Pollen metabarcoding reveals broad and species-specific resource use by urban bees.

Caitlin Potter,Col R Ford,Matthew J Hegarty,Laura E Jones,Natasha De Vere,Anita Diaz,Elizabeth L Franklin,Kathy H Hodder

doi:10.7717/peerj.5999

Abstract

Bee populations are currently undergoing severe global declines driven by the interactive effects of a number of factors. Ongoing urbanisation has the potential to exacerbate bee declines, unless steps are taken to ensure appropriate floral resources are available. Sown wildflower strips are one way in which floral resources can be provided to urban bees. However, the use of these strips by pollinators in urban environments remains little studied. Here, we employ pollen metabarcoding of the rbcL gene to compare the foraging patterns of different bee species observed using urban sown wildflower strips in July 2016, with a goal of identifying which plant species are most important for bees. We also demonstrate the use of a non-destructive method of pollen collection. Bees were found to forage on a wide variety of plant genera and families, including a diverse range of plants from outside the wildflower plots, suggesting that foragers visiting sown wildflower strips also utilize other urban habitats. Particular plants within the wildflower strips dominated metabarcoding data, particularly Papaver rhoeas and Phacelia tanacetifolia. Overall, we demonstrate that pollinators observed in sown wildflower strips use certain sown foodplants as part of a larger urban matrix.

Highlights

IntroductionWild bee populations have suffered widespread declines in the form of substantial range contractions (Kerr et al, 2015) alongside local decreases in the abundance and species richness of hoverfly and bee communities (Biesmeijer et al, 2006; Potts et al, 2010; Bommarco et al, 2011; Cameron et al, 2011; Dupont, Damgaard & Simonsen, 2011; Bartomeus et al, 2013)
We used high-throughput sequencing of the rbcL gene to characterise pollen collected from wild bees which were captured while foraging in sown wildflower strips within urban areas during July 2016, demonstrating the applicability of recently developed ‘metabarcoding’ techniques to assessing the effectiveness of conservation methods
Despite the fact that all bees sampled were collected in wildflower strips, a number of them were found to utilise species not present in wildflower strips, highlighting the role that gardens play in providing adequate floral resources for urban bees

Summary

Introduction

Wild bee populations have suffered widespread declines in the form of substantial range contractions (Kerr et al, 2015) alongside local decreases in the abundance and species richness of hoverfly and bee communities (Biesmeijer et al, 2006; Potts et al, 2010; Bommarco et al, 2011; Cameron et al, 2011; Dupont, Damgaard & Simonsen, 2011; Bartomeus et al, 2013). Wild bee declines likely result from the interactive effects of multiple factors (Goulson et al, 2015), including habitat loss and fragmentation (e.g. due to urbanisation; Garibaldi et al, 2011; Gerard et al, 2010; Hendrickx et al, 2007; NEA, 2011), climate change (Kerr et al, 2015) and parasite and pathogen spread (Otterstatter & Thomson, 2008). While the global number of managed honeybee colonies has increased (Aizen & Harder, 2009), this is unlikely to be sufficient to compensate for wild pollinator losses: the rate of increase currently does not match the rate of increase in the need for pollinator services (Aizen & Harder, 2009) and certain regions are experiencing a reduction in numbers of beekeepers and managed honeybee colonies (National Research Council, 2007; Potts et al, 2010)

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