104 THE SOCIAL LIFE OF ANIMALS 



duction per female when more than the minimal 

 pair is present. I have a strong suspicion, however, 

 that one would get a more rapid rate of increase per 

 number of animals involved if, instead of keeping 

 the sexes equal in numbers, there were a ratio, let 

 us say, of two females to one male. 



We do know that with Drosophila the greatest 

 numbers are produced when the feeding surface is 

 relatively great but not too great; (60) this result may 

 be explained by the assumption that with too great 

 space, or in other words, with too few flies present, 

 wild yeasts or molds grow more rapidly than the 

 Drosophila can keep under control. 



Another well-studied laboratory animal, the flour 

 beetle, Triholium, under certain experimental con- 

 ditions gives most rapid population growth at an 

 intermediate population size rather than with too 

 few or too many present. A study of data collected 

 by Chapman showed that in a flour beetle's little 

 world, a microcosm of thirty-two grams of flour, these 

 beetles, during the early stages of population growth, 

 reproduce most rapidly per female with two pairs 

 present (Figure 17). Reproduction is more rapid 

 when four pairs or even sixteen pairs are present, 

 than if there is only one pair. (3) 



This work of Dr. Chapman's was done for another 

 purpose. We took it for an indication of possibilities. 



