CHAPTER VIII 



ANIMAL COMMUNITIES OF PONDS 



I. Introduction 



Ponds are fascinating to all, and do not lack interest from the scien- 

 tific point of view. They are of especial interest to those familiar with 

 the laboratory study of zoology. The common animals of the laboratory 

 are pond animals, because pond animals are forms that will live in 

 stagnant water. The common aquarium fishes are all pond fishes, as 

 the brook forms die quickly if they are not supplied with running water. 

 The frog, so much studied, is a pond form. The conditions in ponds are 

 different from those in lakes and streams, because currents are not strong 

 nor particularly important. The water doubtless piles up at one side 

 or end of a pond during strong winds, and a complete circulation is 

 effected, but this is not important. All of the conditions of lakes are 

 duplicated in ponds, but on a smaller scale. One of the chief differences 

 between ponds and lakes is the vegetation. Ponds are usually very 

 largely captured by vegetation which is very much like that in the bays 

 of lakes. Succession of plants in ponds is similar to that in lakes; the 

 age of a pond is therefore a matter of first importance. The bottom 

 materials are of most importance at the beginning (6, 112). The bottom 

 materials in the ponds of the Chicago area are rock, clay, and sand. 

 Rock-bottomed ponds have been but little studied, though there are a 

 number of ponds in abandoned quarries of different ages which would 

 make a good series for investigation. Clay bottom occurs in the moraine 

 area. Nearly all the natural clay-bottomed ponds have reached a stage 

 at which the bottom is not important, but one could no doubt find a 

 good series if he were to make a special study. Sand-bottomed ponds 

 are the commonest of all, and for the purpose of studying the effect of 

 age upon ponds, a series of sandy-bottomed ponds, which differed chiefly 

 in the matter of age, was selected. 



II. Area of Special Study 



The ponds that have been made the subject of special study lie in 

 the sand area at the south end of Lake Michigan, within the corporate 

 limits of the city of Gary, Ind. They may be reached from the stations 

 known as Pine, Clark Junction, and Bufiington (Fig. 84). The locality 



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