ANIMAL AGGREGATIONS 



405 



ing of the sexes in their random movement 

 (p. 364) through the floury medium. Un- 

 der such conditions the rate of copulation 

 and recopulation is below that at which 

 maximum fecundity occurs. Crombie 

 (1943) gives supporting evidence on this 



bolitim eggs by the older larval and im- 

 aginal members of the population (see p. 

 370; also Chapman and Baird, 1934;. 

 This removal of potential beetles increases 

 in direct proportion to population density 

 (Park, 1933). Also, in overcrowded popu- 



90 iOO HO 



120 130 



20 30 40 50 60 70 80 



GRAMS OF FLOUR 

 F'ig. 142. Optimal initial populations of Tribolium with volume of medium varied. Assays were 

 made after 11 days. (Data from Thomas Park.) 



4 8 16 32 



DENSITY OF POPULATION (Beetles per qm.) 

 Fig. 143. Another test of optimal initial population density in Tribolium. ( Data by MacLagen. ) 



point. Crombie seeded his cultures with 

 well-copulated females specifically selected 

 for high fecundity and, under these condi- 

 tions, found no evidence of undercrowding. 

 The decUne in rate of increase in over- 

 crowding is a result of the eating of Tri- 



lations the females actually produce fewer 

 eggs. Apparently the ovipositing females 

 in crowded cultures have a reduced fecun- 

 dity as a result of "josthng" or other inter- 

 ference by their associates (MacLagan and 

 Dunn, 1936). Crombie (1943, p. 83) sum- 



