Phenotypic, Floristic, and Anthropogenic Drivers of the Pollen Niche of Amazonian Stingless Bees

Stingless bees (Apidae: Meliponini) are major pollinators in the tropics, supporting key ecosystem services. Yet, stingless bee impact on pollination depends on how many and which pollen types they use, and the relative importance of different factors affecting bee choice for pollen is uncertain. Further, empirical syntheses on bee–plant interactions have largely neglected the Amazon, where stingless bees are major pollinators. Here, we tested phenotypic, environmental, and anthropogenic effects on stingless bee pollen niche across the Brazilian Amazon. We assembled literature data on 242 pollen types collected by 36 species of stingless bees, which were sampled across 1450 km during 1975 to 2012. In this study, the pollen niche is defined by two dimensions: the number and set of pollen taxa collected by stingless bees, representing diversity and composition of the gathered pollen. We modeled the response of the pollen diversity and composition to (1) bee species body mass, (2) tree diversity, (3) tree composition, (4) rainfall, (5) urbanization, and (6) sampling year while accounting for the pollen sampling method, pollen taxonomic uncertainty, and bee phylogenetic relatedness. Pollen diversity decreased with body mass and over time but was higher in urban compared to wild colonies. Pollen composition changed with body mass, tree composition, and year. These relationships were independent of colony sampling method and bee phylogeny and were robust even under uncertainty in pollen taxonomic identification. We show that larger stingless bees are more selective foragers, but much of the variation in their pollen niche across the Brazilian Amazon reflects urbanization, plant resources, and geographical patterns in climate. The long-term change of stingless bee pollen niche can have serious consequences for pollination in the region.