All known amphibian species have been assessed using the IUCN Red List categories and criteria. These categories provide an explicit framework for determining a species' conservation status, with an emphasis on identifying those at highest risk of global extinction. In this context, the term "Threatened" refers to those species classified under IUCN Red List categories of Vulnerable, Endangered, or Critically Endangered.
Of the 6,260 amphibian species assessed, nearly one-third of species (32.4 %) are globally threatened or extinct, representing 2,030 species (Figure 1). Thirty-eight of the 2,030 species are considered to be Extinct (EX), and one Extinct in the Wild (EW). Another 2,697 species are not considered to be threatened at present, being classified in the IUCN Categories of Near Threatened (NT) or Least Concern (LC), while sufficient information was not available to assess the status of an additional 1,533 species (IUCN Category Data Deficient (DD)). It is predicted that a significant proportion of these Data Deficient species are likely to be globally threatened.
|Legend Key||Red List Category||Number of species||Percentage in category|
|Extinct in the Wild (EW)||1||0.02|
|Critically Endangered (CR)||489||7.8|
|Near Threatened (NT)||381||6.1|
|Least Concern (LC)||2,316||37.0|
|Data Deficient (DD)||1,533||24.5|
Documenting population trends is a key to assessing species status, and a special effort was made to determine which species are declining, stable, or increasing. The assessment found declines to be widespread among amphibians, with 42.5 % of species reported to be in decline. In contrast, 26.6 % appear to be stable and just 0.5 % are increasing. Because trends information is not available for 30.4 % of species, however, the percentage of species in decline may actually be considerably higher.
Extinctions are often difficult to confirm. Using the most conservative approach to documenting extinctions, just 38 amphibians are known to have become extinct since the year 1500. Of greater concern, however, are the many amphibians that are missing and can no longer be found. Until exhaustive surveys probing their disappearance can be carried out, these species cannot be classified in the IUCN Red List category of Extinct, but rather are flagged as "possibly extinct" within the Critically Endangered category. The assessment documents 120 such possibly extinct species.
Unfortunately, there is strong evidence that the pace of extinctions is increasing. Of the 38 known extinctions, 9 have occurred since 1980, including such species as the golden toad (Bufo periglenes) of Monteverde, Costa Rica. Among those amphibians regarded as "possibly extinct", most have disappeared and not been seen since 1980. Fortunately, a few amphibians that previously were thought to be extinct have been rediscovered. For example, Atelopus cruciger was not seen in its native Venezuela after 1986, until a tiny population was found in 2003.
Amphibians comprise three major groups, or taxonomic orders: Anura (frogs and toads), Caudata (salamanders and newts), and Gymnophiona (caecilians). Significant differences exist among these groups in both species numbers as well as threatened status. For instance, there is an order of magnitude more frogs and toads than salamanders and newts, and even fewer caecilians are known. Frogs and toads, with 5,532 species very much drive the average threat level for amphibians as a whole with 31.6% (1,749 species) either threatened or extinct. However, salamanders and newts show significantly higher threat levels, with 49.8% (275 species) of their species threatened or extinct. Caecilians, in contrast, appear to be relatively secure with just 3.4 % (6 species) threatened. However, two-thirds (67 % ) of caecilians are so poorly known that they have been assessed as Data Deficient.
Frogs & Toads
Salamanders & Newts
Significant difference in threat levels is also exhibited at the level of taxonomic Family, as show in Table 3. Since the assessment was first completed in 2004 there has been a major revision of amphibian families following the taxonomic changes proposed by Frost et al. 2006, and these taxonomic changes were adopted in the 2008 update. In the table below the threat levels are shown in the new arrangement of families.
Diverse families of frogs and toads (more than 100 species) that are more threatened than the global average include the Bufonidae, Craugastoridae, Eleutherodactylidae, Rhacophoridae, and Strabomantidae. Very diverse families (more than 200 species) that are less threatened than the global average include Microhylidae, Hyperoliidae, Hylidae and Ranidae. Among larger salamander families, Hynobiidae and Plethodontidae exhibit much higher levels of threat than Salamandridae.
All four species of the newly established family Calyptocephalellidae are threatened. All four species are endemic to Chile and are highly aquatic larval developers. The only other family with all species threatened is Sooglossidae, which was previously considered endemic to the Seychelles. Under the new taxonomic arrangement the family Nasikabatrachidae with its one species found in the Western Ghats of southern India is also now included in the Sooglossidae. The previously recognized Australian endemic family Rheobatrachidae (the gastric-brooding frogs), with only two species and both now Extinct, is now included in the family Myobatrachidae under the new taxonomic arrangement. Also under the new arrangement the family Leiopelmatidae, previously endemic to New Zealand, now includes two species previously in the no longer recognized family Ascaphidae. The four original species of Leiopelmatidae, the only amphibians native to New Zealand, are all still considered threatened.
Nasikabatrachus sahyadrensis (a frog), India. Photo © S.D. Biju.
Chinese Giant Salamander (Andrias davidianus), China. Photo © Michael Lau - Kadoorie Farm and Botanic Garden.
|FAMILY||TOTAL||EX||EW||CR||EN||VU||NT||LC||DD||% Threatened or Extinct|
The number of species in each IUCN Red List category in each of the hundreds of amphibian genera can be accessed here
Frost, D.R., Grant, T., Faivovich, J., Bain, R.H., Haas, A., Haddad, C.F.B., De Sá, R.O., Channing, A., Wilkinson, M., Donnellan, S.C., Raxworthy, C.J., Campbell, J.A., Blotto, B.L., Moler, P., Drewes, R.C., Nussbaum, R.A., Lynch, J.D., Green, D.M. and Wheeler, W.C. 2008 The Amphibian Tree of Life. Bulletin of the American Museum of Natural History, 297.