Dynamic pollinator networks maintain pollination efficiency during mast flowering in an insect-pollinated tree

Jakub Szymkowiak, Michał Bogdziewicz, Waldemar Celary, Łukasz Piechnik, Mateusz Ledwoń, Grażyna Szarek-Łukaszewska, Barbara Seget, Katarzyna Kondrat, Karol Zubek, Magdalena Żywiec

Mast seeding, the synchronous and highly variable reproduction across years, is common among perennial plants, enhancing reproductive success through predator satiation and improved pollination. Animal-pollinated species generally show lower interannual variability in seed production then wind-pollinated plants, often explained by pollinator satiation reducing selection for masting. However, numerous animal-pollinated species mast strongly, challenging this view. We examined pollination dynamics in insect-pollinated Sorbus aucuparia over four years of varying flowering intensity. Pollination efficiency was generally high (mean 68%) across years and increased from ~20% to ~80% with increasing tree-level flower abundance, showing no decline in high-flowering periods. Instead, pollinator visitation networks shifted significantly: Bombus species, capable of quick numerical and functional responses, dominated visits during abundant flowering years. In contrast, bees such as Andrena and Lasioglossum subg.Evylaeus, limited by univoltine life cycles, were proportionally more important during low-flowering years. Our findings highlight that pollinator life histories shape visitation networks and stabilize pollination across mast cycles. More generally, our results suggest that animal pollination does not prevent the evolution of masting but rather reduces its selective pressure, emphasizing wind pollination as the primary driver behind the evolution of strong masting due to its high pollen transfer requirements.