Growth, distribution, and competition of Tribolium castaneum and Tribolium brevicornis in fine-grained habitats

The growth and distribution of single- and mixed-species cultures of Tribolium castaneum and T. brevicornis maintained in fine-grained habitats defined by the proportion of standard and corn oil media were examined. The growth patterns of the single species cultures were qualitatively different. For the corn oil-sensitive strain of T. castaneum, the initial adult-pupa coordinates were drastically modified by corn oil medium, which appeared to stabilize the approach to demographic equilibrium. For T. brevicornis, the presence of corn oil patches extended the duration of the oscillations in these coordinates. Although niche breadth and overlap measures revealed different species utilization of the media types, T. castaneum excluded T. brevicornis in all test habitats. These single and mixed species observations were interpreted in the context of the usual cannibalism model for the regulation of population numbers with the addition of a newly identified adult-larval interaction in T. brevicornis. The primary intraspecific effect of this interaction is the elimination of oscillations in larval numbers. The interspecific effect is that T. castaneum adults mimic this adult-larval interaction of T. brevicornis and thereby prevent larval metamorphosis. Diversity of the culture medium is not enough for these species to coexist. The large larvae of T. brevicornis apparently need a refugium from the adults of T. castaneum.