D1. Biodiversity and ecosystem services

D1c. Status of pollinating insects

 

Type: State / Benefit indicator

 

Summary

Figure D1ci.  Change in the distribution of UK pollinators, 1980 to 2010.

Figure D1ci. Change in the distribution of UK pollinators, 1980 to 2010.

Notes:

  1. Based on a total of 213 pollinators, comprising 105 wild bee species and 108 hoverfly species.
  2. The line graph shows the unsmoothed trend (dashed line) and smoothed trend (solid line), with variation around the line (shaded) within which it is 90 per cent likely that the true value exists (credible interval).
  3. The bar chart shows the percentage of species within the indicator that have increased, decreased, or shown no change in occupancy, based on set thresholds of change.

Source: Bees, Wasps & Ants Recording Society; Hoverfly Recording Scheme; Biological Records Centre (supported by Centre for Ecology & Hydrology and Joint Nature Conservation Committee).

 

Assessment of change in the distribution of pollinators in the UK

 

Long term

Short term

Latest year

Distribution of UK pollinators

indicator declining
1980–2010

indicator declining
2005–2010

Decreased (2010)

 

  • The indicator shows the average relative change in distribution of 213 species of pollinator, as measured by the number of 1km grid squares across the UK in which they were recorded – this is referred to as the ‘occupancy index’.
  • Based on the unsmoothed data, there was an overall decrease in the indicator from 1987 onwards.  The occupancy index fell by 32 per cent between 1980 and 2010.
  • Between 1980 and 2010, 27 per cent of pollinator species become more widespread (14 per cent showed a strong increase), and 51 per cent became less widespread (36 per cent showed a strong decrease).  Similar patterns occurred between 2005 and 2010, but with a greater proportion increasing and decreasing strongly.
  • As individual pollinator species become more or less widespread, the communities in any given area become more or less diverse, and this may have implications for pollination as more diverse communities are, in broad terms, more effective in pollinating a wide range of crops and wild flowers.

 

Indicator description

The indicator illustrates changes in pollinator distribution (bees and hoverflies) in the UK between 1980 and 2010.  The indicator is based on 213 species of pollinator (105 species of bee and 108 species of hoverfly), and measures change in the number of 1km grid squares across the UK in which they were recorded – this is referred to as the ‘occupancy index’.  Bees and hoverflies are key pollinators and are presented here as an indicator of overall pollinator trend.  Other taxonomic groups (e.g. some butterflies and moths) can provide pollination services but are not yet included in the indicator.

The pollinator indicator fell by 32 per cent between 1980 and 2010.  More specifically, there has been a steady decrease in pollinator occupancy from 1987 onwards.  A greater proportion of species were showing negative trends in occupancy over both the long- and short-term than were increasing (Figure D1ci).

As species become more or less widespread, individual grid squares will have richer (more species) or poorer (fewer species) pollinator communities; pollination services will generally be higher where the pollinator community is richer (Vanbergen et al. 2013).  The area occupied does not necessarily relate to pollinator abundance, as a species with one individual in each of 10 grid squares would receive the same occupancy score as a species with 100 individuals in each of the same grid squares, although generally, species with greater occupancy are likely to be more abundant.

The short-term trends tend to have a far greater number of species falling into the “stronger” categories than the long-term trends.  This is likely to be a result of the high level of short-term variation in invertebrate populations, however, the significance of this phenomenon is unclear.  The species-specific trends were calculated as the mean percentage change in occupancy per year, therefore across a 30 year period, the influence of short-term variation on the trend is reduced compared to its influence on a five year trend.

The shaded region on Figure D1ci is the 90 per cent credible interval of the annual occupancy estimates and represents the uncertainty surrounding the annual estimates.  Credible intervals are similar to the confidence intervals used in parametric statistics, but are the appropriate metric to use with Bayesian statistics.  The solid line illustrates a smoothed trend.

 

 

Relevance

Nature is essential for human health and well-being.  Pollination is an important ecosystem service that benefits agricultural and horticultural production, and is essential for sustaining wild flower biodiversity; bees and hoverflies are popular insects.  Pollination depends on the abundance, distribution and diversity of pollinators.  It is therefore important to assess the population dynamics and distribution of those species that provide the service: the pollinators.  Wild bees and other insect pollinators are probably less abundant in total than they were in the 1950s, and many species have become less widespread, particularly those species associated with semi-natural habitats.  At the same time, a smaller number have become more widespread.  This may have implications for the pollination service they provide to crops and wild flowers (Potts et al. 2010; Garratt et al. 2014).

Occupancy of pollinators refers to the overall area where each species is found and does not refer directly to their abundance.  The reduction in the index shows that overall pollinators are becoming more restricted in their distributions so that on average in any one place the diversity of pollinator species found is reduced.  This does not necessarily mean that the abundance of pollinators has declined, as some species may have become more abundant.  National level data on changes in abundance of pollinators is not currently available.

