strata in which they feed or forage. The breeding activities 

 are of especial importance to the animals in question, while the 

 feeding and foraging influence other animals. The study of 

 the lower strata of the forest presents no difficulties. The tree 

 stratum however is usually far enough above the ground to 

 make observation difficult. The data at hand are rather incom- 

 plete at this point and accordingly the discussion is confined to 

 the lower strata. 



Tables I. and II. and the lists following them show the distribu- 

 tion of about 200 species of animals in the forest stages. These 

 tables and lists include chiefly animals that have been encountered 

 in these situations often during several seasons. Where collec- 

 tions are known not to have been representative, they are 

 omitted. For example most of the Diptera collected were pre- 



