Species Diversity Within and Among Ecosystems - Ecological Systems - page 258

Extinct (EX)

Extinct in the wild (EW)

Threatened categories

Critically endangered (CR)

Extinction
risk

Adequate data

Endangered (EN)

Vulnerable (VU)

Evaluated

Near threatened (NT)

Least concern (LC)

All species

Data deficient (DD)

Not evaluated (NE)

Fig. 14.1 The IUCN red list of threatened species provides taxonomic, conservation status, and

distribution information on species that have been globally evaluated using the IUCN red list
categories and criteria

™

of the world's overall species [ 39 ]. Recent efforts to assess whether vertebrates
trends and patterns can be used to extrapolate for other taxonomic groups are
ongoing and show promise, with initial assessments indicating that the threat levels
seen in invertebrate groups are not dissimilar from that of vertebrates [ 40 ].
The IUCN Red List of Threatened Species is the most widely accepted standard
for assessing species' risk of extinction [ 41 ]. The IUCN Red List assesses species
according to five quantitative criteria and classifies them into one of eight categories
(see Fig. 14.1 ). Regular assessments of taxonomic groups provide information on
trends in extinction risk, known as the IUCN Red List Index (RLI). The RLI
considers species classified as Critically Endangered, Endangered, or Vulnerable
to be threatened with extinction and explicitly accounts for Data Deficient species.
Comprehensive datasets exist for mammals [ 42 ], birds [ 43 , 44 ], and amphibians
[ 45 ], while sampled assessments can be used for other taxa [ 38 ]( Fig. 14.2 ).
Trends in vertebrate populations have been measured using the Living Planet
Index, a global biodiversity indicator that tracks changes in vertebrate populations
in the wild. It contains data on species trends from 1970 to 2005 and is calculated by
aggregating population time series for each taxonomic group where data is avail-
able [ 46 ]. However, results for individual classes are at this point considered
preliminary and conservative due to limited data or data biased toward temperate
regions [ 38 ].

Mammals

Mammals are found across the world's terrestrial and aquatic ecosystems, with
South American, sub-Saharan Africa, and Southeast Asia containing the highest
concentrations of species of terrestrial mammals. The highest species richness of