Pollinator community composition and pollen resource use in calcareous grasslands under different landscape contexts across Europe

Plants and pollinators interact in complex ways to facilitate plant reproduction and increase insect fitness. While some plant and insect species show high levels of specialization, others engage in more generalized interaction patterns. However, interactions between plants and pollinators are dynamic and can change in response to altered environmental conditions. Land-use change is one of the main factors that may affect the interactions between plants and insects, as the associated shifts in land cover, habitat availability, and habitat connectivity are expected not only to directly impact pollinator and plant diversity, but also to influence the foraging behaviour and resource use of pollinators. In this study, we compared pollinator community composition, pollinator resource use and the structure of the network of plant-pollinator interactions among calcareous grasslands embedded in agricultural landscapes differing in grassland amount, connectivity and surrounding land use across five European countries. Pollinator surveys were conducted to assess variation in their communities, while pollen metabarcoding was conducted to assess the interactions between plants and pollinators. Network analyses were used to investigate whether the overall structure of the network of interactions differed between landscapes. Our results show substantial differences in pollinator communities and pollen composition between grasslands, leading to strong interaction turnover. However, despite strong species turnover, dominant families such as Asteraceae (plants) and Syrphidae (insects) remained consistently common across sites, suggesting considerable functional redundancy. In addition, pollinators consistently foraged on plant species in the wider landscape, regardless of variations in landscape composition and habitat connectivity. This likely contributed to the limited differences in overall network structure, with similar levels of connectance, nestedness, and modularity across landscapes. Synthesis. Overall, these findings indicate that pronounced differences in pollinator communities and opportunistic foraging strategies resulted in large interaction turnover, but these shifts did not translate into major changes in overall network structure, likely due to functional redundancy. Future long-term monitoring studies are needed to assess whether these network properties remain stable through time under continued landscape change.