 

Background

The indicator is the average trend across all 213 species included in the analysis.  Individual species within the indicator will have different time-series trends (i.e. some may be increasing while others may show stronger declines).  The credible intervals reflect the uncertainty of the annual occupancy estimates.  Estimates will be revised when new data become available.

The Bayesian occupancy approach enables an estimation of species occurrence even though the data utilized in this indicator were collected without a standardized survey design (van Strien et al. 2013; Isaac et al. 2014).  For each species, records were extracted at the 1km grid square scale with records on different days being treated separately, and an annual time-series of the proportion of sites occupied was calculated.  Each species-specific time-series was scaled so the first value in 1980 was set to 100.  The annual index (the pollinator occupancy indicator) was estimated as the arithmetic mean of the scaled species-specific occupancy estimates.  Each species was given equal weighting within the indicator, but because of data gaps not all species contribute to every year of the data.  Uncertainty in the species-specific annual occupancy estimates is represented by the 90 per cent credible intervals.  See the technical background document for further detail on production of the indicator.

The occupancy index was also produced for the bee (Figure D1cii) and hoverfly (Figure D1ciii) species separately.  The wild bee index was relatively stable up to 2005, it then increased before a sharp decline.  The wild bee index fell by 38 per cent between 1980 and 2010.  The occupancy index was declining for a greater number of wild bee species than were increasing over both the long- and short-term.  The sharp decline in the occupancy index in the three years up to 2010 of the indicator plot is reflected in the large (70 per cent) proportion of wild bee species showing strong declines in occupancy over the short-term.

 

Figure D1cii.  Change in the distribution of wild bee species in the UK, 1980 to 2010.

Figure D1cii. Change in the distribution of wild bee species in the UK, 1980 to 2010

Notes:

  1. Based on 105 wild bee species.
  2. The line graph shows the unsmoothed trend (dashed line) and smoothed trend (solid line), with variation around the line (shaded) within which it is 90 per cent likely that the true value exists (credible interval).
  3. The bar chart shows the percentage of species within the indicator that have increased, decreased, or shown no change, based on set thresholds of change.

Source: Bees, Wasps & Ants Recording Society; Hoverfly Recording Scheme; Biological Records Centre (supported by Centre for Ecology & Hydrology and Joint Nature Conservation Committee).

 

In contrast to the bees, the hoverfly index (Figure D1ciii) shows a gradual decline from 1987 to 2007 onwards, it fell by 41 per cent between 1980 and 2007.  This trend was reversed in the last three years; overall between 1980 and 2010 the indicator fell by 24 per cent.  A greater proportion of hoverflies have declined in occupancy over the long-term than have increased, but in the short-term 59 per cent of hoverflies show strong increases in occupancy between 2005 and 2010.

 

Figure D1ciii.  Change in the distribution of hoverfly species in the UK, 1980 to 2010.

Figure D1ciii. Change in the distribution of hoverfly species in the UK, 1980 to 2010.

Notes:

  1. Based on 108 hoverfly species.
  2. The line graph shows the unsmoothed trend (dashed line) and smoothed trend (solid line), with variation around the line (shaded) within which it is 90 per cent likely that the true value exists (credible interval).
  3. The bar chart shows the percentage of species within the indicator that have increased, decreased, or shown no change, based on set thresholds of change.

Source: Bees, Wasps & Ants Recording Society; Hoverfly Recording Scheme; Biological Records Centre (supported by Centre for Ecology & Hydrology and Joint Nature Conservation Committee).

 

The annual variability in the data is likely to be partly explained by annual variation in weather conditions.  Pollinators tend to respond positively to increased temperature but negatively to rainfall.  Hot dry periods are likely to have a greater negative impact on hoverflies than bees, as the exposed larvae of hoverflies are more vulnerable to desiccation compared to the larvae of bees that tend to be protected within an enclosed nest.  The recent decline in bees from 2007–2010 is striking.  A number of pressures are known to impact on local pollinator behaviour, distribution and abundance: weather, climate, land use change and pesticide use, for example (Vanbergen et al. 2014; Stanley et al. 2015).  There was a decline in the indicator between 2007 and 2010.  It is not known whether this change in distribution is the start of a longer-term trend or short-term fluctuation, and if the former, whether it is linked to one particular pressure or to a combination of pressures.  Despite the inter-annual variation, the overall trend for pollinators remains downward.

In 2015-16, Defra commissioned a project (reference BE0112), to provide evidence statements to accompany a number of species trend indicators and an overview of the causes of biodiversity change. The output from this project is contained in a methods report, drivers of change report, and summary of evidence.  These are summarised indicator by indicator in a set of Evidence Statements, which aim to ensure that interpretation of trends, casual factors and relationship to policy interventions is rigorous, objective and reflects scientific consensus.

In parallel with the Evidence Statements, Defra also commissioned a Quality Assurance Panel to provide advice on improvements that could be considered to the species based indicators in the UK and England biodiversity indicator sets. The report of the review has led to an action plan of changes to be made as resources allow.

