XIII -THE FIRST FOOD OF THE COMMON WHITEFISH. 



{Coregonus clupeiforinis, Mitch.) 



By S. A. Forbes. 



In a very large lake the couditions of life are remarkably uniform. 

 The volume of water remains, of course, constant from season to season 

 and from year to year, and the extremes of summer heat and winter 

 cold have but a moderate effect upon the temperature of the lake an a 

 whole. Consequently both plant and animal life exhibit there a regu- 

 larity and stability which are in remarkable contrast to their fluctua- 

 tions in smaller bodies of water and on the surrounding laud. Il^ot 

 only do the relative numbers of individuals in the various species re- 

 main about the same, but the absolute number of each must necessarily 

 change but little, as a rule. 



Such a state of affairs is eminently favorable to an exact and econom- 

 ical balance of supplj" and demand, of income and expenditure, of mul- 

 tiplication and destruction, among the inhabitants of the lake. Here 

 every species of animal, whether predaceous or vegetarian, must find, 

 in the sur])lus products of growth and reproduction among the species 

 upon which it depends for food, a far more constant and unvarying 

 supply for its needs than elsewhere ; and the species fed upon must be 

 subject to a far more regular drain upon their surplus numbers or un- 

 essential structures. Where there is little fluctuation there is little 

 waste. 



A system of life like this, running on with relatively even tenor for 

 centuiies, must of course be much lessJJexible than one where wide and 

 violent fluctuation and continual readjustment are the rule; and a spe- 

 cies in any way deeply affected will here have within itself far less re- 

 cuperative power than one which has been forced again and again — 

 each year, perhaps — to rally against the most destructive attacks as the 

 price of its continued existence. Disturbances of the natural balance 

 of life, of the primitive and spontaneous system of reactions by which 

 the different groups of organisms are related, will therefore be unusu- 

 ally serious and lasting; and where such disturbances result from hu- 

 man interference, as by the yearly capture of large numbers of any 

 important fish, it is especially desirable that artificial means of com- 

 pensation be taken to restore the disturbed balance as nearly as i30ssi- 

 ble. Excessive loss will be made good by natural reactions far mor^ 



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