i8o 



ANIMAL AGGREGATIONS 



ment of the population the greatest increase comes with an initial 

 population of 4, while the least rapid rate of reproduction comes with 

 the smallest number of individuals present. 



This indicates, as did the data of Petersen, that there is an opti- 

 mum initial population-medium relationship, which, for certain 



8- 



1^ 



1 - 



Z 4 8 16 32 64 



Initial population per 52 g/ns. of f/our 



Fig. 13. — Showing the relation of initial density of Tribolium population in 32 gm. 

 of flour to rate of reproduction. Recalculated from data reported by Chapman. 



volumes of medium, is different from that given by the smallest 

 population present. The fact here seems as clear as could be expect- 

 ed from an experiment not designed to test this particular point. 

 More recently T. Park, working in this laboratory, has confirmed 

 Chapman's results (unpublished data). The explanation is even less 

 apparent than in the case of Robertson's phenomenon in the Pro- 

 tozoa. 



