1. Indicator Name
The proportion of populations within species with an effective population size > 500
This is sometimes referred to as “the Ne 500 indicator” or “genetic diversity within populations indicator” or
“Effective population size 500 indicator”
3. Goals And Targets Addressed
Goal A The integrity, connectivity and resilience of all ecosystems are maintained, enhanced, or restored,
substantially increasing the area of natural ecosystems by 2050; Human induced extinction of known threatened species
is halted, and, by 2050, the extinction rate and risk of all species are reduced tenfold and the abundance of native
wild species is increased to healthy and resilient levels; The genetic diversity within populations of wild and
domesticated species, is maintained, safeguarding their adaptive potential.
Headline indicator for Target 4.Ensure urgent management actions to halt human induced extinction of known threatened
species and for the recovery and conservation of species, in particular threatened species, to significantly reduce
extinction risk, as well as to maintain and restore the genetic diversity within and between populations of native,
wild and domesticated species to maintain their adaptive potential, including through in situ and ex situ conservation
and sustainable management practices, and effectively manage human-wildlife interactions to minimize human-wildlife
conflict for coexistence.
That being said, as noted by Hoban et al 2023a, and
explained below, it is also relevant to Targets 1, 3, 5, 9, and 12.
Effective population size (Ne) is a well-accepted metric for measuring the rate of loss of genetic diversity
within populations. As explained below, an Ne above 500 (usually a census population size of 5000) will
maintain genetic diversity within populations. 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 also vital for the success of ecosystem restoration and the (re)introduction of
populations and species. Populations with low genetic diversity suffer inbreeding, low viability, and low resilience.
Therefore, an Ne indicator is necessary to measure the conservation and sustainable use of genetic diversity.
Genetic diversity is variation at the DNA level, including differences among individuals within populations of
species and differences among populations of each species. However, assessing DNA with genetic sequencing
technology can be time consuming, and requires substantial funds, skills and technology, making it challenging for
large-scale evaluation, particularly in species-rich nations.
Fortunately, we can assess genetic status of species and populations via Ne without needing DNA data.
This is important since relatively few species have DNA-based studies, especially in biodiversity hotspots.
In 2020, three genetic diversity indicators were proposed, including the Ne 500 indicator. They have the following
- are scientifically valid, based in core conservation and genetic concepts
- are affordable and feasible with existing data
- require a moderate to low time and resource investment
- leverage diverse data and multiple ways of knowing including local knowledge holders
- can often align with other biodiversity assessments
- allow for easy translation into policy and management of species
- are applicable and relevant in all countries, taxonomic groups, and ecosystems.
- use concepts that are intuitive or accessible to non-geneticists (e.g. genetic losses due to
small populations and loss of populations).
- are ‘forward compatible’, meaning they can incorporate new methods that arise
What is the Effective Population Size (Ne) 500 indicator?This indicator is based on the knowledge
that populations that are small in size (effective population size (Ne) < 500) are highly susceptible to rapid loss
of genetic diversity and are at high risk of extinction due to genetic threats. As shown in the figure, Ne 500
is widely recognized by scientists and conservation practitioners as a “sufficient” size to prevent loss of genetic
diversity within populations (in this case, a statistic called ‘heterozygosity’) – Ne much higher than Ne
500 and genetic loss within populations is near zero. Much lower and genetic loss becomes rapid.
And Ne can be measured without DNA data. Ne can be approximated from population census
size. Typically, Ne is about 0.1 of the census size. As Hoban
et al (2023b) and Hoban et al
(2020) show, there are many sources of census size data which countries can employ, and indeed can leverage
existing in-country data, expertise, and biodiversity infrastructure.
The Ne 500 indicator is likely the best evidence of genetic status and risk of genetic erosion when DNA sequencing is
not available (the case for most species globally). This indicator provides a measure of the loss or maintenance of
genetic diversity within populations and is feasible and scalable for many species per country. Maintaining effective
sizes above 500 will protect the genetic diversity within populations for many generations.
Illustration of loss of genetic diversity when Ne <500. Adapted from Willi et al, Dec 2021 PNAS.
