Anderson, B.; McCarren, S.; Sabino-Oliveira, A. C.; Lourenco Garcia de Brito, V. G.

Background Pollen production is a costly investment in angiosperm reproduction, yet only a small fraction of grains reach conspecific stigmas. While pollen loss to floral visitors is well studied, the role of abiotic factors in shaping pollen fate has been largely overlooked. Understanding the relative contributions of biotic and abiotic pollen loss pathways is essential for interpreting floral trait evolution and pollination efficiency. Results We quantified abiotic pollen loss in four animal-pollinated species with contrasting floral longevities and reproductive phase dynamics. Flowers were monitored for five hours after anthesis, with pollen loss compared between unvisited flowers and those receiving single pollinator visits. Across all species, substantial pollen loss occurred in the absence of visitation, ranging from 37 - 57% of grains. In several cases, losses to legitimate pollinators were indistinguishable from abiotic loss alone, whereas pollen-foraging honeybees removed significantly greater fractions. Conclusion Abiotic factors can account for a large proportion of total pollen loss, sometimes equalling or exceeding pollinator-mediated removal. These findings challenge the assumption that pollen loss is primarily driven by pollinator activity and suggest that floral traits such as closure, gradual pollen release, and pollen packaging may function as adaptations to minimize environmental loss. Incorporating abiotic pollen loss into studies of pollen presentation and pollinator effectiveness provides a more complete understanding of selective pressures shaping floral evolution.