Distribution and pollination services of wild bees and hoverflies along an altitudinal gradient in mountain hay meadows

Extensively managed and flower‐rich mountain hay meadows, hotspots of Europe's biodiversity, are subject to environmental and climatic gradients linked to altitude. While the shift of pollinators from bee‐ to fly‐dominated communities with increasing elevation across vegetation zones is well established, the effect of highland altitudinal gradients on the community structure of pollinators within a specific habitat is poorly understood. We assessed wild bee and hoverfly communities, and their pollination service to three plant species common in mountain hay meadows, in eighteen extensively managed yellow oat grasslands (Trisetum flavescens) with an altitudinal gradient spanning approx. 300 m. Species richness and abundance of pollinators increased with elevation, but no shift between hoverflies and wild bees (mainly bumblebees) occurred. Seedset of the woodland cranesbill (Geranium sylvaticum) increased with hoverfly abundance, and seedset of the marsh thistle (Cirsium palustre) increased with wild bee abundance. Black rampion (Phyteuma nigrum) showed no significant response. The assignment of specific pollinator communities, and their response to altitude in highlands, to different plant species underlines the importance of wild bees and hoverflies as pollinators in extensive grassland systems. To date, the effects of highland altitudinal gradients, within a specific habitat type, on pollinator community structures are poorly understood. We thus evaluate community structures of wild bees and hoverflies and their consequences for pollination services throughout a highland altitude gradient in mountain hay meadows. Our results clearly support a similar response to altitude for both pollinator taxa when sampled in the same grassland habitat type.