The Prodiiciivily of Fish Food in Oneida Lake 149 



quantum of life which enters into a certain number of indi- 

 viduals, and which, as does all life, gains permanence by means 

 of transmission." 



Mobius ('83, p. y2Tf) recognizes the fact that this biocoenosis 

 is subject to change either by external environmental factors or 

 by the increase, decrease, or elimination of one or more species 

 forming the community. An interesting example is cited of 

 the rich oyster beds of Cancale, Rochefort, Marennes, and 

 Oleron, in France, in which the cockles (Cardiiim edide) and 

 edible mussels {Myiihis edidis) replaced the oysters after the 

 latter had been harvested for market. The oyster beds could 

 be restocked only by removing the cockles and mussels to make 

 room for fresh young oysters " because the ground is alread)' 

 occupied and the food all appropriated ". Mobius furthei' 

 remarks that " space and food are necessary as the first requi- 

 sites of every social community, even in the great seas ", and 

 this is equally true of a fresh water lake or pond. 



