The role of functional diversity and facilitation in small-scale pollinator habitat

People in urban and rural areas are planting habitat patches for pollinators in response to growing public awareness of the risks of pollinator declines; yet research rarely has been undertaken to inform the composition of such patches. Determining which key functional plant traits to prioritize and how plant-pollinator interaction dynamics operate in these small-scale, fragmented patches is critical to ensuring the efficacy of pollinator restoration efforts across landscapes. We established small-scale (2.5 m diameter) experimental patches and manipulated plant diversity and resource level (nectar) to determine the effects on pollinator abundance, pollinator diversity, and plant-pollinator facilitation-competition dynamics. Our results showed that in small-scale habitat, plant diversity and resource availability significantly affected the abundance and diversity of pollinating insects. Specifically, the treatments that contained high-resource plant species increased pollinator abundance and diversity the most. Plant diversity increased pollinator diversity and abundance only in the absence of high-resource plants. Pollination facilitation was observed in high-resource treatments, but varied among plant species. Competition for pollinators was observed in high-diversity treatments but did not affect seed set for high-resource plants in any of the treatments. Our results suggest that managers or landowners planting small-scale pollinator habitat should prioritize including species with high nectar production, and secondarily, a diverse mix of species if space and resources allow. The protocols we used to monitor pollinators can be used by community science observers with limited training, expanding the potential for assessment of future pollinator habitat restoration projects. Shared research identifying features critical to effective restoration will help conserve plant-pollinator mutualisms across landscapes.