Group Selection, Population Growth Rate, and Competitive Ability in the Flour Beetles, Tribolium Spp.

This is a report of an empirical study of competition between a laboratory strain of Tribolium confusum and populations of T. castaneum selected for increased and decreased productivity by group and individual selection. A pronounced inverse relationship between productivity and competitive ability was observed: fast growing T. castaneum populations had the smallest effect on the ability of T. confusum to recruit adults and slow—growing populations had the largest effect. The average duration of fast—growing T. castaneum populations was prolonged by competition but slow—growing populations were not affected in this regard. Approximately half of the slow—growing populations were facilitated in the production of adults by the presence of a competitor. The data suggest that individual fitness, measured as relative reproductive rate, and population fitness, measured as persistence, may be in conflict. The relevance of these findings to group and individual selection in natural populations is discussed.