bioRxiv preprint doi: https://doi.org/10.1101/2020.03.02.974022; this version posted March 4, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. 1 1 Pollinator niche partitioning and asymmetric facilitation contribute to the 2 maintenance of diversity 3 Na Wei,1,2* Rainee L. Kaczorowski,1 Gerardo Arceo-Gómez,1,3 Elizabeth M. O'Neill,1 Rebecca 4 A. Hayes,1 Tia-Lynn Ashman1* 5 Affiliations: 6 1Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA, USA. 7 2The Holden Arboretum, Kirtland, OH, USA. 8 3Department of Biological Sciences, East Tennessee State University, Johnson City, TN, USA. 9 *Corresponding authors. Email:
[email protected] and
[email protected]. 10 Abstract: 11 Mechanisms that favor rare species are key to the maintenance of diversity. One of the most 12 critical tasks for biodiversity conservation is understanding how plant–pollinator mutualisms 13 contribute to the persistence of rare species, yet this remains poorly understood. Using a process- 14 based model that integrates plant–pollinator and interspecific pollen transfer networks with floral 15 functional traits, we show that niche partitioning in pollinator use and asymmetric facilitation 16 confer fitness advantage of rare species in a biodiversity hotspot. While co-flowering species 17 filtered pollinators via floral traits, rare species showed greater pollinator specialization leading 18 to higher pollination-mediated male and female fitness than abundant species. When plants 19 shared pollinator resources, asymmetric facilitation via pollen transport dynamics benefited the 20 rare species at the cost of the abundant ones, serving as an alternative diversity-promoting 21 mechanism.