Generalised bumblebee–flower interactions demonstrate weak floral niche partitioning despite a high bee diversity

Niche partitioning is one of the key mechanisms allowing species coexistence and is especially relevant in species‐rich communities. For pollinators, morphology is a major axis in which species differentiate their foraging niche, as it influences the match with flower morphology. Bumblebees Bombus spp. are important pollinators globally, showing their highest diversity of co‐occurring species in the Hengduan Mountains region of southwestern China. This community context makes this region an ideal model system to test the importance of niche partitioning for plant–pollinator interactions. In high‐elevation, flower‐rich meadows, we sampled over four years pollinator–plant interaction networks containing 12 sympatric bumblebee species, varying more than fourfold in tongue length from 4.7 to 21.7 mm. We then assessed the degree of niche partitioning occurring between these bumblebees. We analysed bumblebees' foraging niche widths and overlap, and found that species with longer tongues foraged from a narrower range of flowers. Accordingly, bumblebee species with shorter tongues, who visited a higher diversity of flowering species also showed consistently higher floral overlap with other bumblebee species across years. Despite this morphology‐driven niche pattern for species, the interaction network was consistently characterised by a high degree of generalisation across the years. Our results indicate that the co‐occurrence of a large number of potentially competing pollinators with high generalisation and niche overlap is possible in flower‐rich habitats. We suggest that, in regions of extraordinarily high plant and pollinator diversity and abundance, diverse pollinator communities may also be maintained without strong foraging niche partitioning.