Abstract
Flowering plants require conspecific pollen to reproduce but they often also receive heterospecific pollen, suggesting that pollinators carry mixed pollen loads. However, little is known about drivers of abundance, diversity or composition of pollen carried by pollinators. Are insect-carried pollen loads shaped by pollinator traits, or do they reflect available floral resources? We quantified pollen on 251 individual bees and 95 flies in a florally diverse community. We scored taxonomic order, sex, body size, hairiness and ecological specialization of pollinators, and recorded composition of available flowers. We used phylogenetically controlled model selection to compare relative influences of pollinator traits and floral resources on abundance, diversity and composition of insect-carried pollen. We tested congruence between composition of pollen loads and available flowers. Pollinator size, specialization and type (female bee, male bee, or fly) described pollen abundance, diversity and composition better than floral diversity. Pollen loads varied widely among insects (10–80,000,000 grains, 1–16 species). Pollen loads of male bees were smaller, but vastly more diverse than those of female bees, and equivalent in size but modestly more diverse than those of flies. Pollen load size and diversity were positively correlated with body size but negatively correlated with insect ecological specialization. These traits also drove variation in taxonomic and phylogenetic composition of insect-carried pollen loads, but composition was only weakly congruent with available floral resources. Qualities of pollinators best predict abundance and diversity of carried pollen indicating that functional composition of pollinator communities may be important to structuring heterospecific pollen transfer among plants.
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Data availability
The data was deposited in Dryad Digital Repository https://doi.org/10.5061/dryad.69p8cz90x.
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Acknowledgements
We thank J Rawlins, J Pawelek, R Androw and B Coulter for insect identification, J Hyland and V Verdecia for logistic support at Carnegie Museum of Natural History, and McLaughlin field station staff for logistic support of field work. S O’Neil for insect measurements. We also thank the members of the Ashman lab for discussion, two anonymous reviewers and Jessica Forrest for comments that improved the manuscript.
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This work was supported by the National Science Foundation (DEB 1452386) to T-LA, a DSAS fellowship to N Cullen, and China Scholarship Council funding to J Xia.
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T-LA, RK and GA-G designed field data collection. RK, GA-G, RH, EO and T-LA collected materials from the field. NC and XJ processed data in the laboratory. NW generated the plant phylogeny. NW and XJ contributed guidance to ideas and analysis. NC and T-LA wrote the manuscript.
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Communicated by Jessica Forrest.
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Cullen, N., Xia, J., Wei, N. et al. Diversity and composition of pollen loads carried by pollinators are primarily driven by insect traits, not floral community characteristics. Oecologia 196, 131–143 (2021). https://doi.org/10.1007/s00442-021-04911-0
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DOI: https://doi.org/10.1007/s00442-021-04911-0