Floral trait dissimilarity indirectly decreases heterospecific pollen transfer through pollinator sharing in a subalpine meadow.

Abstract

Co-flowering species are suggested to exhibit divergent floral traits to minimize interspecific competition. However, few studies have evaluated whether and by which pathways floral trait dissimilarity affects interspecific pollen transfer among co-flowering species, which limits our understanding of the interplay between mutualistic and competitive interactions within plant-pollinator networks. We conducted a three-year field investigation from 2021 to 2023 in a sub-alpine meadow in southwest China. We observed plant-pollinator interactions and identified pollen grains on the stigmas of co-flowering species to construct plant-pollinator visitation networks and heterospecific pollen transfer (HPT) networks. We also measured 18 floral traits across 44 co-flowering species, categorizing these traits into attractant traits (flower color spectra, corolla morphology) and reproductive traits (male and female organs). By calculating the dissimilarities in each floral trait category between species pairs, we conducted structural equation modeling to link the dissimilarities in floral traits between species pairs with pollinator sharing and HPT. Our results demonstrated that dissimilarities in flower color and corolla morphology significantly reduced pollinator sharing, and indirectly decreased HPT. Conversely, the dissimilarities in male and female-organ traits did not have a significant impact on HPT or pollinator sharing. Our findings support the theory that divergent floral traits help reduce interspecific competition, highlighting the adaptive significance of floral trait divergence in plant-pollinator interactions.