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D1c. Status of pollinating insects

Type: State / Benefit indicator

Introduction

This indicator indicates changes in pollinator distribution (bees and hoverflies) in the UK. The indicator is based on 389 species (154 species of bee and 235 species of hoverfly), and measures change in the number of 1 km grid squares across the UK in which they were recorded in any given year: this is referred to as the ‘occupancy index’. Many insect species are involved in pollination but bees and hoverflies are known to be important and are presented here as an indicator of overall pollinator trend.

Key results

The headline indicator for all pollinators, the index for hoverflies and the index for wild bees have all been updated since the 2021 publication with the time series extending to 2019 (two additional years for the headline and hoverflies indices, and one additional year for the wild bees index).  Since the previous publication all indicators have been produced with a new methodology. New methods were used to select species based on the suitability of the underlying data for producing occupancy trends with acceptable precision, and a novel statistical approach for combining species trends into an indicator was applied (Freeman et al. 2020). These changes have caused the uncertainty estimation around the index to be smaller, and for the historic decline to be less severe. See the background section and the technical background document for further detail on the production of this indicator.

There was an overall decrease in the pollinator indicator from 1987 onwards. In 2019, the indicator had declined by 21% compared to its value in 1980. The long-term trend was assessed as declining (Figure D1ci).

Between 2014 and 2019, the indicator showed a decrease of 6%; as a result, the short-term trend was assessed as declining.

Over the long term, 16% of pollinator species became more widespread (8% showed a strong increase), and 42% became less widespread (20% showed a strong decline). Over the short term, a greater proportion of species were declining (48%; with 33% exhibiting a strong decline) than increasing (27%; with 17% exhibiting a strong increase).

Figure D1cia. Trend in the distribution of UK pollinators, 1980 to 2019.

A line chart showing an overall decrease in the pollinator indicator from 1987 onwards. In 2019, the indicator had declined by 21% compared to its value in 1980.

A bar chart showing over the long term, 16% of pollinator species became more widespread (8% showed a strong increase), and 42% became less widespread (20% showed a strong decline). Over the short term, a greater proportion of species were declining (48%; with 33% exhibiting a strong decline) than increasing (27%; with 17% exhibiting a strong increase).

Notes:

  1. The index used in the indicator update in 2022 includes 389 species (154 wild bee and 235 hoverfly species); the number of species can vary between years.
  2. Figure D1cia (the line graph) shows the unsmoothed composite indicator trend with variation around the line (shaded) within which users can be 90% confident that the true value lies (credible interval).
  3. Figure D1cib (the bar chart) shows the percentage of species within the indicator that have increased, decreased or shown little change in occupancy, based on set thresholds of change (see supporting technical document).
  4. This indicator was not updated in the 2021 publication. For this publication (2022) the time series has been extended by two additional years (to 2019) and a new methodology has been applied to the whole time series.

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

Assessment of change in the distribution of pollinators in the UK

  Long term Short term Latest year
Distribution of UK pollinators

Deteriorating
1980–2019


2014–2019

Decreased (2019)

Note: Analysis of the underlying trends is carried out by the data providers. See Assessing Indicators.

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Indicator description

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 wider range of crops and wild flowers. Despite the inter-annual variation, the overall trend for pollinators remains downward.

The indicator occupancy index was also produced for the bee (Figure D1cii) and hoverfly (Figure D1ciii) species separately. The wild bee index fluctuates around its initial value over much of the time series, and in 2019 it was estimated to be 2% higher than in 1980. A larger proportion of bee species have decreased than increased over the long term (33% decreased and 22% increased), as well as over the short term (37% decreased and 28% increased).

Figure D1ciia. Trend in the distribution of wild bee species in the UK, 1980 to 2019.

A line chart showing the wild bee index fluctuating around its initial value over much of the time series. In 2019 it was estimated to be 2% higher than in 1980.

A bar chart showing that a larger proportion of bee species have declined than increased over the long term (33% declined and 22% increased), as well as over the short term, (37% declined and 28% increased).

Notes:

  1. The index used in the indicator update in 2022 includes 154 wild bee species; the number of species can vary between years.
  2. Figure D1ciia (the line graph) shows the unsmoothed composite indicator trend with variation around the line (shaded) within which we can be 90% confident that the true value lies (credible interval).
  3. The figure in brackets shows the number of species included in the index.
  4. Figure D1ciib (the bar chart) shows the percentage of species within the indicator that have increased, decreased or shown little change in occupancy, based on set thresholds of change.
  5. Since the 2021 publication, there was no update to the length of the time series, however this indicator has been updated to take account of a new methodology.

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

There was a decline in the bee index from 2007 to 2014. Loss of foraging habitat is understood to be a major driver of change in bee distribution (Vanbergen et al., 2014) and pesticide use has been shown to have an effect on bee behaviour and survival (Stanley et al., 2015). Weather effects, particularly wet periods in the spring and summer, are also likely to have had an impact. Further research would help to better understand the relative importance of these potential drivers of change.

With regard to hoverflies, the index was at a peak in 1987 (108% compared to its 1980 value), and then (apart from some minor increases), underwent a progressive decline and is 33% lower in 2019 than in 1980.

