72 AQUATIC CONDITIONS 
The causes of fluctuations of numbers of organisms are numerous. 
Cold winters often destroy aquatic vertebrates. Large rainfall dilutes 
the plankton in streams and carries it away. Too little sunshine causes 
a poor production of the chlorophyll-bearing organisms which are the 
food basis of all the others. High temperature favors denitrification. 
From Diagram 3 and brief discussion above it will be seen that there 
are in a pond community, close interrelations traceable to certain groups 
which are closely dependent upon the more elementary food substances. 
A representation of these relations is given in Diagrams 4 and 5s. 
