Diversity and habitat use by stingless bees (Apidae) in the Brazilian Atlantic Forest

The present study discusses spatial variations in the community structure of stingless bees as well as associated ecological factors by comparing the nest densities in two stages of forest regeneration in a Brazilian Tropical Atlantic rainforest. The stingless bee nests were sampled in sixty-four 25 x 25 m plots (4 ha) in four replicates of two forest categories: (a) mature, or old growth, stage of forest regeneration and (b) early-stage forest regeneration. Tree cavities were the major nesting substrate, and 91 nests were found within the total sampling area of 32 ha (2.8 nests/ha), constructed by 12 stingless bee species. The four most abundant species showed no significant differences in terms their use of tree circumference at breast height (CBH) categories between 60 and 150 cm. The spatial distributions of the CBH categories were mainly random or uniform, and the principal difference between the forest stages was the density of their largest trees (CBH > 110 cm). This structural difference in the vegetation contrasted with the small spatial variation (p > 0.05) of the stingless bee community structure (species composition, richness, and nest abundance). This unexpected spatial homogeneity could be related to similar and abundant availabilities of the largest nesting sites and to the existence of similar mechanisms controlling cavity use in both forest categories. The low nest-per-tree frequency (1 nest per 100 trees with CBH > 60 cm), for instance, suggests that the availability of tree nesting sites is not limiting stingless bees. Alternatively, the stochasticity that permeates the temporal dynamics of highly diverse tree communities may also neutralize any latent competition between stingless bees.