A greater proportion of hoverflies have declined than increased in occupancy over both the long and short term (1980 to 2019: 47% decreased and 13% increased; 2014 to 2019: 54% decreased and 28% increased). It is not clear why hoverflies show a different trend to bees, although differences in the life cycle will mean they respond differently to weather events and habitat change.

Figure D1ciiia. Trend in the distribution of hoverfly species in the UK, 1980 to 2019.

A line chart showing the hoverflies index peaked in 1987 (108% compared to its 1980 value), and then (apart from some minor fluctuations), underwent a progressive decline and is 33% lower in 2019 than in 1980.

A bar chart showing a greater proportion of hoverflies have declined than increased in occupancy over both the long and short term (1980 to 2019: 47% decreased and 13% increased; 2014 to 2019: 54% decreased and 28% increased).

Notes:

  1. The index used in the indicator update in 2022 includes 235 hoverfly species; the number of species can vary between years.
  2.  Figure D1ciiia (the line graph) shows the unsmoothed composite indicator trend with variation around the line (shaded) within which we can be 90% confident that the true value lies (credible interval).
  3. Figure D1ciiib (the bar chart) shows the percentage of species within the indicator that have increased, decreased or shown little change in occupancy, based on set thresholds of change.
  4. This indicator was not updated in the 2021 publication. For the 2022 publication the time series has been extended by two additional years (to 2019) and a new methodology has been applied to the whole time series.

Source: Biological Records Centre (supported by UK Centre for Ecology & Hydrology and Joint Nature Conservation Committee); Hoverfly Recording Scheme.

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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 flowers. Bees and hoverflies are also popular insects and people enjoy seeing them in towns, cities and the wider countryside. Insect pollination depends on the abundance, distribution and diversity of pollinators. Knowledge of the population dynamics and distribution of those species that provide the service, the pollinators, helps us assess the risk to these values. Many wild bees and other insect pollinators have become less widespread, particularly those species associated with semi-natural habitats. At the same time, a smaller number of pollinating insects have become more widespread. This may have implications for the pollination service they provide to crops and wild flowers, and is an area of active research (Potts et al., 2010; Garratt et al., 2014).

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Background

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.

The indicator is the average trend across all 389 species included in the analysis. Individual species within the indicator will have different time-series trends (that is, some may be increasing while others may show strong declines). The shaded region on Figures D1ci, D1cii and D1ciii is the 90% credible interval of the annual occupancy estimates and represents the statistical uncertainty surrounding the annual occupancy estimates. Credible intervals are similar to the confidence intervals used in parametric statistics, but are the appropriate metric to use with Bayesian statistics. Estimates will be revised as new data become available.

The Bayesian occupancy approach is an established analytical method that enables an estimation of species occurrence even though the data utilised in this indicator were collected without a standardised survey design (van Strien et al., 2013; Isaac et al., 2014). For each species, records were extracted at the 1 km grid cell scale with day precision, 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. Uncertainty in the species-specific annual occupancy estimates is represented by the 90% credible intervals. See the technical background document for further detail on the production of this indicator.

The composite indicator was produced using a novel hierarchical modelling method for calculating multi-species indicators developed by UKCEH (Freeman et al. 2020). The new method offers several advantages over the simple geometric mean used previously (see the technical background document for more details). Crucially, this method uses a smoothing process to reduce the impact of between-year fluctuations – such as those caused by variation in weather – making underlying trends easier to detect. This has resulted in a much smoother trend and smaller magnitude of decline since 1980 when compared to the indicator published in 2021. In addition, the index values produced by the new method are more precise (narrower ribbon of uncertainty): this is one reason why the short-term assessment (last five years) has switched from “Little or no change” in 2021 to “Deteriorating” in 2022).

As species become more or less widespread, individual grid squares will have richer (more species) or poorer (fewer species) pollinator communities; pollination services are generally likely to 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. National level data on changes in abundance of pollinators is not currently available.

The short-term trends tend to have fewer species falling into the ‘stable’ category than the long-term trends. This is likely to be a result of the high level of short-term variation in invertebrate populations. The species-specific trends were calculated as the mean percentage change in occupancy per year. Therefore, across a 39-year period, the influence of short-term variation on the trend is reduced compared to its influence on a shorter five-year period.

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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 Target 14 icon

Target 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 Target 7 icon

Target 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 Target 15 icon

Target 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.

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Reference Title
Bees, Wasps & Ants Recording Society BWARS homepage
Centre for Ecology and Hydrology

Biological Records Centre homepage

Defra The National Pollinator Strategy: for bees and other pollinators in England (PDF, 3.37MB)
Hoverfly Recording Scheme HRS homepage

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References

Garratt, M. P. D., Truslove, C. L., Coston, D. J., Evans, R. L., Moss, E. D., Dodson, C., Jenner, N., Biesmeijer, J. C. and 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. and 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. and 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. and 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. and 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. and Hanley, N. (2013). Status and Value of Pollinators and Pollination Services. Report to DEFRA.

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Downloads

Download the Datasheet and Technical background document from JNCC's Resource Hub.

An Evidence Statement (2016) is available on Defra's website.

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Last updated: December 2022

Latest data: 2019

 

This content is available on request as a pdf in non-accessible format. If you wish for a copy please go to the enquiries page.

Categories:

UK Biodiversity Indicators 2022

Published: .

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