DENSITY OF POPULATION AND INSECT SURVIVAL 243 



remainder of their lives under the conditions implied thereby, their 

 average duration of life is reduced in these experiments from the 34 

 or 35 days which it would have been had they stayed in the bottles 

 with an initial density 35, to 22.83+0.19. This result shows that 



K Density 35 Throughout 

 X i^/ings Not Clipped 



''rs Density 35 Throughout 

 \Aj'Vings Clipped 



Age in Days 



Fig. 20. — Showing survival curves starting with 1,000 individuals of Drosophila 

 at 16 days of age which had been subjected to different densities of population up to 

 that time. (From Pearl, Miner, and Parker, 1927.) 



crowding produces a heavy increase in mortality even though it 

 occurs as late as 16 days of age. 



"Flies which have lived the first 15 days of their lives under the 

 conditions implied by an initial density of 200, and then at the age 

 of 16 days are again subjected to a density of 200, have a significant- 



