Spatial and Temporal Variation in Wild Pollination Service in the Mongolian Steppe

Despite the importance of wild pollination as an ecosystem service, little is known about the spatial and temporal variation of pollination services. Variation in insect pollinator emergence or forb flowers can lead to inconsistent delivery of pollination service to the forb community. A variety of factors, such as air temperature, flower abundance, pollinator abundance, and forb species richness influence the stability of pollination service. All of these factors exhibit spatial and temporal variability. Furthermore, anthropogenic disturbances endanger the persistence of pollination service. To assess the variability of pollination we compared the number of insect flower visits at different locations throughout the summer for two consecutive years in Dalbay Valley, Mongolia. Within this spatio-temporal framework, we investigated the stability of plant-pollinator networks and the effect of ungulate grazing cessation on pollinator visits. Flower visits, forb flower abundance, and measures of plant-pollinator network stability varied greatly over space and time. Hymenoptera visits were positively correlated with only network specialization and Diptera visits were positively correlated with only network nestedness. The exclusion of ungulate grazing altered the composition and abundance of both the forb species and flower visitor communities, but there was no difference in total flower visits between grazed and ungrazed plots. Our results suggest the forb and pollinator community may persist despite the removal of the consistent ungulate grazing pressure. Furthermore, the contribution towards network stability may not be synergistic. Hymenoptera visits were associated with increased network specialization, which tends to lower plant-pollinator network resilience against perturbations, while Diptera visits were associated with increased nestedness, which tends to increase network resilience.