Amphibians lead a double life – and have it particularly tough
The fact that amphibians or salamanders live both in water and on land makes them particularly sensitive to changing environmental conditions. As larvae, when they still breathe through their gills, amphibians are highly susceptible to water pollution. In their later adult stage, whether as frogs, toads, salamanders, or newts, they rely on clean water for breeding but still require an intact habitat outside the water.
Thus, the main reason for the decline in amphibian populations is the destruction of their habitats due to pollution or drying up of water bodies, soil sealing, and landscape fragmentation due to urbanization. Additionally, pesticides used in agriculture have negative effects.
Invasive species, such as cats or rats, also displace amphibians – especially when they have a very small range, which is very common. For example, the golden toad, which became extinct in 1989, was found in only a four-square-kilometer area in Costa Rica’s cloud forest.
If the range is small and the amphibian is rare, collecting the animals can quickly lead to the extinction of a species. This happened with the poisonous splendid poison frog; its striking red coloration made it extremely popular in the international exotic and pet trade. It disappeared in 1992.
Many amphibians that became extinct in the 19th century suffered from the destruction of their habitat. The Günther’s dwarf frog, measuring less than three centimeters, was discovered and scientifically described in 1882 in Sri Lanka and then never seen again. It is believed that the deforestation of much of Sri Lanka’s forests led to its disappearance. The same applies to the Sri Lankan leopard bubble nest frog, which has not been sighted since 1859, and the Maia bubble nest frog, which is only known from two specimens collected in 1876.
Extinct amphibians due to chytridiomycosis?
Especially in the last 25 years, the fungal disease chytridiomycosis, which is often discussed in connection with the global decline of amphibians, has played a significant role in the population decline of amphibian species. Researchers today agree that chytridiomycosis cannot be considered the sole cause of amphibian decline.
There are many factors that can predispose amphibians to infection with the fungal disease. These include suboptimal climate and environmental conditions, inappropriate nutrition, stress, and climatic changes. Nevertheless, it is undeniable that infection with this disease ultimately leads to the drastic decline or even extinction of populations of many amphibian species. Examples include the Chiriqui harlequin frog, the Corquin robber frog, and Rabb’s fringe-limbed treefrog – chytridiomycosis played a role in the extinction of all of these, even though other factors certainly contributed to the fungal disease.
Extinct amphibians: Data & facts (as of 10/2023)
Out of over 8,000 amphibian species, the International Union for Conservation of Nature (IUCN) lists 36 species as extinct on their Red List. The actual number is much higher, as many species have not been listed yet or have been considered missing for decades. Among the 722 “critically endangered” amphibian species, according to the IUCN, 156 species are “likely extinct”.
Out of the 36 officially extinct species, 18 come solely from Sri Lanka (e.g., the tree frog Pseudophilautus temporalis or the Sri Lanka bubble-nest frog). In Central America, including Honduras, Guatemala, Panama, and Costa Rica, nine species have disappeared, such as McCranie’s robber frog. In Queensland, Australia, four frog species have gone extinct (e.g., the southern gastric-brooding frog).
However, it’s not just frogs that have disappeared; salamanders or newts are also affected, such as Ainsworth’s salamander, last seen in 1964, the Jalpa false brook salamander, which disappeared in 1976, or the Wolterstorff’s newt from China, not seen since 1979.
The Blanco blind salamander, last seen in 1951 and native to Texas (USA), is not listed by the IUCN. It is considered missing; there is neither evidence of its existence nor its extinction. The species lacks or has only rudimentary eyes and is endemic to underground, groundwater-filled caves.