Thus, this indicator is directly relevant to Goal A, as it informs the health and resilience of
species’ populations, their genetic diversity, and the threat of species extinction. Knowledge of species population’s
effective size is relevant to Target 4 as it facilitates active management of species, ex situ
breeding programs and informs the conservation efforts and recovery process of species populations following
environmental disruption. The Ne 500 indicator is Headline indicator for Goal A and Target 4. As noted by Hoban et al (2023a), the Ne 500 indicator is relevant to other
targets such as sustainable harvest Targets 5 and 9 because harvested populations should be
maintained at Ne 500. To ensure all genetically distinct populations are represented at sufficient sizes to maintain
their persistence, it is relevant for Targets 1 and 3 on biodiversity inclusive spatial planning and
representative protected areas, respectively, and Target 12 for increasing area and connectivity of
green and blue spaces in urban environments to promote gene flow and species recovery.
The indicator is complementary to, and can be reported in, a wider genetic scorecard (O’Brien et al. 2022), as
well as contribute to the refinement of other indicators or initiatives (e.g., identifying Key Biodiversity Areas to
inform spatial planning, assessing protection level of species).Note that the Ne 500 indicator is relevant for genetic
diversity within populations and a separate indicator (i.e. complementary indicator for Goal A on the “proportion of
populations maintained”) is necessary for maintaining genetic diversity among populations. Experts agree that
both indicators are critical for assessing and monitoring the genetic health of species.
5. Definitions Concepts And Classifications
The indicator definition is exemplified in the full name, “The proportion of populations within species with a
genetically effective population size > 500.”The indicator should be reported for 100+ representative species per
country.It is calculated by taking each population of a species, determining if each population is above the threshold
of Ne 500, calculating a proportion of populations above the threshold for each species, and then taking a mean of
these proportions across all species examined, as explained in Hoban et
al (2023b).As explained in that publication which contains the basic equations for calculation, the indicator
can be weighted by taxonomic groups or other categories to offset any biases in the species selected (e.g. due to
having more birds, more rare species etc.). IUCN has published guidance on selecting species and populations for
monitoring of genetic diversity (Hvilsom
et al. 2022).
Other important definitions:
The effective population size (Ne) is a way to quantify the rate of genetic
change, or genetic erosion. Effective population size of a population is related to the number of adult/ breeding
individuals in a population that contribute offspring to the next generation, the relative evenness of their offspring
production, sex ratio, and other factors. The current state of Ne has important meaning for genetic
biodiversity as it represents ongoing genetic erosion. Any population with Ne below 500 is likely
losing genetic diversity fairly quickly, and signals ongoing loss of genetic diversity.
The effective population size may be a fraction (e.g., 10%) of the species census population size
(Nc), which is the number of adult individuals present in a discrete area. As noted
below, a fraction of 1/10th is widely recognized as a slightly conservative ratio between Ne:Nc. When knowledge exists
for a certain taxonomic group, an alternate fraction may be used.
To maintain genetic diversity typically means that the amount of genetic diversity (alleles,
heterozygosity) does not decrease, and there is no loss of within-population genetic diversity or among population
genetic diversity; the precise genetic composition may shift for adapting to environmental change. The
Ne 500 indicator ensures maintenance of within-population genetic diversity. We note that some
scientists have argued for a more conservative minimum Ne of 1000, though the Ne 500 recommendation remains common.
To safeguard genetic diversity typically means to protect genetic diversity e.g. with in situ and ex
situ protective measures (e.g. seed banks and botanic gardens, well managed protected areas, translocations, etc.)
5b. Method Of Computation
Effective population size (Ne) can be calculated for most species through a simple mathematical
transformation of the population's census size (Nc). Following the widely accepted rule of thumb of
1:10 effective-to-census size ratio, the default is multiplication of Nc by 0.1 (Hoban et al. 2020). For example, this
would equate to a census size of 5000 having an effective size of 500. However, for some taxonomic groups, a more
refined ratio could be employed (see Step 2 below).
