Floral traits and density are drivers of heterospecific pollen deposition in a biodiverse tropical highland community

Pollinator sharing among plants within a community can have a variety of consequences. Pollinator movement among different plant species, in particular, can result in heterospecific pollen (HP) transfer to stigmas, a process that is hypothesized to be phenotype (at the species and community levels) and flower density mediated. In a tropical highland community, we investigated which species-specific (floral tube length, flower size, stigma height, stigma exposure, pollination system, floral abundance) and community-related reproductive traits (distinctiveness of stigma to anther height, of floral color, and flowering synchrony) mediate species HP receipt (mean intensity and proportion). We also tested whether HP received by individuals is affected by floral density and if so, at what scale. Species with stigmas more exposed and with functionally specialized pollination received more HP, and species flowering more synchronously to the community received greater proportions of HP. At the individual level, HP proportion depended on the interaction between conspecific and heterospecific flower densities, with outcomes varying by scale. At the local scale (within 2m²), low to medium conspecific flower abundance increased the proportion of HP receipt with the increase of heterospecific floral density, while high conspecific and heterospecific floral densities reduced HP. Conversely, at the landscape scale (across 202m²), high conspecific and heterospecific floral densities enhanced the proportion of HP, while low to medium densities had no effect. Our results demonstrate that HP is widespread in the community, driven by species-specific and community-related traits, as well as by flower density, which is scale-dependent.