286 



CIVIC BIOLOGY 



CO 

 O 



an 

 o 



1 



SPECIES 



TIME — 



UNDER 

 NATURAL 

 CONDITIONS 



UNDER 



HUMAN 



CONTROL 



Attack 

 by Ma7\ 



Adults. 

 Lohsierlings 



\Na tural'Enem iesy 





^ih 



Fig. 



TOO 



loo. 



Diagram expressing Brooks's law of the extermination of a species 

 by man as applied to tlie lobster problem 



The species is shown flowing along from an indefinite past nnder natural condi- 

 tions, with minor fluctuations, hut maintaining a practically constant population, 

 ha^^ng adjusted itself to its natural enemies hy developing great fecundity, as 

 seen in the wide stream of eggs and larva;, most of which are taken in the larval 

 stage hy natural enemies. At the large arrow civilized man attacks the slender 

 stream of adult lobsters which nature has selected to keep up the supply of eggs. 

 This strikes the species as a "catastrophe." IMan's attack is unlike that of all 

 other enemies. Instincts of self-preservation, thickness of shell, and large size, 

 which made the adult lobsters almost immune from attacks by other enemies, 

 all are of no avail. Although man takes but a small number of adults, the bal- 

 ance is disturbed, fewer eggs are produced, natural enemies crowd and tend to 

 take a larger proportion, and the species swiftly approaches extermination. Even 

 if man ceases his attack when the numbers have become reduced so as to render 

 their further pursuit unprofitable, natui-al enemies may kill off the stragglers, and 

 before we realize what has happened, the race is extinct. If we did shut off all 

 the streams of young and adults at the jioint of the large arrow, we should have 

 a picture of the extermination of the lobster. Under human control, if even a 

 few adult breeders are left, man can increase the number to any desired amount; 

 he can lift the eggs and young above the reach of natural enemies, or crowd 

 them down, or both, and so increase the species to the limits of room or of food 

 supply. This is what we hope is now being done, and we shall watch the future 

 curves of increase in the expectation that the price of lobsters may begin to 

 decline toward reasonable limits. This diagram is applicable to any species ex- 

 terminated or in danger of extermination by man — passenger j^igeon, dodo, great 

 auk, and many other species now lost to the world 



286 



