Which taxa to include?


In many cases, which species to include in the Red List exercise will be defined by the project scope (i.e. focus on specific taxa – a Red List of Vertebrates – or a single taxon – a Red List of Freshwater Molluscs). Which species to include also has a direct bearing on the usefulness of the resulting data (e.g. comprehensive assessments versus selection of threatened species only). For example, some projects draft a species list based on perceived rarity and threat, thus only including potentially threatened species in the assessment.

However, to have the maximum benefit from carrying out a Red List assessment, it is advisable to cover biodiversity more broadly, ideally including a variety of comprehensively-assessed species groups (so also including those species not deemed at risk of extinction). If funding is limited, selecting species groups which can act as an indicator for other taxa and comprehensively assessing those can provide a good first step.


Threatened taxa only versus comprehensive assessments

Pre-selecting a species list made up of potentially rare and threatened species might streamline and speed up the assessment process while still allowing the resulting data to be used for conservation planning, albeit based on a subjective and biased set of species. However, this approach is not recommended since it creates a biased dataset, prevents data synthesis on other parts of biodiversity (such as common species which may also be in decline, although this might be less noticeable at present), and prevents the use of Red List data as a Red List indicator. In addition, only through the assessment process can species be identified as threatened or not, hence species previously thought at low risk of extinction may fall within threatened categories following the assessment, and vice versa, species thought to be threatened may in fact be at a low risk of extinction.


A broad view of biodiversity allows more comprehensive conservation planning

More often than not, the level of threat in one species group is not a particularly good indicator of the level of threat in another, and this is particularly true when comparing species groups occupying different systems (i.e. terrestrial versus freshwater (e.g. Collen et al. 2012). At the global level, for example, there has been a real push to broaden the coverage of Red List assessments to boost the number of invertebrate, plant and fungi assessments on the IUCN Red List (e.g. the sampled approach to Red Listing and the IUCN Freshwater Biodiversity assessment).

For example, a recent analysis of taxonomic coverage of National Red Lists showed that plants were most widely assessed (Zamin et al. 2010, see research papers in our library). However, many countries have a much wider taxonomic coverage, for example Mongolia now has produced National Red Lists for all vertebrates, while Switzerland has produced Red Lists for 27 organism groups, including invertebrates, plants, lichen and fungi.

Carrying out assessments for species in certain systems, for example freshwater, leads to better representation of freshwater biodiversity in conservation planning. In other countries or regions, functional groups providing a particular service have been assessed, such as saproxylic beetles in Europe.


Using the IUCN Categories: Not Applicable species

The first step of any national- or regional-level assessment is to decide the species list which is to be assessed. This means that those species not applicable to the assessment process have to be identified. The IUCN defines Not Applicable species as those taxa which are not eligible for a regional or national assessment, i.e. introduced taxa (not indigenous to the region and introduced for reasons other than conservation) or vagrant taxa (not indigenous to the region but occurring only occasionally and irregularly).

Taxa eligible for regional assessment are taxa that are native to the region:

  • Indigenous taxa breeding within the region.
  • Naturally re-colonizing taxa (formerly Regionally Extinct).
  • Reintroduced taxa (formerly Regionally Extinct).
  • Marginal taxa (small proportion of global range/population within the region).
  • Visiting non-breeding taxa (not breeding there, but using essential resources)

For marginal and visiting non-breeding taxa, it might be worthwhile to set a filter, i.e. a threshold to determine which taxa are included and which are Not Applicable (NA). This filter could for example be that species are Not Applicable if less than 1% of the global population is present or uses resources in the region. It is important that the filters applied to species are clearly stated in the Red List documentation for reasons of transparency, and that, if following the IUCN Categories and Criteria, these taxa are assessed as Not Applicable.

The Guidelines for application of IUCN Red List Criteria at regional and national levels contains a flowchart to help determine which species should be included in the assessment process (Figure 1).



Figure 1. Flowchart to determine which taxa to include in a regional Red List (Source: Guidelines for application of IUCN Red List Criteria at regional and national levels, Annex 3, IUCN)