An experimental analysis of competitive indeterminacy in Tribolium

This report reexamines experimentally the problem of competitive indeterminacy in mixed-species populations of the flour beetles, Tribolium confusum and T. castaneum. Indeterminacy takes the form of alternative competitive outcomes: in some replicate cultures one species exterminates the other with a probability, say p, whereas in others, the opposing species wins with a complementary probability, 1-p. The conventional explanation for this is the genetic founder effect hypothesis--an explanation based on genetic stochasticity. The experiment reported here partitioned indeterminacy into founder effect and nonfounder effect components. The results implicate demographic stochasticity, not classical genetic founder effect, as a factor influencing the identity of the winning species.