572 



THE COMMUNITY 



munity is also, as a rule, exposed to 

 physiographic change. In combination, 

 these physical and biotic influences produce 

 succession, or succession may take place as 

 a result of physical influences alone. 



Two types of succession take place in a 



speak broadly of two general types. (I) 

 the flowing water sere, and (2) the stand- 

 ing water sere. Both may be known col- 

 lectively as the hydrosere, and their suc- 

 cession spoken of as a hydrarch succession 

 (see also pp. 154-157). 



DISTRIBUTION OF FISHES 



Fig. 209. Serai succession of fishes in the pond-water lily-cattail marsh sere in northern In- 

 diana. Numerals refer to ponds by number, in a series of about 100 ponds, diflfering principally 

 in age, the youngest ( pond 1 ) being nearest to, and the oldest farthest from. Lake Michigan. 

 ( Adapted after Shelford, from Pearse. ) 



ULMUS ^ TILIA- 

 QUERCUS 

 CONSOCIES 



Fig. 210. Probable succession and development in the Fox Lake area of northeastern Illinois, 

 as suggested by index species of plants. ( After Beecher. ) 



given biome under natural conditions. 

 Through time, many serai stages are con- 

 trolled by local conditions primarily, rather 

 than by the prevailing cUmatic conditions. 

 Such sequences are termed edaphic. Two 

 powerful edaphic influences are soil and 

 water. As for aquatic sequences, we may 



Thus within the deciduous forest biome 

 there is the succession that takes place in 

 stream communities (Shelford, 1911). As 

 a stream increases in age, it usually in- 

 creases in length, and there is a consequent 

 increase in its drainage fan (Fig. 30); its 

 species of pioneer fishes hold their relative 



