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A systems approach reveals urban pollinator hotspots and conservation opportunities

Abstract

Urban areas are often perceived to have lower biodiversity than the wider countryside, but a few small-scale studies suggest that some urban land uses can support substantial pollinator populations. We present a large-scale, well-replicated study of floral resources and pollinators in 360 sites incorporating all major land uses in four British cities. Using a systems approach, we developed Bayesian network models integrating pollinator dispersal and resource switching to estimate city-scale effects of management interventions on plant–pollinator community robustness to species loss. We show that residential gardens and allotments (community gardens) are pollinator ‘hotspots’: gardens due to their extensive area, and allotments due to their high pollinator diversity and leverage on city-scale plant–pollinator community robustness. Household income was positively associated with pollinator abundance in gardens, highlighting the influence of socioeconomic factors. Our results underpin urban planning recommendations to enhance pollinator conservation, using increasing city-scale community robustness as our measure of success.

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Code availability

The modelling code used in the robustness models is available upon request from the corresponding author.

Data availability

The data that support the findings of this study are available within the article and Supplementary Information (see Supplementary Tables 19 and Supplementary Data 15). Supplementary Data 1 contains pollinator and floral abundance and richness data that support Figs. 1 and 2. Supplementary Data 2 contains data used in the socioeconomic analyses. The data used in the floral null model analyses are presented in Supplementary Data 3, and the model outputs are summarized in Supplementary Tables 7 and 8. Supplementary Data 4 contains data used in Figs. 3 and 4 as well as Supplementary Figs. 35. Supplementary Data 5 contains data used in the robustness models.

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Acknowledgements

This research was supported by the UK Insect Pollinators Initiative, funded by the BBSRC, Defra, the NERC, the Scottish Government and the Wellcome Trust under the auspices of the Living with Environmental Change partnership: grant BB/I00047X/1 (www.urbanpollinators.org). We thank M. Pavett, J. Deeming, B. Levey, M. Wilson, R. Morris and R. Barnett for taxonomic expertise, and land owners and managers for access to sites. We thank S. Bettoni, P. Cannard, S. Cartwright, R. Comont, E. Elliot, C. Grey, P. Harris, R. Harris, B. Jarrett, K. Mikolajczak, V. Miravent, H. Morse, E. Moss, P. Ouvrard, L. Riggi, V. Radhakrishnan, D. Roumpeka, F. Sinclair, M. Stone and V. Williams for assistance with field data collection. This work is based on data provided through Ordnance Survey, the Office for National Statistics, the UK Data Service (EDINA UKBORDERS and Casweb MIMAS), Natural England, the Countryside Council for Wales and Scottish Natural Heritage, and uses boundary material which is copyright of the Crown. Census output is Crown copyright and is reproduced with the permission of the Controller of HMSO and Queen’s Printer for Scotland.

Author information

The study was conceived by J.M. and designed with input from all authors. Fieldwork was carried out by K.C.R.B., M.A.G., D.M.H., N.M., H.M., L.M.O. and K.M.R., with local teams supervised by J.M., G.N.S., S.G.P. and W.E.K. K.C.R.B., I.P.V. and P.P.A.S. carried out the analyses. K.C.R.B. and J.M. led the writing of the manuscript. All authors contributed to drafts of the manuscript and gave final approval for publication.

Correspondence to Katherine C. R. Baldock.

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Supplementary information

Supplementary Information

Supplementary Methods, Supplementary Figures 1, 2 and 5, Supplementary Tables 1–6, 9 and 10, and Supplementary References

Reporting Summary

Supplementary Figure 3

Heat maps of estimated city-scale floral abundances. High-resolution file of Fig. 4a–d. Crown copyright and database rights 2018 Ordnance Survey (100025252)

Supplementary Figure 4

Heat maps of estimated city-scale pollinator abundances. High resolution file of Fig. 4e–h. Crown copyright and database rights 2018 Ordnance Survey (100025252)

Supplementary Table 7

Null model results for all plant taxa in all four cities

Supplementary Table 8

Null model standardised effect sizes (SES) for all plant taxa by city

Supplementary Data 1

Data set on pollinator and floral abundance and richness that supports analyses in Results section ‘Abundance, occurrence and richness of pollinating insects and plants’ and used to create Figs. 1 and 2 and Supplementary Fig. 5

Supplementary Data 2

Data set on pollinator and floral abundance and richness in gardens that supports analyses in Results section ‘Household income level’

Supplementary Data 3

Data sets used for null model analyses in Results section ‘Plant selection by pollinating insects’

Supplementary Data 4

Data set used to calculate values used in Results section ‘Scaling to the city level’ and for Figs. 3 and 4, and Supplementary Figs. 3–5

Supplementary Data 5

Data sets used in robustness models in Results section ‘Network models and management strategies’

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Further reading

Fig. 1: Pollinator abundance and richness for the nine urban land uses in four cities.
Fig. 2: Floral abundance and richness for the nine urban land uses in four cities.
Fig. 3: Land use proportions and estimated numbers of pollinators per land use at a city scale for four cities.
Fig. 4: Heat maps of estimated city-scale floral and pollinator abundances.
Fig. 5: Predicted increase in city-scale plant–pollinator network robustness for two management strategies.