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Author(s): Na Wei [sup.1] [sup.2] , Rainee L. Kaczorowski [sup.1] , Gerardo Arceo-Gómez [sup.1] [sup.3] , Elizabeth M. O'Neill [sup.1] , Rebecca A. Hayes [sup.1] , Tia-Lynn Ashman [sup.1] Author [...], Mechanisms that favour rare species are key to the maintenance of diverse communities.sup.1-3. One of the most critical tasks for conservation of flowering plant biodiversity is to understand how plant-pollinator interactions contribute to the maintenance of rare species.sup.4-7. Here we show that niche partitioning in pollinator use and asymmetric facilitation confer fitness advantage of rarer species in a biodiversity hotspot using phylogenetic structural equation modelling that integrates plant-pollinator and interspecific pollen transfer networks with floral functional traits. Co-flowering species filtered pollinators via floral traits, and rarer species showed greater pollinator specialization leading to higher pollination-mediated male and female fitness than more abundant species. When plants shared pollinator resources, asymmetric facilitation via pollen transport dynamics benefitted the rarer species at the cost of more abundant species, serving as an alternative diversity-promoting mechanism. Our results emphasize the importance of community-wide plant-pollinator interactions that affect reproduction for biodiversity maintenance. The authors show that plant-pollinator interactions confer a fitness advantage to rare plant species in a biodiversity hotspot.

Nicotiana section Alatae exhibits great diversity among species in floral morphology, mating system, and predominant pollinators. As a first step towards estimating nectar's role in floral evolution, we studied nectar traits to determine whether they vary in association with predominant pollinators and mating system. Dally phenology determines when nectar becomes available to pollinators and differed between hummingbird- and moth-pollinated species. Nectar volume and concentration varied significantly among most species and pollinator groups, but were inversely correlated, so that total energy was similar among most species. In general, nectar volume was positively correlated with corolla length. The autogamous species, N. plumbaginifolia, had a nectar volume that matched expectations based on corolla length, but with lower concentration and total energy than predicted by corolla length, while nectar volume was lower than predicted by corolla length in the autogamous population of N. longiflora. Sugar and amino acid components (determined through HPLC) were similar among species, although differences did exist. The nectar of most species was sucrose-dominant, but the autogamous N. plumbaginifolia had nectar that contained similar proportions of sucrose, glucose, and fructose. Many nectar traits varied in association with the predominant pollinators and, in some cases, with the mating system. Key words: amino acids; Argentina; Brazil; hummingbirds; moths; nectar; Nicotiana; Solanaceae.