Effects of different types of low-intensity management on plant-pollinator interactions in Estonian grasslands

In the face of global pollinator decline, extensively-managed grasslands play an important role in supporting stable pollinator communities. However, different types of extensive management may promote particular plant species and thus particular functional traits. As the functional traits of flowering plant species (e.g. flower size and shape) in a habitat determine the identity and frequency of pollinator visitors, they can also influence the structures of plant-pollinator interaction networks. The aim of this study was to examine how the type of low-intensity traditional management influences plant and pollinator composition, the structure of plant-pollinator interactions, and their mediation by floral and insect functional traits. Specifically, we compared mown wooded meadows to grazed alvar pastures in western Estonia. We found that both management types fostered equal diversity of plants and pollinators, and overlapping, though still distinct, plant and pollinator compositions. Wooded meadows had significantly higher connectance and specialisation, while alvar pastures achieved higher Shannon diversity at a standardised sampling of interactions. Pollinators with small body sizes and short proboscis lengths were more specialised in their preference for particular plant species and the specialisation of individual pollinators was higher in alvar pastures than in wooded meadows. All in all, the two management types promoted diverse plant and pollinator communities, which enabled the development of equally even and nested pollination networks. The same generalist plants and pollinators were important for the pollination networks of both wooded meadows and alvar pastures; however, they were complemented by management-specific species, which accounted for differences in network structure. Therefore, the implementation of both management types in the same landscape helps to maintain high species and interaction diversity.