Step 1: Define population boundaries and compile data on census size (Nc). For
each focal species it is first necessary to define ‘populations’ and to collect data on census population sizes. Many
local and national biodiversity monitoring programs (e.g. at species or ecosystem level) have already defined
populations based on geographic isolation, occupying distinct habitats or ecoregions, association with a geographic
feature like a mountain range or lake, etc. Full guidance on defining populations for a wide variety of organisms are
provided in the guidance manual for this indicator (Hoban et al
(2023b) and Supporting Information therein). After defining populations, it is necessary to collect data on
census population sizes (or to use genetic data). Again, many biodiversity monitoring programs for priority species
will have this data available - in some cases in a centralized national database, while in other cases, it may be
scattered among different national reports and assessments.A
recent webinar hosted by the CBD Secretariat and GEO BON showcased the different resources available to
countries, emphasizing the flexibility of this indicator.
Step 2: Calculate each population’s Ne. This entails first choosing a ratio of
effective-to-census size and multiplying the population’s census size by this ratio to obtain the population’s
effective size. As mentioned above, the default ratio, which is slightly conservative, is 1:10 or 0.1. Alternatively,
a taxon-specific ratio can be obtained in one of several ways: (a) from recent reviews of the literature that have
compiled average values for groups such as mammals, bony fish, annual plants, trees, etc. (see Hoban et al 2021), (b) from
formulas that take into account a species’ biological characteristics (especially the male-female sex ratio and the
variance in offspring production), or (c) from published literature on the species or even populations that are the
focus of study. For instance, the ratio in large-bodied mammals and in some trees is often closer to 0.3. These are
all valid ways of obtaining the ratio. To incorporate uncertainty in calculations, the calculation can be repeated
using multiple Ne/Nc ratios.But it is entirely acceptable and useful to use the
well-recognized 0.1 ratio.
Step 3: Calculate the proportion of populations above the 500 Ne
threshold. For each species, count the number of populations with Ne above 500 and
the number with Ne below 500; these two added together should equal the total number of populations.
The indicator can be reported as a proportion (from 0 to 1) of all populations that are above 500, or in the form of a
ratio ‘number of populations above 500’:‘total number of populations.’ (Recently extinct populations would have a size
of 0 to avoid an increase in the indicator value when populations are lost). To combine across species in a given
country or geographic location, a simple average of the proportion from Step 3 for all the relevant species should be
performed. If taxonomic groups are not represented evenly, the indicator value is the mean of each taxonomic group’s
means, which down-weights overly represented taxonomic groups, e.g. mammals. Additionally, each species can be
weighted by the proportion of its geographic range in the country, from 0 to 1, to reflect national responsibility,
with full weight for endemic species. Transboundary/ transnational populations can be weighted similarly (e.g. by the
proportion of that population falling within the Parties borders). The indicator would range between 0 and 1 (with 1
being the desired state - all populations above an effective size of 500).
Equations for indicator calculation are given in Hoban et al
Step 4: Temporal change in the indicator can be calculated using multiple time point values
of population size. Temporal increases in the proportion of populations with Ne
above 500 would indicate improvement in the maintenance of genetic diversity (on average slowing the rate of
genetic erosion and eventually ‘bending the curve’ such that genetic diversity is restored via natural processes of
mutation, migration, etc.). Decreases would indicate worsening (accelerating rate of genetic erosion), and static
values would indicate a stable state of the indicator (stable rate of genetic erosion - though not necessarily a
halting of genetic erosion - it is only halted when Ne >500).The indicator is designed to be
recalculated as new data are compiled, which in many species is a timescale of 2 to 5 years, thus the indicator would
be calculated and reported on typically once every 4 years (fitting the timespan of CBD reporting).
