Diversity in insect responses to landscape composition drives flower visitation across semi-natural grassland plants

Pollinators have been negatively impacted by agricultural intensification, loss of natural habitats and habitat fragmentation. This has raised concern about the persistence of plant species dependent on insect pollination in semi-natural grasslands where these are remnants of larger grazed areas, now surrounded by intensive agriculture and forests. To better understand landscape composition effects on flower visitation in grassland plant communities visited by a wide range of pollinator groups, we surveyed flowering plants and their flower visitors in 18 semi-natural grasslands in Sweden, along a gradient of proportion of arable crops in the landscape, with systematically varying proportion of permanent semi-natural grassland, forest and ley. Flower visitation was dominated by bumble bees, syrphid flies and non-syrphid flies and depended on the landscape composition. Plant species for which pollinator visits were dominated by bumble bees or flies, but not solitary bees, showed more landscape-dependent flower visitation than plant species with a wider range of visitors. Higher proportion of leys was associated with lower visitation in plants visited by bumble bees and hover flies and higher proportion of permanent grassland with lower visitation in fly-visited plants. In general, a combination of visits from pollinators with contrasting responses to land-use, either at the plant species level (generalist species) or at the plant community level, reduced the sensitivity of flower visitation to the surrounding landscape. We conclude that both diversity and identity of a plant's pollinators will drive strength and direction of pollinator-mediated landscape effects on flower visitation, and likely plant reproduction.