The Sampled Red List Index

Butterflies - Kaeng Krachan National ParkThe conservation status of less than 2.5% of the world’s described biodiversity is currently known. Clearly this limits understanding of the impact of humans on biodiversity, and with it the ability to make informed decisions on conservation planning and action. One of the major challenges for The IUCN Red List is assessing the larger groups that represent the majority of the world’s biodiversity.

The Sampled Red List Index (SRLI) is a new initiative to broaden the taxonomic coverage of The IUCN Red List in order to better represent biodiversity, provide increased species data coverage, enable a better understanding of biodiversity status and trends, and to identify key regions and taxa that require greater conservation attention.

The Sampled Red List Index is an adaptation of the IUCN Red List Index (RLI), which is based on the IUCN Red List of Threatened Species and is an indicator of the relative rate at which the conservation status of certain species groups change over time.

The SRLI is a collaboration between IUCN members, coordinated through the Institute of Zoology. By conducting conservation assessments at regular intervals, changes in the threat status of taxonomic species groups can be used to monitor trends in extinction risk.

RLIs have already been calculated for birds (photo) and amphibians – two species groups which have been comprehensively covered in the IUCN Red List. The RLI has been adopted by the CBD as one of the indicators to measure progress towards this important target, and specifically to monitor changes in threat status of species.

Species coverage of the Sampled Red List Index

Biodiversity conservation has in the past mainly concentrated on charismatic megafauna, such as mammals and birds. The IUCN Red List now contains complete assessments for mammals, birds and amphibians - and reptile and fish assessments are well on the way, in part due to the SRLI project. But what about the majority of our biodiversity which is represented by invertebrates and plants?

The number of described species in lesser known groups, such as invertebrates and plants, still lags a long way behind the estimated global total species richness, and conservation status of these species groups is therefore largely unknown.

Many of these groups play vital roles in the functioning of our ecosystem and therefore to our own well-being.

One of the major conservation challenges lays in the assessment of the conservation status the larger groups that represent the majority of the world’s biodiversity, such as invertebrates and plants.

Broadening species coverage: the SRLI species groups

Work started in 2007 on the following species groups, helping to broaden IUCN Red List coverage by including large numbers of invertebrates in the assessment process:

  • Comprehensive assessments are complete for amphibians, birds, crayfish, freshwater crabs, lobsters, mammals and reef-building corals
  • Comprehensive assessments are underway for cephalopods
  • Sampled assessments are complete for dragonflies, fish and reptiles
  • Sampled assessments are underway for butterflies, dung beetles, freshwater molluscs, gymnosperms and monocotyledon plants

How did the SRLI come about?

In recognition that targets such as CBD 2010 require a more rapid approach to generating conservation assessments across mega-diverse taxonomic groups, a sampled approach to the Red List Index (SRLI) has been developed in order to determine the threat status and trends of lesser-known and less charismatic species groups.

The SRLI is based on a representative sample of 1,500 species selected for a number of taxonomic groups within vertebrates, invertebrates, plants, and fungi. Taxonomic groups consisting of less than 1,500 described species will be comprehensively assessed using the IUCN Red List Categories and Criteria.  As a result, the SRLI will provide a more broadly representative picture of biodiversity change.

It will give us baseline information on the current status of biodiversity, which we can compare to potential future changes in threat status during reassessments of the SRLI taxa.

Who carries out the assessments?

Any project as ambitious as this requires a large network of contributors. Different species groups are assessed by different organisations or initiatives. For example, comprehensive species assessments from the IUCN-led Global Mammal Assesment and Global Amphibian Assessment, as well as comprehensive bird assessments coordinated by Birdlife International, will feed into the SRLI.

Other species groups are being assessed by expert organisations: for example, plants are assessed at the Royal Botanical Gardens at Kew , corals by the Global Marine Species Assessment and dragonflies by the IUCN Dragonfly Specialist Group.

ZSL has led the SRLI assessments for a number of groups, such as crayfish, freshwater molluscs, reptiles, fish and lobsters.

IUCN Red List

How is the SRLI calculated?

In a nutshell, the SRLI uses weight scores based on the Red List status of each of the sample species. These scores range from 0 (Least Concern) to Extinct/Extinct in the Wild (5).

Summing these scores across all species and relating them to the worst-case scenario - where all species are extinct - gives us an indication of how biodiversity is doing. Repeating the assessments over time will then allow us to see whether the extinction risk of biodiversity is overall increasing, decreasing or staying the same.