5c. Data Collection Method
In most cases, the indicator will be calculated using a transformation of census size (Nc), though
analysis of DNA data can also be used to obtain Ne and assess if Ne >500. The draft guidance manual (see Hoban et al (2023b) and Supporting Information therein) details other
methods of calculating the indicator when other data are available. The census size of local populations of target
species can be obtained from a variety of sources, including national biodiversity monitoring databases and programs,
endangered species management and recovery plans, detailed population information contained in some Red List
assessments, and expert consultation. Detailed guidance on these calculations and a variety of example calculations is
available now and will be revised following input from Parties as more Parties undertake this indicator.Demonstrations
of the data collection can also be seen in a recent CBD
The full data collection form can be found online here: https://ee.kobotoolbox.org/preview/2KDHEWrb. We have created
an online data collection form using Kobotoolbox (www.kobotoolbox.org/) and a guidance document (Supporting
Information) for anyone to use. Kobo is a free and flexible data collection tool commonly used in social,
environmental and epidemiological research.The data form adapts to the type of fundamental source data available and
can accommodate qualitative and quantitative data and different levels of certainty.By sharing these on github we are
promoting interactive engagement with stakeholders who can offer suggestions or ask questions, and removing paywalls
that might otherwise limit participation globally.
5d. Accessibility Of Methodology
Parties can directly calculate country-level values of this indicator by leveraging national data, expertise and
biodiversity assessments, and by following the guidance manual that is being developed by the GEO BON Genetic
Composition Working Group, in collaboration with conservationists globally. The method has been peer reviewed in
several publications (see list of References below, or https://www.coalitionforconservationgenetics.org/publications),
and a detailed methodology has been made available (see Supporting Information for Hoban et al. 2023b)
5e. Data Sources
As explained in Hoban et al (2023b) the indicator is flexible and
adaptable to the data sources already existing in each country.Examples from different countries illustrate the
diverse options available. Recovery plans for dozens to thousands of threatened species are mandated by national
legislation (Australia- the Environment Protection and Biodiversity Conservation Act,
https://www.dcceew.gov.au/environment/epbc; South Africa- Biodiversity Management Plans,
https://www.dffe.gov.za/content/management_plans/biodiversity; USA- the Endangered Species Act,
https://www.fws.gov/law/endangered-species-act). These documents typically detail species biology and demographic
status. In Japan, many threatened vascular plants have been surveyed for census size for over two decades by the
Japanese Society for Plant Taxonomy, while for common trees, statistical estimates for population size were estimated
from vegetation survey data. In Mexico, taxonomic experts who recently helped validate distribution models for crop
wild relatives will be consulted for indicator values. In France, Belgium, UK and Sweden, much biodiversity data from
experts, local knowledge holders, and diverse sources are collected in easy to access web-based portals (France- INPN,
Belgium - www.observations.be, UK- https://nbnatlas.org/, Sweden- Swedish Species Information Centre, Artdatabanken).
In Colombia, the Biodiversity Information System (SIB) repository compiles species surveys from throughout the country
(https://biodiversidad.co/), which is mandated by many public and private organizations. These data are reviewed by
national experts for validation and used to create freely available species distribution models
(http://biomodelos.humboldt.org.co/), and for conservation prioritization.
GEO BON, through its working groups, and national and thematic Biodiversity Observation Networks, is able to provide
capacity support, training and consultation. Considering that currently the workflow is manual rather than fully
automated, the indicator would be calculated for a relatively small number of representative species per country. This
may range from dozens on the low end to 1000 or more on the high end, but for many countries will be on the scale of
100 species. As noted above, data sources include national biodiversity monitoring databases and programs, endangered
species management and recovery plans, detailed population information contained in some Red List assessments, and
expert consultation. Detailed guidance on these calculations and a variety of example calculations is now available
5f. Availability And Release Calendar
Ready for deployment and updated every approximately four years.First draft of the guidance manual is available now
and an indicator is being calculated, see Hoban et al (2023b) .
5g. Time Series
Dependent on data quality at the national scale. Typically Nc will be obtained from the past decade
e.g. post 2010.Going forward it will be reported every 2 to 5 years, typically every 4 years, making it suited to the
CBD reporting schedule. As the indicator is increasingly deployed, indicator calculation can be made in temporal
windows, including through the use of older biodiversity observation data, reports and consultation with knowledge
holders, likely extending indicator assessment at least back to the 1990s.
