EQUILIBRIUM 71 
decrease of the former (see chap. i, p. 15), but would probably decrease 
also because of the falling-off of their main article of diet. We may 
thus reasonably assume that the black bass would recover its numbers 
because of the decrease of pickerel and bullheads, the enemies of its 
young. A further study of the diagrams shows that a balance between 
the numbers of the various groups of the community would soon result. 
A B 
DIAGRAM 4 DIAGRAM 5 
DracGram 4.—Showing the life histories of the animals of the pond community 
in the form of circles. The heavy, vertical, black lines represent the animals which are 
dependent upon the most elementary food substances. A represents dead animal 
matter; B, the protozoa, rotifers, and Entomostraca, the smallest animal food. The 
black lines come into contact with different numbers of life cycles, but are indirectly 
connected with all so that any change in the position or rate of movement (meaning 
number or rate of reproduction and growth) of the rod must effect the entire com- 
munity; compare with Diagram 3. 
DriAGRAM 5.—Showing the food relations in the brook community. A repre- 
sents algae which grow upon the stones. B represents the floating animal bodies and 
other organic matter. The latter are of small importance because of their small 
number and the swift current. : 
Under other circumstances, such as the extinction of the black bass, the 
resulting condition would be entirely different from the original one, 
but a balance between supply and demand would nevertheless finally 
be established. The community is said to have equilibrated when such a 
condition is reached; that is, a new equilibrium is established which 
may or may not be like the old. 
