Natural Selection in Experimental Populations of Tribolium. III. Characteristics of Tribolium confusum Populations in Equilibrium

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Abstract
Two groups of the flour beetle, Tribolium confusum, derived from two different strains, were maintained for 80 weeks in population cages from which weekly census samples were removed and analyzed. After about 40 weeks the populations reached an equilibrium and during the following weeks the numbers of adults were found to be about 20% greater in populations of one group than in the other, and the number of pupae about twice as great. In the larger populations, natalities were estimated to be higher and adult life spans shorter, and the two population groups were also found to differ in the interactions between fecundity and adult density. The analyses revealed the presence of characteristics leading to density dependent control of population size and preventing rapid and complete exploitation of the environment. This was construed as an adaptation of a granary insect to a uniform unreplenished environment. Variations in the characteristics, generated initially by genetic differences and amplified by population interactions, evinced retention by the species of the adaptive variability necessary for the maintenance of population fitness.