5h. Data Providers
The data are sourced from in-country existing biodiversity and environment agencies, thus leveraging in-country
resources and ongoing programs. Other data may be obtained from conservation organizations, scientific societies,
national and public repositories (e.g., Global Biodiversity Information Facility, GBIF, Red List assessments), citizen
scientists, and the contributions of local and indigenous peoples and traditional knowledge holders.
5i. Data Compilers
The following organizations are responsible for maintenance of the methodology and tools for use: GEO BON, The Morton
Arboretum, Stockholm University, GBIKE, Coalition for Conservation Genetics. Actual compilation of data is performed
by in-country agencies
5j. Gaps In Data Coverage
Expected taxonomic gaps include cryptic (e.g. elusive, located underground, etc.) species, micro-organisms, fungi,
invertebrates. However, current projects deploying the indicator have shown it can be calculated for cryptic species
and invertebrates. Expected thematic and geographic gaps include species from understudied realms and areas (e.g.,
deep sea, mountains, and islands). These gaps are unfortunately typical for other biodiversity indicators such as the
Red List Index.
However, the indicator can be calculated at the population level or species level in any species, and thus has no
theoretical gaps, and (weighted) averages can be calculated across populations or species taking into account range
Note that the Ne 500 indicator should be complemented with the “proportion of populations maintained” indicator , and
with expert and local knowledge including as compiled in the “genetic scorecard for wild species” indicator , the
“comprehensiveness indicator” (all three suggested as complementary indicators for Goal A: CBD/COP/15/L.26),
and the proposed indicator “number of species and populations in which DNA based monitoring is used” (Hoban et al. 2020).
5k. Treatment Of Missing Values
Species with missing data may be aggregated with taxonomically-related species, or species with similar
characteristics and life history traits.Populations with missing data can be treated as NAs in the dataset.
6a. Scale Of Use
Scale of application (please check all relevant boxes): Global, Regional, National
Scale of data disaggregation/aggregation:
Global/ regional scale indicator can be disaggregated to national level:
National data is collated to form global indicator: Yes
6b. National Regional Indicator Production
The guidance documents currently developed explain national methodology. Underlying data will be accessible and
usable by countries. The existing data collection tool allows easy organization and storage of data and thus tracking
Countries can collaborate on transnational calculations if desired, and the same is true for regions, including the
European Union, for example.Otherwise regional calculation is a mean or weighted mean of component countries.
6c. Sources Of Differences Between Global And National Figures
The guidance document explains national methodology. The global figure is a mean, or weighted mean, of all
6d. Regional And Global Estimates And Data Collection For Global Monitoring
6d.1 Description Of The Methodology
Methods and mathematical formulas for aggregating at these scales, and for weighting countries are described in Hoban et al (2023b).
6d.2 Additional Methodological Details
See previous answer
6d.3 Description Of The Mechanism For Collecting Data From Countries
As noted above, national agencies, or conservation organizations can compile the indicator at national levels using
the resources provided in Hoban et al (2023b; see Supporting
Information).Consultation and questions about data validation can be made to the custodians of the indicator
(GEO BON, Morton Arboretum, Stockholm University, GBIKE, and Coalition for Conservation Genetics).
Species, taxa, rarity categories, habitat type, guilds.
9. Related Goals Targets And Indicators
Goal A. The genetic diversity within populations of wild and domesticated species, is maintained, safeguarding their
Target 4. Ensure urgent management actions to halt human induced extinction of known threatened species and for the
recovery and conservation of species, in particular threatened species, to significantly reduce extinction risk, as
well as to maintain and restore the genetic diversity within and between populations of native, wild and domesticated
species to maintain their adaptive potential, including through in situ and ex situ conservation and sustainable
management practices, and effectively manage human-wildlife interactions to minimize human-wildlife conflict for
That being said, as noted by Hoban et al 2023a, it is also relevant
to Targets 1, 3, 5, 9, and 12.
