Pollination across the diel cycle: a global meta-analysis

The daily transition between day and night, known as the diel cycle, is characterised by significant shifts in environmental conditions and biological activity, both of which can affect crucial ecosystem functions like pollination. Yet, despite over six decades of research into whether plant reproductive success varies between day and night, consensus remains elusive. We compiled and analysed the evidence of diel pollination differences from 135 studies with pollinator exclusion experiments across 139 angiosperms using phylogenetically controlled multilevel meta-analytic models and tested the influence of environmental conditions and plant functional traits. Our synthesis revealed an overall lack of difference in pollination success between day and night, suggesting generalization across the diel cycle. However, diel variation was partially explained by elevation, such that nocturnal pollination success was greater at low elevations, whereas diurnal pollination was more beneficial at higher elevations. Furthermore, plant traits related to pollinator attraction (odour, colour), and anthesis time influenced diel variation in pollination success. In the light of increasing anthropogenic pressures on biodiversity, as well as unique challenges for nocturnal biota, this synthesis underscores the complementarity of pollinators for flowering plants across the diel cycle, and the importance of considering both nocturnal and diurnal pollinators in conservation efforts.