SUCCESSION OF COMMUNITIES 



in 



other animals living with them. To illustrate the succession of fish in 

 streams we shall consider succession of fish in the North Shore streams. 



b) Statement of ecological succession. — Succession is a reconstruction. 

 Here it is based on the superposition of all the fish communities (Fig. 67) 

 over the oldest part of the oldest and largest stream. To make this 

 clearer we will state, with the aid of the diagram (Fig. 69), the succession 

 of fish in Bull Creek. This succession will be considered as taking place 



Fig. 67. — Diagrammatic arrangement of the North Shore streams. The streams 

 are mapped to a scale of one mile to the inch, and the maps are placed as closely 

 together as possible in the diagram. The intermediate shore-lines are shown in broken 

 lines which bear no relation to the shore-lines which exist in nature. Toward the top 

 of the diagram is west. Each number on the diagram refers to the pool nearest the 

 source of the stream which contains fish, as follows: 1, the horned dace (Semotilus 

 atromaculatus); 2, the red-bellied dace (Chrosomus erythrogaster); 3, the black-nosed 

 dace (Rhinichthys atronasus); 4, the suckers and minnows; 5, the pickerel and blunt- 

 nosed minnow; 6, the sunfish and bass; 7, the pike, chub-sucker, etc. The bluff 

 referred to is about 60 ft. high. The stippled area is a plain just above the level of the 

 lake (see Table XVIII). 



over the oldest part of the portion of Bull Creek which lies back of the 

 bluff and higher levels of Lake Michigan. This is the point designated 

 as 5. (Table XVIII and Figs. 67 and 69 should be before the reader.) 

 When Bull Creek was at the stage represented by the first stage in 

 our diagram (which is represented by the present Glencoe Brook), its 

 fish, if any were present, were ecologically similar to those now in Glencoe 

 Brook in their relations to all factors except climate. This ecological 

 type is represented by the horned dace alone. As Bull Creek eroded its 



