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.