C4b. Status of UK priority species – Distribution
Type: State Indicator
This indicator was not updated in 2023. It was last updated in 2021.
Introduction
This indicator measures change in the number of one kilometre grid squares across the UK in which priority species were recorded in any given year. This is referred to as the ‘occupancy index’ and is effectively equivalent to changes in the distribution of priority species for which data are available. Priority species are defined as those appearing on one or more of the biodiversity lists of each UK country (Natural Environmental and Rural Communities Act 2006 - Section 41 (England), Environment (Wales) Act 2016 section 7, Northern Ireland Priority Species List, Scottish Biodiversity List). The combined list contains 2,890 species in total. The priority species were highlighted as being of conservation concern for a variety of reasons, including rapid decline in some of their populations. The indicator will increase when priority species become more widespread on average, and decrease when species become less widespread on average.
This indicator should be read in conjunction with C4a which provides data on those species for which abundance data are available.
Key results
Official lists of priority species have been published for each UK country. There are 2,890 species on the combined list; actions to conserve them are included within the respective countries’ biodiversity or environment strategies.
Since the 2020 publication, the Biological Records Centre has received additional data for Aquatic bugs, Empid & Dolichopodid Flies, Ephemeroptera, Plecoptera and Trichoptera. These data are included in this year’s indicator.
Between 1970 and 2018, the index of distribution of priority species in the UK decreased, with a higher proportion of species decreasing in distribution than increasing. The long-term trend is assessed as a decline of 4%.
The index was 2% lower in 2018 than in 2013, with 18% of species showing an increase and 36% showing a decline. However, this short-term decrease was not significant, and therefore the short-term assessment is little or no change.
Figure C4bi. Change in distribution of UK priority species, 1970 to 2018
Notes about Figure C4bi:
- The line graph shows the smoothed trend (solid line) with variation around the line (shaded area) within which users can be 95% confident that the true value lies (credible interval). The width of the credible interval (CI) is in part determined by the proportion of species in the indicator for which data are available.
- The figure in brackets shows the number of species included in the composite index.
- The bar chart shows the percentage of species within the indicator that have increased, decreased or shown little change in distribution (measured as the proportion of occupied sites), based on set thresholds of change.
- All species in the indicator are present on one or more of the country priority species lists (Natural Environmental and Rural Communities Act 2006 – Section 41 (England), Environment (Wales) Act 2016 section 7, Northern Ireland Priority Species list, Scottish Biodiversity List).
- These charts are not directly comparable to previous versions of the indicator. Inclusion of new data has increased the number of species that can be included in the indicator from 422 in 2020, to 476 here. Additionally, novel methods to combine individual species trends into the multi-species indicator have been applied in 2021.
Source: Biological records data collated by a range of national schemes and local data centres.
Assessment of change in distribution of priority species in the UK
| Long term | Short term | Latest year | |
| Priority species – Distribution |
Little or no overall change 1970–2018 |
Little or no overall change 2013–2018 |
No change (2018) |
Notes for Assessment of Change table:
Analysis of the underlying trends is undertaken by the data providers.
Indicator description
Priority species are defined as those appearing on one or more of the biodiversity lists of each UK country (Natural Environmental and Rural Communities Act 2006 - Section 41 (England); Environment (Wales) Act 2016 section 7, Northern Ireland Priority Species List, Scottish Biodiversity List). The combined list contains 2,890 species in total. The priority species were highlighted as being of conservation concern for a variety of reasons, including rapid decline in some of their populations. Actions to conserve these priority species are included within the respective countries’ biodiversity or environment strategies.
Of the 2,890 species on the combined priority species list, the 476 for which robust quantitative time-series of the proportion of occupied sites are available are included in the indicator. These 476 species include bees, wasps and ants (95); bryophytes and lichens (128); moths (122); and other taxa (131). The other taxa include a number of insect groups, non-marine molluscs and spiders. The species have not been selected as a representative sample of priority species and they cover only a limited range of taxonomic groups. The measure is therefore not fully representative of species in the wider countryside. See the technical background document for more detail.
The relative change in distribution of each of these species is measured by the number of 1 kilometre grid squares across the UK in which they were recorded – this is referred to as the ‘occupancy index’. The occupancy index will increase when a species becomes more widespread; it will decrease when a species becomes less widespread.
The index of distribution of priority species in the UK shows a decline of 6% between 1970 and 1986, after which it increases slightly to 103 in 2004, before decreasing again to its current value of 96 relative to its baseline figure in 1970. The occupancy of priority species is assessed as stable between 1970 and 2018. The index is 4% lower in 2018 than in 1970; this is not considered a significant decrease, although the overlap of the 95% credible intervals with the baseline index in 1970 is very marginal. The indicator decreased by 2% between 2013 and 2018, it is assessed as stable when taking into account the 95% credible interval. Uncertainty in the species-specific annual occupancy estimates are incorporated into the overall indicator; details of how this was done are included in the technical background document.
