34 VICTOR E. SHELFORD. 



bring about a better unification and organi/ation of biological 

 science as a whole. 



V. SUMMARY OF TENTATIVE "CONCLUSIONS. 



1. The quantity of bacteria, plankton, vegetation and large- 

 animals increases as a pond grows older. 



2. Terrigenous bottom and oxygen content decrease as a pond 

 grows older. 



3. The distribution and succession of fish are not determined 

 by kind of food; kind of food eaten is determined by the availa- 

 bility in localities suitable in other respects. 



4. Fish are not necessarily present where food is quantitatively 

 greatest. 



5. The food and game fishes here considered are closely as- 

 sociated with their breeding conditions to the neglect of depth 

 of water, food, etc. 



6. Low oxygen content on breeding grounds is a sufficient 

 cause for their absence from the older ponds. 



7. Conditions outside the breeding season are probably of 

 secondary importance in the success of fish in a given locality. 



8. The food interests and breeding interests of the food and 

 game fish here considered are decidedly antagonistic. The for- 

 mer continually encroaches upon the latter. 



9. Successful fish culture in ponds and small lakes depends 

 upon the maintenance of balance between the breeding and 

 feeding conditions. 



10. Animal succession in ponds is due to an unused increment 

 of excretory and decomposition materials which causes an in- 

 crease in vegetation, a decrease in Oo, on the bottom and a general 

 change in surrounding conditions, all primarily affecting breeding. 



i i . Succession of species is the result of stability of the mores 

 of species concerned; when mores are flexible species do not 

 succeed one another but continue with changes in behavior and 

 physiological characters. 



HILL ZOOLOGICAL LABORATORIES, 

 UNIVERSITY OF CHICAGO, 

 August i, 191 1. 



