Effect of Flower Clumping on Defense of Artificial Flowers by Aggressive Stingless Bees

Abstract

Certain species of stingless bees are highly aggressive and defend floral food sources, especially when the flowers occur in locally dense patches. An experiment with two bee species, Trigona silverstriana and Trigoona corvina, exploiting a large number of artificial baits, tested the effect of grouping the baits on the success of aggressive defense. Spacing or clumping the baits made no difference in the numbers of the dominant bee species (T. silvestriana) visting the experimental site. However, the numbers of the rival bee species (T. corr'ina) were reduced dramatically when the baits were clumped, because of more effective distribution of defending T. silv estriana bees. STINGLESS BEES, common in the tropics, are social insects which exhibit broad overlap in the floral resources they exploit (Johnson 1974; see Leppik 1955, Wille 1963, Bawa 1975 for examples). There is evidence that many of these bee species are food limited (Hubbell and Johnson 1977) and that intraspecific and interspecific competition for food routinely occurs (Johnson 1974, 1980; Johnson and Hubbell 1974). The variety in foraging behavior and worker communication in these bee species (Hubbell and Johnson 1978, Lindauer and Kerr 1960, Kerr and Esch 1965) suggests that coexistence may depend on partitioning according to differences in timing, persistence, renewal rate, and spatial dispersion of their food resources. Such partitioning can even be accomplished on the variability that occurs among individual plants of the same species. In spite of general synchrony of flowering in populations of tropical trees (Janzen 1967; Daubenmire 1972; Frankie, Baker, and Opler 1974), trees exhibit considerable intraspecific variation in number of flowers offered on a given day, timing of flower opening, nectar or pollen reward, and spatial dispersion (Bawa 1975, Carpenter 1976, Eldridge 1976, Hedgegart 1976, Hubbell 1979). Johnson and Hubbell (1975) hypothesized that permits coexistence between the stingless bee species Trigona fuscipennis and T. fulviveintris. They found T. fuscipennis to be a highdensity specialist that forages in groups and visits only the densest clumps of flowers. Trigona fulviventris, on the other hand, is a low-density specialist that frequently forages alone on more-dispersed flowers. Density specialization with group foraging by the high-density specialist has subsequently been found in desert ants (Davidson 1977), a circumstance which suggests that it may be a common feature of foraging in eusocial insects that communicate the location of food sources. An assumption of the model for density specialization is that species adapted for exploiting the high-density resources control access to these resources. In stingless bees such control is exerted by groups of bees aggressively sequestering high-density resources. Johnson and Hubbell (1975) argued that the suitability of aggressive group foraging for highdensity spatially aggregated food sources was not only that such food sources provided sufficient food returns for all defending bees, but also that such food sources could be effectively guarded against rival