Relevance
Priorities for species and habitat conservation are set at a country level through country biodiversity or environment strategies. Each country has an identified list of priority species, which are of high conservation concern due, for example, to restricted range or population declines. The indicator therefore includes a substantial number of species that, by definition, are becoming less widespread.
Measures of distribution are less sensitive to change than measures of abundance (see indicator C4a). Nonetheless, if a threatened species that has been declining starts to recover, its distribution should stabilise, and may start to increase. If the proportion of species in the indicator that are stable or increasing grows, the indicator will start to decline less steeply. If the proportion declines, it will fall more steeply. Success can therefore be judged by reference to trends in both indicators C4a and C4b, as well as other information on other priority species for which there are insufficient data for inclusion in the indicator.
Background
The measure is a composite indicator of 476 species from 22 taxonomic groups (eight of the 30 groups originally modelled did not contain any species with sufficient data to be included in the final analysis), see the technical background document for further detail on production of the indicator. The priority species identified in each of the four UK countries were highlighted as being of conservation concern for a variety of reasons, including their scarcity, their iconic nature or a rapid decline in their population. They are not representative of wider species in general. They do however include a range of taxonomic groups and will respond to the range of environmental pressures that biodiversity policy aims to address, including land use change, climate change, invasive species and pollution. The short-term assessment of change can be used to assess the impact of recent conservation efforts and policy aimed at halting and reversing species declines. However, natural fluctuations (particularly in invertebrate populations) and short-term response to weather may have a strong influence on the short-term assessment.
Regardless of advances in statistical techniques and the increase in the number of biological records collected, there are likely to be species on the priority lists for which little monitoring or occurrence data is available. Reasons for this include rarity, difficulty of detection, or those for which monitoring methods are unreliable or unavailable. In order for the indicator to be representative of priority species, a method of assessing the changing status of these remaining data-poor species would need to be considered.
The Bayesian occupancy approach enables an estimation of species occurrence even though the data used in this indicator were collected without a standardised survey design (van Strien et al., 2013; Isaac et al., 2014a and b). For each species, records were extracted at the one kilometre 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 1970 was set to 100. The annual index 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 95% credible intervals. See the technical background document for further detail on production of the indicator.
A hierarchical, state-space model based on species annual growth rates was used to estimate the multispecies indicator (Freeman et al. 2020). The hierarchical structure allows estimation of uncertainty from different sources including that associated with the underlying species-specific index values and from having an incomplete set of trends for priority species with which to estimate the indicator. A smoothing process reduces the impact of between-year fluctuations - such as those caused by variation in weather - making underlying trends easier to detect. The resulting index is an estimate, with uncertainty, of the geometric mean occupancy. It is set to a value of 100 in the initial year. Changes subsequent to this baseline reflect the average percentage change in species occupancy; if on average species’ trends doubled, the indicator would rise to 200, if they halved it would fall to a value of 50.
Species were grouped into one of five categories based on both their short-term (over the most recent five years of data) and long-term (all years) mean annual change in occupancy. The threshold values for each category were based on those of the wild bird indicator. See the technical background document on the Bayesian indicator development for further detail on the calculation of the species-specific trends.
The trends of the taxonomic groups included within a multi-species indicator are often obscured by its composite nature. Indicator lines have been generated for a number of sub-groups using the same method so that the trends for these groups can be seen more clearly (see Figure C4bii). The bees, wasps and ants group experienced an overall decline, with an index value in 2018, 87% of that in 1980. These are counterbalanced by increases in bryophytes and lichens, which had an index value of 161 in 2015. The moths have undergone the biggest decline with an index value in the final year 68% of the value in 1970. Similar strong declines in moths were noted in C4a. The underpinning causes of this decrease are not completely understood.
Since 2020, data updates to the Biological Records Centre database were received for five taxonomic groups: Aquatic bugs, Empid & Dolichopodid Flies, Ephemeroptera, Plecoptera and Trichoptera.
Figure C4bii. Change in distribution of priority species, by taxonomic group, 1970 to 2018
Notes about Figure C4bii:
- The graphs show the smoothed trend (solid line) and variation around the line (shaded area) within which users can be 95% confident that the true value lies (credible interval) for each of the taxonomic groups included in the composite indicator.
- The figures in brackets show the number of species included in each measure.
- Other taxa includes a number of insect groups, molluscs and spiders.
- All species in the indicator are present on one or more of the country priority species lists (Natural Environmental and Rural Communities Act 2006 – Section 41 (England), Environment (Wales) Act 2016 section 7, Northern Ireland Priority Species list, Scottish Biodiversity List).
- The indicator for bees, wasps and ants starts in 1980.
- These charts are not directly comparable to previous versions of the indicator. Inclusion of new data has increased the number of species that can be included in the indicator from 422 in 2020, to 476 this year. Additionally, novel methods to exclude species and to combine individual species trends into the multi-species indicator have been applied in 2021.
