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

We used microscopic pollen analysis to investigate the diversity and simila rity of pollen diets of six colonies of stingless bees (Apidae; Meliponini) located within one monospecific (three colonies of Trigona collina) and on e mixed nesting aggregation (one colony of T. collina, and one colony of ea ch of the close relatives T. melina and T. melanocephala) in lowland tropic al rain forest in Sabah, Malaysia. Samples of 20 corbicular loads, collecte d six times over a period of three months from each colony, contained a tot al 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 s imilarity. The focal colony of Trigona collina from the mixed aggregation d istinctly clustered according to species rather than nest location, suggest ing that some interspecific resource partitioning occurs. The sampling peri od was accompanied by a drastic increase in flowering activity as evidenced by data from a flower phenology transect. At times of limited flowering si milarity 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 incr eased between colonies of the monospecific aggregation, presumably because colonies concentrated on more profitable sources in closer proximity. In co ntrast, similarity remained low within the mixed aggregation, suggesting th at innate differences in foraging preferences precluded any effect of diet convergence.