Effects of agricultural land use on plant-pollinator interactions in peri- urban grasslands over 3 years

Land use is a major driver for plant-pollinator interactions in grasslands. This study examined abundance and taxa richness of flowering herbs and interacting insects in semi-natural (SN) and successional (SS) grasslands in a peri-urban landscape over 3 years. All insects found on flowers were recorded. Strict pollinating insects included bumblebees (Bombus), hoverflies (Syrphidae), wild bees and honeybees ( Apis mellifera ). We found higher abundances and richness of flowering herbs in SN vs SS grasslands all years. Pollinators had higher abundances at SN sites in 2 out of 3 years, mainly driven by hoverflies. In contrast to our expectations, we found no land use effect on bumblebees. However, bumblebee and strict pollinator abundance correlated with flower abundance, and a linear relationship between bumblebee and herb species diversity suggests that flower resources and diversity are good predictors of pollinator abundance and diversity. Analyses of plant-bumblebee network structure showed higher asymmetry in SS grasslands. SN grasslands scored higher on Shannon diversity and linkage density, which suggests that SS networks are more vulnerable to both plant and bumblebee species loss. Overall, the highest abundance and diversity of flowers and strict pollinating insects were found in SN grasslands, but many plant-pollinator parameters varied more within than among grassland type. Our study identified herb species favored by pollinators, which should be facilitated to increase SN grasslands with high quality flower resources to prevent pollinator declines.