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

Pollinator sharing among plants within a community can have a variety of consequences, including the transfer of heterospecific pollen (HP) to stigmas, a process hypothesized to be phenotype (at the species and community levels) and flower density-mediated. In a tropical highland community, we investigated whether species’ HP receipt depends on species trait means and/or their trait similarity to other species in the community. We also tested whether HP received by individuals is affected by floral density and if so, at what scale. Density responses in HP receipt were then integrated into species trait analysis to determine whether trait patterns persisted across scales after accounting for density. We found that 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 primarily by flower density, which is scale-dependent, while species traits and their similarity to the community play a secondary role.