SUCCESSION OF COMMUNITIES aba 0 TE 
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 
—BASE-oF— puuFF___- ——— 
LAKE MICHIGAN. 
Fic. 67.—Diagrammatic arrangement of the North Shore streams. Thestreams 
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 
