Genetic diversity of wild species

Figure 1: Assessing genetic viability: Species-level proportion of populations above Ne 500

Figure 2: The frequency of species with proportions of populations above Ne 500

Relevance

Genetic diversity is necessary for species’ populations to remain healthy and adapt to environmental change, such as climate change, pollution, changing habitats, and pests and disease. Genetic diversity is also vital for resilience of all ecosystems, such as recovery from heat waves and ocean pollution or acidification. It is important for the success of ecosystem restoration and the reintroduction of populations and species. Populations with low genetic diversity suffer inbreeding, low viability, and low resilience. Habitat loss, fragmentation, overharvesting, and other human activities can all lead to declines in genetic diversity. Therefore, an Ne indicator is necessary to measure the conservation and sustainable use of genetic diversity.

International/domestic reporting

The suite of UK Biodiversity Indicators has been revised and updated to bring it in line with the Kunming-Montreal Global Biodiversity Framework (GBF) of the Convention on Biological Diversity (CBD). Some UK Biodiversity Indicators will be used for the forthcoming UK national reports to CBD.

This indicator relates to GBF Goal A: protect and restore; and Target 4: halt species extinction, protect genetic diversity, and manage human-wildlife conflicts.

Web links for further information

• Metadata factsheet for GBF Headline Indicator A.4
• Scottish Scorecard of Genetic Diversity in Wild Species
• Coalition for Conservation Genetics

Methodology

Available resources offering guidance on the production of this indicator, such as that published by the IUCN, suggest a wide range of potential criteria for species inclusion, including a broad range of taxonomic groups, ecosystem services, coverage across the 4 UK countries, representative national habitats, and a country-specific list of relevant criteria. A list of these criteria was created as follows:

• A range of taxonomic groups were included, covering all vertebrate orders, two invertebrate orders, flowering and non-flowering plants, and fungi. While not a formal taxonomic group, ‘Algae’ is a useful classification of species and is recommended for inclusion in future assessments. A taxonomic group level summary of results is in Table 2.
• Species from the 4 UK countries were included to ensure full representation; although in practice each country is represented by many species on the list.
• To ensure inclusion from all representative UK ecosystem types, Global Ecosystem Typology (GET) biomes were included as a criterion for species selection. Basing these criteria on GET ensures alignment across the Global Biodiversity Framework indicators, and it was decided to use GET level 2 biomes as GET level 3 would result in too many categories. Six GET level 2 biomes were excluded due to being of limited relevance to this indicator.
• The remaining criteria are largely as noted on pages 17 and 18 of the IUCN guidance on species selection for genetic indicators, with the exception of ‘Broad taxonomic spread’ as this is covered by the approach above. Included are a set of criteria based on urgent conservation and management issues, and another set more specific to the individual focus of the reporting country.

Subsequently, a total of 43 species were selected as collectively they represent the full range of criteria described above. The individual species were selected using a range of criteria:

• Royal Botanical Garden Edinburgh, NatureScot and the University of Edinburgh have developed Genetic Scorecards for assessing the genetic health of a broad indicative selection of Scottish species, and this work was expanded during 2025 to include an assessment of Nc and Ne for these species across the UK. Where possible, these species were re-assessed and included in this indicator; each species was assigned a line according to their relevance to the above criteria.
• For taxonomic groups not represented by a Genetic Scorecard, species were selected at random from an NBN Atlas species list for that group.
• For the 4 country criterion, only 2 countries remained as England and Scotland were already represented. For Northern Ireland, a random species was chosen (following the process outlined above) from the Northern Ireland Priority Species List; and for Wales a random species was chosen from the Section 7 species list for Wales.
• For the remaining GET level 2 biomes not represented, species lists were sourced from existing indicators such as Birds of the Wider Countryside, or JNCC biotype species lists. These lists were then randomised as above. In a small number of cases additional checks were carried out to ensure the species was suitable for the given criteria. If the species was not suitable, the list was randomised again and a new species chosen.
• Finally, species were selected to fulfil the ‘other’ criteria. In some cases, species lists were available for randomising (e.g. species for which tissue samples are available), but in other cases this approach was not possible and so a more subjective approach was required; for example the selection of red deer from the Genetic Scorecard list to meet the ‘populations subject to harvesting’ criteria.

For some species, higher and lower population bounds but no point estimates existed, and so an average of these was taken to create the Ne value. Due to limitations in data availability, some species initially selected following the above process were unable to be assessed; some species had no census details available, while for others a total species census was available but there were insufficient data to reliably apply a population structure and therefore the size of individual populations could not be assessed. However data were available for some additional species which were considered suitable for inclusion, to ensure a more robust sample size of species and taxa for the indicator. A full list of species included is in Table 1.

Expert elicitation was used to assess each species, to create estimates of the number of populations within the UK, and the size of each population. For each species, populations were defined using one of the following methods:

• Geographic boundaries
• Dispersal buffers
• Ecological or biogeographic proxies
• Traits, including behavioural (e.g. different breeding grounds), morphological, and physiological
• Genetic clusters or clades
• Evolutionarily Significant Units (ESUs)
• Management units

This process created estimates of Nc (census size) for each population within a species (Table 1), and therefore each was divided by 10, or a specific ratio where known, to create Ne, the effective population size. These data were then aggregated to calculate the overall indicator metric and taxonomic aggregations as above (Table 2). The overall value calculated was 0.64 (± 0.46).

Table 1: The proportion of populations within species with an effective population size greater than 500

Source: Genetics indicator working group (see Acknowledgements)

Notes about Table 1

• Only populations with census data available have been included in these calculations.

Table 2: The proportion of populations within taxa with an effective population size greater than 500

Source: Genetics indicator working group (see Acknowledgements)

Notes about Table 2

• This table summarises populations by taxonomic group.

Caveats and limitations

Due to limitations in data availability, Ne has been assessed for 43 species. While every effort has been made to ensure that these species are broadly representative of UK biodiversity, the indicator would benefit from the inclusion of a wider range of taxa. It is planned that future iterations of this indicator will be expanded to include new species as well as repeat assessments of the species already included.

Development plan

This is a new indicator. We plan to further develop the indicator during the coming years. We would like to include more species and a wider range of taxa in future iterations of the indicator.

We are keen to hear from our users about these intended changes, the language and visualisations used in this indicator, as well as our published development plan for the biodiversity indicators: please email us.