How do different bumblebees choose flowers in a biodiversity hotspot, the Himalaya-Hengduan Mountains?

Huan Liang, Yan-Hui Zhao, Nicole E. Rafferty, Zong-Xin Ren, Li Zhong, Hai-Dong Li, De-Zhu Li, Hong Wang

Different bumblebee species visiting different wildflowers in the study sites.
Different bumblebee species visiting different wildflowers in the study sites.

Bumblebees are ecologically and economically important due to their general foraging patterns and adaptation to cold environments. Wild bumblebee populations are experiencing declines due to multiple interacting factors, such as habitat loss and climate change. However, plant-bumblebee interaction networks have seldom been studied in the mountains around the Qinghai-Tibetan plateau, the principal hotspot for bumblebee species diversity worldwide. As species interactions are known to be shaped by both evolutionary history and ecological factors, we used an approach that incorporates the evolutionary histories of both plants and bumblebees, along with abundance, phenology (seasonal timing), and 13 floral and bumblebee functional traits. We also tested whether trait matching in two pairs of plant-bumblebee traits explained interaction frequencies at both species- and individual-levels.

  We found that evolution plays a role in shaping bumblebee flower choices. Closely related bumblebees tended to visit similar sets of plants, but not vice versa, i.e. closely related plant species did not tend to attract the same bumblebee species. Among all the measured factors, nectar volume and sugar concentration were the most important for explaining such interaction patterns. Although long-tongued bumblebee species tended to visit long-tubed flowers, trait matching did not predict short-tongued bee interaction frequencies. Despite this, trait matching was apparent at the level of individual bees, reflecting intraspecific variation in tongue length and body size. Together, these findings provide new evidence for the importance of nectar rewards in structuring interaction patterns in pollination mutualisms. The results also demonstrate that trait matching may occur at the individual level, despite not being detectable at the species level, and underline the necessity of taking intraspecific trait variation into account in studies of community structure.

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