Impacts of local and landscape grassland management on the structure of plant-pollinator networks

Abstract

Grassland management under local-scale results-based agri-environmental payment schemes (RBAPSs) are designed to benefit some biodiversity groups like plants. However, it is unknown if RBAPSs affect plant-pollinator interaction networks, and whether local or landscape management is more influential. Most studies focus on traditional community structure measures like richness, neglecting the impacts management may have on network structure and stability, and thereby ecosystem function. Plant species that benefit from RBAPSs could also act as key forage plants for pollinators, but this has not been investigated.We sampled networks across 23 grasslands in the West of Ireland to investigate if grassland management at local (RBAPS) and/or landscape scale (proportion of semi-natural grassland) influence network size, connectance, nestedness, linkage density and specialization of networks. Species strength analysis was used to identify key plant species for bumblebees, solitary bees, hoverflies, and butterflies.Results indicate RBAPSs benefit network size and linkage density, where species-rich grasslands supported larger networks and higher linkage densities. Networks surrounded by higher proportions of semi-natural grassland also had larger network sizes and higher linkage densities. Nestedness was greater in landscapes with high proportions of improved grassland. Key plant species differed between pollinator groups.Our results highlight that managing grasslands to promote greater plant diversity through a local scale RBAPS positively influences the structure and stability of networks, with possible implications for pollination service delivery. However, networks are also influenced by landscape management suggesting that local-scale management by itself may not be sufficient to conserve networks. We conclude that measures aimed at pollinators should include grassland management at both spatial scales where possible and to promote the establishment of key plant species to help sustain a wider range of pollinator taxa.