Pollen presentation mitigates competition for pollinators due to diurnal stratification of pollen transfer

Abstract

Pollen presentation and release strategies are believed to affect the timing of plant-pollinator interactions and therefore play a crucial role in pollen transfer. However, only limited evidence links pollen release and temporal changes in the pollen load carried by pollinators. In the present study, we aim to investigate how different pollen presentation strategies affect both the quantity and quality of pollen transferred by plant pollinators and discuss the potential for structuring plant-pollinator networks. We investigated pollen load on pollinators collected from three co-flowering species during the daytime with a known pollen presentation strategy: Succisa pratensis releasing pollen early in the morning, Centaurea jacea employs a gradual pollen presentation and Trifolium hybridum with explosive pollen release during pollinator visits. We compared the temporal patterns in the number of conspecific pollen grains (pollen of visited plant species) on the bodies of pollinators(pollen quantity) and in the proportions of the total pollen load (pollen quality) for different pollinators of the studied plant species. Then we linked pollen transfer to the pollinator visitation pattern during the day.The three plant species differed in the pattern of pollen transfer by their pollinators. Pollinators of Succisa pratensis carried the majority of the pollen in the morning after the pollen was released followed by a drop in both pollen quantity and quality. Pollinators of C. jacea and T. hybridum carried less variable pollen loads over time, which we explain by plant spatial density (C. jacea) and flower morphology combined with a pollen release strategy (T. hybridum). By linking the diurnal pattern of pollen transfer with the pollinator visitation pattern, our results demonstrate the diurnal structuring of pollen transfer and the plant’s ability to mitigate the negative effect of pollinator sharing.