Pollen foraging and resource partitioning of stingless bees in relation to flowering dynamics in a Southeast Asian tropical rainforest

We used microscopic pollen analysis to investigate the diversity and similarity of pollen diets of six colonies of stingless bees (Apidae; Meliponini) located within one monospecific (three colonies of Trigona collina) and one mixed nesting aggregation (one colony of T. collina, and one colony of each of the close relatives T. melina and T. melanocephala) in lowland tropical rain forest in Sabah, Malaysia. Samples of 20 corbicular loads, collected six times over a period of three months from each colony, contained a total of 74 different morphotypes of pollen grains with an average between 4.7 to 8.5 per sample for the different colonies. In an analysis on total diet composition intraspecific similarity was much greater than interspecific similarity. The focal colony of Trigona collina from the mixed aggregation distinctly clustered according to species rather than nest location, suggesting that some interspecific resource partitioning occurs. The sampling period was accompanied by a drastic increase in flowering activity as evidenced by data from a flower phenology transect. At times of limited flowering similarity of pollen diets was generally low, both within and between species. It is hypothesized that this is so because bees are forced to forage from scattered subsets of flower patches spread out over a large foraging range. In times of increased flowering pollen diet similarity significantly increased between colonies of the monospecific aggregation, presumably because colonies concentrated on more profitable sources in closer proximity. In contrast, similarity remained low within the mixed aggregation, suggesting that innate differences in foraging preferences precluded any effect of diet convergence.