Focal Area: Status and trends of the components of biodiversity

Headline Indicator: Change in status of threatened species

Key Indicator Partners:      

Associate Indicator Partner:

Data Available: Global time series, 1980 onwards (periods differing for different taxonomic groups)

Development Status: Ready for global use

Species and the ecosystems of which they are part provide a range of goods and services which support everyday life. This biodiversity is essential for livelihoods and the cultural integrity of people. Yet biodiversity is currently being lost at an alarming rate due to human activities. At present, species extinction rates exceed background rates by two to four orders of magnitude.

Species are the most intuitive unit of biodiversity, and one which resonates with the public and about which we have a relatively good understanding. The IUCN Red List is a well-established and respected system for classifying species by their relative risk of extinction. Tracking the net movement of species through the Red List categories provides a useful metric of changing biodiversity status.

The IUCN Red List Index (RLI) shows changes in the overall extinction risk of sets of species, with RLI values relating to the proportion of species expected to remain extant in the near future without additional conservation action. The RLI measures the overall rate at which species move through IUCN Red List categories towards or away from extinction. It is calculated from the number of species in each category (Least Concern, Near Threatened, Vulnerable, Endangered, Critically Endangered, Extinct), and the number changing categories between assessments as a result of genuine improvement or deterioration in status (category changes owing to improved knowledge or revised taxonomy are excluded). The RLI can be calculated for any set of species that has been assessed at least twice for the IUCN Red List. At present, RLIs are available for all birds, mammals, corals and amphibians (with the latter two based on preliminary data), and an RLI for cycads is due very soon.

One challenge in expanding the taxonomic coverage of the RLI is that repeated Red List assessments of all species in poorly known, species-rich groups (e.g. insects, fungi, plants, etc) would be extremely costly. As a result, a sampled approach to the Red List Index has been developed to provide a measure more taxonomically representative of the world’s biodiversity.

The RLI can be disaggregated to explore trends in the different biogeographic realms, ecosystems, and habitats, for suites of species relevant to different policy mechanisms (e.g. wetland-dependant species for the Ramsar Convention on Wetlands and migrants for the Convention on Migratory Species) and it can also be applied at the global, regional, and in some cases , national scales.

Red List Index for the world’s mammals, birds, amphibians and corals. 

Source: Hilton-Taylor et al. (2009).

An RLI value of 1.0 equates to all species being categorized as Least Concern, and hence that none are expected to go extinct in the near future. An RLI value of zero indicates that all species have gone Extinct. A downwards trend in the graph line (i.e. decreasing RLI values) means that the expected rate of species extinctions is increasing i.e. that the rate of biodiversity loss is increasing. A horizontal graph line (i.e. unchanging RLI values) means that the expected rate of species extinctions is unchanged. An upward trend in the graph line (i.e. increasing RLI values) means that there is a decrease in expected future rate of species extinctions (i.e. a reduction in the rate of biodiversity loss).

‘The RLI shows that all species groups with known trends are deteriorating in status, as more species move towards extinction than away from it. Amphibians are more threatened than birds and mammals, but corals are deteriorating in status fastest, owing to increased frequency of ‘bleaching events’ brought about by climate change. South-East Asia is the region in which mammals are most threatened and in which mammals and birds have deteriorated most dramatically. This is a consequence of the rapid rate of deforestation of the region’s Sundaic lowlands combined with unsustainable levels of hunting. Birds are most threatened in Oceania, where island species are often susceptible to invasive species that humans have deliberately or inadvertently introduced. The fungal disease chytridiomycosis is the major driver of declines in amphibians.’

National RLIs can be calculated either by disaggregating the global indices, or by repeatedly assessing extinction risk at the national scale. Examples of both approaches are currently being written up for publication. Many countries have compiled national red lists which form the basis of the latter approach (see www.nationalredlist.org), but so far few have done this twice or more using consistent methods. As they increasingly do so, however, many more national RLIs will become available.

More information about producing national RLIs can be found in the publication, IUCN Red List Index – Guidance for National and Regional Use, available from the 2010 BIP webpage for this indicator.

A method for calculating an aggregated RLI based on the data for multiple taxonomic groups is currently being written up for publication. RLIs for further taxonomic groups are in development. Representative samples of species have been assessed for reptiles, freshwater fish, dragonflies etc. and these (along with comprehensively assessed groups such as conifers and freshwater crabs) will be reassessed periodically in future. A method for calculating an aggregated RLI based on the data for multiple taxonomic groups is currently being written up for publication. RLIs for further taxonomic groups are in development. Representative samples of species have been assessed for reptiles, freshwater fish, dragonflies etc. and these (along with comprehensively assessed groups such as conifers and freshwater crabs) will be reassessed periodically in future.