To test several hypotheses concerning the optimal life-history characteristics expected to be associated with individuals encountering primarily high or low population density, we scored flying behavior, development time, fecundity, and competitive ability in two populations of flour beetles (Tribolium castaneum) differentiated with respect to emigration behavior as a result of artificial selection. We observed a significant difference between the selection lines in flying ability which was in the same direction as the difference in emigration rate. No difference between the selection lines was detected for fecundity, but significant differences were observed for development time and competitive ability. These differences were in the directions predicted by theoretical work. That is, individuals more likely to encounter low density situations through increased dispersal tendencies develop faster and are poorer competitors than individuals likely to remain in areas maintaining large populations. The correlations among development time, competitive ability, and dispersal ability appear to be the result of genetic correlations among these characteristics, and suggest that fitness values associated with combinations of these lifehistory traits are a function of population density.