Red List Index (RLI)

The Red List Index (RLI) shows trends in overall extinction risk for species, and is used by governments to track their progress towards targets for reducing biodiversity loss.

 

Most species that move between categories on The IUCN Red List (see the section Reasons for Changing Category) do so because of improved knowledge or revised taxonomy. It is therefore impossible to determine any meaningful trends in the status of biodiversity simply by looking at overall changes in numbers of threatened species between updates. For this reason, the figures presented in the Summary Statistics for numbers of threatened species in each IUCN Red List since 1996 must be interpreted with extreme care; these figures illustrate increasing assessment efforts by IUCN and its Partners since 1996, helping to refine our current understanding of the status of biodiversity, rather than showing genuine status changes over time.

To address this, the Red List Index (RLI) has been developed, which shows trends in the status of groups of species based only on genuine improvements or deteriorations in status of sufficient magnitude to qualify species for listing in more threatened or less threatened Red List Categories. 

Currently, the RLI is available for five taxonomic groups only (those in which all species have been assessed at least twice): birds, mammals, amphibians, cycads and warm-water reef-forming corals (see Figure 1). It has also been aggregated into a single index for those five groups (see Butchart et al. 2010 for methodology). The RLI clearly demonstrates that the status of these major groups is still declining. 

The RLI can be disaggregated in various ways: thematic RLIs show trends for subsets of species of particular policy relevance. For example, the RLI for pollinator species shows trends in the status of species that are particularly important for the role they play in plant pollination, while the RLI for forest-specialist species (Figure 2) is an indicator of the balance between loss and degradation of the world's forests and efforts to conserve and restore them. Other thematic RLIs show trends for all species (in the groups for which repeated Red List assessments have been carried out) driven by particular factors, such as invasive alien species, to illustrate the balance between the negative impacts and spread of such species, and the efforts to control or eradicate them.