COMMUNITY SUCCESSION AND DEVELOPMENT 



573 



ecological position by continually shifting 

 their range so as to remain near the stream's 

 source, or sources. Similarly, as the aging 

 stream lowers its bed, loses velocity, and 

 consequently lowers its capacity for carry- 

 ing a load of suspended materials, the lower 

 reaches of the stream, e. g., the oldest por- 

 tions, are occupied by different fish popu- 

 lations (p. 155). 



Still other types of edaphic successions 

 take place in bodies of standing water; for 

 example, in lakes, ponds, marshes, and 

 bogs. 



., BEECH and 

 '-(-■'. 'MAPLE FOREST 



Fig. 211. Diagram of succession and devel- 

 opment from the edaphic pond-marsh sere into 

 either the grassland sere or the forest sere, de- 

 pending upon climatic influences. The three top 

 figures show the accumulation of bottom ma- 

 terials (diagonal hatching) and through time 

 the appearance of submerged and later emerg- 

 ing vegetation vdth accompanying changes in 

 fauna. The two bottom figures suggest climatic 

 alternatives of grassland or forest development. 

 (After Buchsbaum.) 



A well-established classification of lakes, 

 based upon certain aspects of productivity, 

 involves lake succession and development. 

 First, the oligotrophic lakes are poor in food 

 materials, and usually deep, the hypolim- 

 nion is larger than the epilimnion, littoral 

 plants are not abundant, plankton is 

 quantitatively poor, water bloom is rare, 

 and such lakes develop into the second 

 type. The second type of lake in this 

 classification is known as eiitrophic. These 

 are rich in food materials, often shallow, 

 the hypolimnion is smaller than the epilim- 



nion, httoral vegetation is abundant, the 

 plankton is rich, and there is a characteristic 

 water bloom of rapidly reproducing algae. 

 These eutrophic lakes develop into ponds, 

 marshes, and wet meadows. 



The third type, the dystrophic lakes, 

 occur in old mountain ranges, or are as- 

 sociated with bogs. Such lakes have Uttle 

 Httoral vegetation or phytoplankton, water 

 bloom is consequently rare to absent, and 

 there is a great deal of disintegrating 

 humus material, but a scanty benthos. Such 

 lakes develop into peat bogs as a rule. 



In general, ponds, lakes, and marshes, 

 in addition to drainage that may or may not 

 take place through the agency of streams, 

 age from the bottom upward, through 

 building up of the subaqueous stratum. 

 Such communities tend to have an alkahne 

 medium, and the filhng of ponds is illus- 

 trative of the process. 



As the level of the postglacial Lake 

 Chicago fell, to form the present Lake 

 Michigan (Fig. 202), a series of transverse 

 ridges and pond-filled depressions was ex- 

 posed. This pond series was studied by 

 Shelford (1911b, 1911c, 1913) for the suc- 

 cession taking place, from the younger 

 ponds, nearest the lake shore, to the oldest 

 ponds, much farther inland on the old lake 

 bed. Figure 209 illustrates fish succession in 

 younger ponds of this sere. As the ponds 

 aged, pioneer species of plants and animals 

 disappeared and were replaced by others 

 that could tolerate the changed conditions. 

 For example, there was a general decrease 

 in bare bottom, and an increase in vegeta- 

 tion, total food resources, and bottom de- 

 posits with age. This decreased the breed- 

 ing area for pioneer fishes such as black 

 bass and sunfishes, and the maturing ponds 

 held an increasing population of perch, 

 chub sucker, and speckled bullhead. Still 

 later, with the ponds having a thick bot- 

 tom deposit, and with the water becoming 

 choked with floatincr and, later, emergent 

 vegetation, black bullheads became more 

 numerous. It should be emphasized that 

 some species, such as the mud minnow, 

 appeared in the early ponds and continued 

 through most of the sere. Such species may 

 be said to have a high serai adaptability and 

 are of small value as serai indices, because 

 of their range of toleration. In general, it 

 may be postulated that the value of a spe- 

 cies as a serai index is inversely proportional 



