. Ecosystems and Human Well-Being: Biodiversity Synthesis . better 1988 1990 1992 1994 1996 1998 2000 2002 2004 The Red List Index illustrates the relative rate at which sets of species change in overall threat status (, projected relative extinction risk), based on population, range size, and trends as quantified by categories on the IUCN Red List. Between 12% and 52% of species within well-studied higher taxa are threatened with extinction, according to the IUCN Red List. Less than 10% of named species have been assessed in terms of their conservation status. Of those that have, birds ha
. Ecosystems and Human Well-Being: Biodiversity Synthesis . better 1988 1990 1992 1994 1996 1998 2000 2002 2004 The Red List Index illustrates the relative rate at which sets of species change in overall threat status (, projected relative extinction risk), based on population, range size, and trends as quantified by categories on the IUCN Red List. Between 12% and 52% of species within well-studied higher taxa are threatened with extinction, according to the IUCN Red List. Less than 10% of named species have been assessed in terms of their conservation status. Of those that have, birds have the lowest percentage of threatened species, at 12%. The patterns of threat are broadly similar for mammals and conifers, which have 23% and 25% of species threatened, respectively. The situation with amphibians looks similar, with 32% threatened, but information is more limited, so this may be an underesti- mate. Cycads have a much higher proportion of threatened species, with 52% globally threatened. In regional assessments, taxonomic groups with the highest proportion of threatened species tended to be those that rely on freshwater habitats (). Threatened species show continuing declines in conservation status, and species threat rates tend to be highest in the realms with highest species richness (). (See Figures and ) Threatened vertebrates are most numerous in the biomes with intermediate levels of habitat conversion. Low-diversity biomes (such as boreal forest and tundra) have low species richness and Source; Butchart et al. 2005 44 Ecosystems and Human Well-being: Biodiversity Synthesis
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