Pollination Under Pressure: Grazing and Nutrient Enrichment Reshape Arctic Pollinator Communities and Interaction...

Pollinators are declining globally due to anthropogenic pressures, such as intensive grazing and nutrient enrichment. Yet, their combined effects on pollinators and plant-pollinator interactions remain poorly understood, particularly in the Arctic. Here, we experimentally tested how grazing exclusion and nutrient addition shape flower-visiting insect communities and interaction networks in a high-productivity montane and a low-productivity tundra grassland, in northern Fennoscandia. Grazing exclusion emerged as the primary driver across both grasslands, increasing flower-visitor family richness, diversity, and the number of plant-pollinator interactions. These effects were especially strong in the tundra grassland, where resource limitation is more pronounced. In contrast, nutrient addition had weaker and more context-dependent effects, enhancing flower-visitor richness and the number of interactions mainly in the tundra grassland and particularly when combined with grazing exclusion. At both sites, grazing exclusion and nutrient addition altered community composition, with the strongest shifts occurring under their combined effects. Despite large effects on interaction numbers, network structure responded more subtly. Weighted connectance declined with grazing exclusion, especially in the tundra, indicating that interactions became more concentrated on a subset of plant species where floral resources were abundant. In contrast, network specialization (H₂') and nestedness showed limited responses to experimental treatments, suggesting relatively stable interaction organization. Overall, our results demonstrate that grazing strongly regulates pollinator communities and interaction networks in Arctic grasslands, while nutrient enrichment plays a secondary, context-dependent role. The pronounced sensitivity of tundra grasslands highlights their vulnerability to environmental change and underscores the importance of managing grazing pressure to sustain pollination processes in Arctic ecosystems.