 

Further development

Bees and hoverflies are key pollinators in the UK and are presented here as an indicator of the overall trend in pollinators.  Other taxonomic groups (e.g. some butterflies and moths) can provide pollination services but are not yet included in the indicator.  Future updates of the pollinator indicator could include trends from other taxonomic groups known to provide pollination services.

All species are given equal weight in the pollinator indicator; effectively the indicator assumes all species are equally valuable in terms of their contribution to pollination services.  However, contribution to pollination is known to vary between species and is dependent on inherent characteristics of the species, but also on total population abundance (Breeze et al. 2011; Woodcock et al. 2013).  Future work could examine the feasibility of weighting the indicator to take account of this variation in species importance as pollinators.

 

Goals and targets

Aichi Targets for which this is a primary indicator

Strategic Goal D. Enhance the benefits to all from biodiversity and ecosystems.

Aichi icon 14Target 14: By 2020, ecosystems that provide essential services, including services related to water, and contribute to health, livelihoods and well-being, are restored and safeguarded, taking into account the needs of women, indigenous and local communities, and the poor and vulnerable.

 

Aichi Targets for which this is a relevant indicator

Strategic Goal B. Reduce the direct pressures on biodiversity and promote sustainable use.

Aichi icon 7Target 7: By 2020 areas under agriculture, aquaculture and forestry are managed sustainably, ensuring conservation of biodiversity.

 

Strategic Goal D. Enhance the benefits to all from biodiversity and ecosystems.

Aichi icon 15Target 15: By 2020, ecosystem resilience and the contribution of biodiversity to carbon stocks has been enhanced, through conservation and restoration, including restoration of at least 15 per cent of degraded ecosystems, thereby contributing to climate change mitigation and adaptation and to combating desertification.

 

Web links for further information

Reference

Title

Website

Bees, Wasps & Ants Recording
Society

BWARS homepage

http://www.bwars.com/

Hoverfly Recording Scheme

HRS homepage

http://hoverfly.org.uk/portal.php

Centre for Ecology & Hydrology

Biological Records Centre
homepage

http://www.brc.ac.uk/

Department for Food, Environment & Rural Affairs

The National Pollinator Strategy: for bees and other pollinators in England

https://www.gov.uk/government/uploads/
system/uploads/attachment_data/file/370199/
pb14221-national-pollinator-strategy.pdf

Defra Evidence Statements project: Method report http://sciencesearch.defra.gov.uk/Document.aspx?Document=13933_BE0112FinalReport.pdf
Defra Evidence Statements project: Drivers of Change http://sciencesearch.defra.gov.uk/Document.aspx?Document=13945_Annex2_DriversOfChange.pdf
Defra Evidence Statements project: Summary of Evidence http://sciencesearch.defra.gov.uk/Document.aspx?Document=13947_Annex3_SummaryOfEvidence.pdf
Defra Quality Assurance Science Panel report View QASP report

 

References

Breeze, T.D., Bailey, A.P., Balcombe, K.G. & Potts, S.G. (2011) Pollination services in the UK: How important are honeybees? Agriculture, Ecosystems & Environment, 142, 137–143.

Garratt, M.P.D., Truslove, C.L., Coston, D.J., Evans, R.L., Moss, E.D., Dodson, C., Jenner, N., Biesmeijer, J.C. & Potts, S.G. (2014) Pollination deficits in UK apple orchards. Journal of Pollination Ecology, 12, 9–14.

Isaac, N.J.B., van Strien, A.J., August, T.A., de Zeeuw, M.P. & Roy, D.B. (2014) Statistics for citizen science: extracting signals of change from noisy ecological data. Methods in Ecology and Evolution, 5, 1052–1060.

Potts, S.G., Biesmeijer, J.C., Kremen, C., Neumann, P., Schweiger, O. & Kunin, W.E. (2010) Global pollinator declines: trends, impacts and drivers. Trends in Ecology & Evolution, 25, 345–53.

Stanley, D.A. Garratt, M.P.D., Wickens, J.B., Wickens, V.J., Potts, S.G. & Raine, N.E. (2015) Neonicotinoid pesticide exposure impairs crop pollination services provided by bumblebees. Nature, online.

Van Strien, A.J., van Swaay, C.A.M. & Termaat, T. (2013) Opportunistic citizen science data of animal species produce reliable estimates of distribution trends if analysed with occupancy models. Journal of Applied Ecology, 50, 1450–1458.

Vanbergen, A., Heard, M., Breeze, T., Potts, S. & Hanley, N. (2013) Status and Value of Pollinators and Pollination Services. Report to DEFRA.

Woodcock, B.A., Edwards, M., Redhead, J., Meek, W.R., Nuttall, P., Falk, S., Nowakowski, M. & Pywell, R.F. (2013) Crop flower visitation by honeybees, bumblebees and solitary bees: Behavioural differences and diversity responses to landscape. Agriculture, Ecosystems & Environment, 171, 1–8.

 

 

Download Datasheet

Download Technical background document

Download Technical background document on Bayesian Occupancy Models

Download Evidence statement

 

Last updated: November 2016

Latest data: 2010