Source: Biological records data collated by a range of national schemes and local data centres.
Goals and Targets
The UK and England Biodiversity Indicators are currently being assessed alongside the Environment Improvement Plan Targets, and the new Kunming-Montreal Global Biodiversity Framework Targets, when this work has been completed the references to Biodiversity 2020 and the Aichi Global Biodiversity Framework Targets will be updated.
Aichi Targets for which this is a primary indicator
Strategic Goal C. To improve the status of biodiversity by safeguarding ecosystems, species and genetic diversity.
Target 12: By 2020, the extinction of known threatened species has been prevented and their conservation status, particularly of those most in decline, has been improved and sustained.
Aichi Targets for which this is a relevant indicator
Strategic Goal B. Reduce the direct pressures on biodiversity and promote sustainable use.
Target 5: By 2020, the rate of loss of all natural habitats, including forests, is at least halved and where feasible brought close to zero, and degradation and fragmentation is significantly reduced.
Strategic Goal C. To improve the status of biodiversity by safeguarding ecosystems, species and genetic diversity.
Target 11: By 2020, at least 17 per cent of terrestrial and inland water, and 10 per cent of coastal and marine areas, especially areas of particular importance for biodiversity and ecosystem services, are conserved through effectively and equitably managed, ecologically representative and well connected systems of protected areas and other effective area-based conservation measures, and integrated into the wider landscape and seascapes.
Web links for further information
- Aquatic Heteroptera Recording Scheme Home page
- British Arachnological Society Spider Recording Scheme Home page
- Bees, Wasps and Ants Recording Society Identification guides to download
- British Bryological Society Home page
- Lacewings and Allies Recording Scheme Home page
- British Lichen Society Home page
- British Dragonfly Society Recording Dragonflies and Damselflies in the British Isles
- British Myriapod and Isopod Group Centipede and Millipede Recording Schemes
- Bruchidae & Chrysomelidae Recording Scheme Relevant BRC webpage
- Butterfly Conservation Butterflies and Moths
- UK Centre for Ecology & Hydrology – Biological Records Centre Home page
- UK Centre for Ecology & Hydrology – Biological Records Centre Recording Schemes
- Conchological Society of Great Britain and Ireland Home page
- Diperists Forum Cranefly, Empididae & Dolichopodidae, Fungus gnat Recording Schemes
- Gelechiid Recording Scheme Home page
- Ground Beetle Recording Scheme Home page
- Hoverfly Recording Scheme Home page
- National Moth Recording Scheme Home page
- Orthoptera Recording Scheme Home page
- Riverfly Recording Schemes: Ephemeroptera, Plecoptera and Trichoptera Home page
- Soldierflies and Allies Recording Scheme Home page
- Staphylinidae Recording Scheme Relevant BRC webpage
- Terrestrial Heteroptera Recording Scheme - Shield bugs and allied species Home page
- UK Beetle Recording Weevil and Bark Beetle Recording Schemes
- UK Biodiversity Partnership UK Biodiversity Action Plans
- NatureScot Scottish Biodiversity List
- Wales Biodiversity Partnership Section 7 priority species in Wales
- Natural England S41 List of priority species in England
- Northern Ireland Environment Agency Northern Ireland Priority Species List
References
Eaton, M. A., Burns, F., Isaac, N. J. B., Gregory, R. D., August, T. A., Barlow, K. E., … Williams, J. (2015). The priority species indicator: measuring the trends in threatened species in the UK. Biodiversity, 16(2 to 3), 108 to 119. https://doi.org/10.1080/14888386.2015.1068222
Freeman, S.N., Isaac, N.J.B., Besbeas, P. et al. A Generic Method for Estimating and Smoothing Multispecies Biodiversity Indicators Using Intermittent Data. JABES 26, 71 to 89 (2021). https://doi.org/10.1007/s13253-020-00410-6
Isaac, N. J. B., August, T. A., Harrower, C. and Roy, D. B. (2013). Trends in the Distribution of UK native species 1970 to 2010. Preliminary report to JNCC. JNCC Report No 488.
Isaac, N. J. B., van Strien, A. J., August, T. A., de Zeeuw, M. P. and Roy, D. B. (2014a). Statistics for citizen science: extracting signals of change from noisy ecological data. Methods in Ecology and Evolution, 5(10), 1052 to 1060. https://doi.org/10.1111/2041-210X.12254
Isaac, N. J. B., van Strien, A. J., August, T. A., de Zeeuw, M. P. and Roy, D. B. (2014b). Extracting robust trends in species’ distributions from unstructured opportunistic data: a comparison of methods. BioRXiv. https://doi.org/10.1101/006999
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(6), 1450 to 1458. https://doi.org/10.1111/1365-2664.12158
Downloads
Download the Datasheet and Technical background document from JNCC's Resource Hub.
Last updated: October 2021
Latest data:
Distribution data – 2018
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