These in turn serve as food for other predatory aquatics — some of them are also eaten 

 up by fish — and these again constitute the natural foodstuffs of fishes. We have therefore 

 the complete cycle of: 



Original, mineral (inorganic) nutrients 

 Original producers (the plants) 

 Intermediate consumers (aquatics) 

 Ultimate consumers (fish) 



In addition to these v/e have further the reducing components of the cycle (not charted 

 in our sketch for reasons of clarity) which conclude the process and bring back to their 

 points of origin, all decayed organic substances. V>e may regard them also as consumers. 



These reducers are chiefly bacteria, especially those leading to fermentation and 

 putrefaction. It is through their respiratory labor— either aerobic or anaerobic, i.e., 

 v;ith or without oxygen consumption — that they gradually "mineralize" the reducible organic 

 substance matter of plants and live organisms (carbohydrates, fat and protein) back into 

 original, inorganic matter, therefore bringing to a close the T*iole catabolic cycle. 



'iVe have a perfect example of this cycle in the lake , which forms a unit and entity all 

 in itself. V.'e find there three well defined biological communities, to wit: Shore region, 

 bottom (floor) region, and free-water region. 



Shore region and upper (lighted) free-water region fom creative, independent biological 

 areas, where producers and consumers intermingle. 



The bottom region, and also the lower (deeper) free-water region, are nonproductive 

 areas, dependent upon the former for sustenance. 



In contrast to the lake, and from the viewpoint of the above classifications, the pond 

 is an out and out independent, biological community. 



The reason for it lies in the fact that a pond is normally very shallow, so that 

 light will penetrate to its very bottom, thus allovdng for the development of plant life. 

 In this respect the pond resembles the shallow shore regions of the lake, but not only upon 

 its shores, like the former, but in its whole area. Life conditions in the pond therefore 

 resembles and are as varied as those in the shore regions of the lake. 



It would be quite insufficient though to speak of "shore plants" and "shore life" in 

 the pond as is so often done. 



In the pond also, we have to deal with three distinct biological communities, distinct 

 from each other, but constantly reaching and cutting into each other's sphere. 



Investigations by Pauly in Sachsenhausen have definitely established the fact that 

 also in free-viater regions of the pond, and between and within its flora, genuine plankton 

 is to be found. That is, this form of small animal life which aimlessly drifts and swims 

 around, devoid of will and oblivious to direction. 



A second biological community consists of ttie higher submerged flora and of the "cover- 

 algae", growing upon stones, upon poles and at the bottom and provides foodstuff for the 

 numerous species of aquatic and of micro-organisms, and of which they are especially fond 

 on account of the tender tissues. 



All organic life found within the plant profusion or upon the "coverings" at the 

 bottom of the pond is spoken of as vegetation animals. They will occasionally, stray into 

 the fresh-water regions but will always return to their base, which offers them sustenance. 



The third and quite distinct biological community consists of bottom life, that is, 

 the world of aquatic life dwelling upon the floor of the pond. Contrary to certain beliefs, 

 this form of life is not only to be found in such spots which are free from vegetation but 

 may be found, quite plentifully, near the roots of plants if other conditions of life are 

 favorable. This is true especially of Chironomus plumosus. the most characteristic form of 

 all bottom life organisms. 



P-7IJ09 



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