Linked to and is complemented by other important genetic diversity indicators (CBD/COP/15/5), including:
- Proportion of populations maintained within species
- Genetic diversity scorecard for wild species (O’Brien et al. 2022)
- Comprehensiveness of conservation of socioeconomically as well as culturally valuable species(Khoury et al 2019),
- Proportion of local breeds classified as being at risk, extinction
- Number of plant and animal genetic resources for food and agriculture secured in either medium- or long-term
Relevant background. Hoban et al (2023a). Genetic diversity Goals and Targets have improved, but
remain insufficient. Conservation Genetics 24, 181–191.. https://doi.org/10.1007/s10592-022-01492-0
Description of indicator deployment. Hoban et al (2023b). Monitoring status and trends in genetic
diversity for the Convention on Biological Diversity: an ongoing assessment of genetic indicators in nine countries.
Conservation Letters 00, e12953. https://doi.org/10.1111/conl.12953
Relevant background. Frankham, R. (1995). Effective population size/adult population size ratios in
wildlife: a review. Genetic Research, 66, 95–107.
Resources and guidance, description of methods for indicator deployment. Supporting Information
for:Hoban et al. (2023b) Monitoring status and trends in genetic diversity for the Convention on Biological Diversity:
an ongoing assessment of genetic indicators in nine countries. Conservation Letters 00, e12953. https://doi.org/10.1111/conl.12953
Description of the indicator. Hoban, S., Bruford, M., D’Urban Jackson, J., Lopes-Fernandes, M.,
Heuertz, M., Hohenlohe, P.A., et al. (2020). Genetic diversity targets and indicators in the CBD post-2020 Global
Biodiversity Framework must be improved. Biological Conservation, 248, 108654. https://doi.org/10.1016/j.biocon.2020.108654
Description of the indicator. Hoban, S., Paz-Vinas, I., Aitken, S., Bertola, L., Breed, M.F.,
Bruford, M., Funk, C., Grueber, C., Heuertz, M., Hohenlohe, P., Hunter, M., et al. (2021). Effective population size
remains a suitable, pragmatic indicator of genetic diversity for all species, including forest trees. Biological
Conservation, 253, 108906.
Relevant background. Hoban, S., Bruford, M., Funk, W.C., Galbusera, P., Griffith, M.P., Grueber,
C.E., Heuertz, M., Hunter, M.E., Hvilsom, C., Kalamujic, S.B., Kershaw, F., et al. (2021). Global commitments to
conserving and monitoring genetic diversity are now necessary and feasible. BioScience, 71, 964–976.
Relevant background. Laikre, L., Hohenlohe, P.A., Allendorf, F.W., Bertola, L.D., Breed, M.F.,
Bruford, M.W., Funk, W.C., Gajardo, G., González-Rodríguez, A., Grueber, C.E., Hedrick, P.W., et al. (2021). Authors’
Reply to Letter to the Editor: Continued improvement to genetic diversity indicator for CBD. Conservation
Genetics,22, 533–536. https://doi.org/10.1007/s10592-021-01359-w
Relevant background. Laikre, L., Nilsson, T., Primmer, C.R., Ryman, N. and Allendorf, F.W. (2009).
Importance of genetics in the interpretation of favourable conservation status. Conservation Biology,
12. Graphs And Diagrams
Figure 1. Example of the three genetic diversity indicators, for four hypothetical populations in Illinois, USA. One
tree = 1,000 plants (five trees = 5,000 plants). Colors illustrate genetic variation within and among populations. In
2020, 2 of 3 extant populations are Nc<5,000 (Ne<500 considering an
effective to census size ratio of Ne/Nc = 0.1) and thus too small to maintain genetic
diversity (indicator 1). Three of four historic populations are maintained (indicator 2). DNA-based methods have been
used to monitor genetic diversity in two populations (indicator 3 - a value of 1 means that one or more populations of
the species is monitored with DNA-based methods).
Figure 2: Pictorial representation of
how genetic diversity is found within and among populations (see color variations) and is the foundations for
species adaptability and for entire ecosystems. Genetic diversity ultimately is seen at the DNA level, and can be
conserved with large (Ne ⩾500) populations and by making sure distinct populations are not
Figure 3: Pictorial representation of
Ne relative to the census size of a population. Ne is smaller than
Nc, but it is the Ne which determines the rate of loss of genetic
diversity within populations, and thus whether they can maintain adaptive capacity.