Using a Centrality Index to Determine the Contribution of Restored and Volunteer Plants in the Restoration of Plant-Pollinator Mutualisms on a Reclaimed Strip Mine

The restoration of ecosystem function relies, at least partly, on restoring services provided by mutualists. If the goal of restoration is to assemble functional and stable communities, particular care should be taken to identify and attract those species that contribute most to long-term community stability. Land managers and ecologists can use centrality indices, a group of network statistics that measure the relative importance of individuals within a community, to objectively determine the contribution of particular plant species to overall restoration efforts. Our objective was to compare the role of flowers planted as part of the restoration effort to those plants volunteering at the restoration site, either native adventives or non-native invaders, in support of the pollinator community. Further, we sought to determine how this relationship varied with changes in relative floral abundance. We found that plants cultivated as part of the restoration effort were preferred by pollinators, attracted the greatest abundance and richness of pollinators, and were the most central in our plant-pollinator networks compared to volunteers, despite the greater abundance of volunteer plants across the site. We also found that the role of all plants was density dependent; plants of every group attracted more pollinators in plots where they had greater relative abundance. We conclude that centrality indices provide a tool for planning and monitoring the restoration of important functional relationships and allow land managers and ecologists to objectively determine the contribution of particular plants to overall community structure and function.