Decline in amphibian populations in the context of "Batrachochytrium dendrobatidis"

There are several plausible pathways that could lead to plant and animal species extinction from climate change. Every species has evolved to exist within a certain ecological niche, but climate change leads to changes of temperature and average weather patterns. These changes can push climatic conditions outside of the species' niche, and ultimately render it extinct. Normally, species faced with changing conditions can either adapt in place through microevolution or move to another habitat with suitable conditions. However, the speed of recent climate change is very fast. Due to this rapid change, for example cold-blooded animals (a category which includes amphibians, reptiles and all invertebrates) may struggle to find a suitable habitat within 50 km of their current location at the end of this century (for a mid-range scenario of future global warming).

Climate change also increases both the frequency and intensity of extreme weather events, which can directly wipe out regional populations of species. Those species occupying coastal and low-lying island habitats can also become extinct by sea level rise. This has already happened with Bramble Cay melomys in Australia. Finally, climate change has been linked with the increased prevalence and global spread of certain diseases affecting wildlife. This includes Batrachochytrium dendrobatidis, a fungus that is one of the main drivers of the worldwide decline in amphibian populations.

Amphibians are ectothermic, anamniotic, four-limbed vertebrate animals that constitute the class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all tetrapods, but excluding the amniotes (tetrapods with an amniotic membrane, such as modern reptiles, birds and mammals). All extant (living) amphibians belong to the monophyletic subclass Lissamphibia, with three living orders: Anura (frogs and toads), Urodela (salamanders), and Gymnophiona (caecilians). Evolved to be mostly semiaquatic, amphibians have adapted to inhabit a wide variety of habitats, with most species living in freshwater, wetland or terrestrial ecosystems (such as riparian woodland, fossorial and even arboreal habitats). Their life cycle typically starts out as aquatic larvae with gills known as tadpoles, but some species have developed behavioural adaptations to bypass this.

Young amphibians generally undergo metamorphosis from an aquatic larval form with gills to an air-breathing adult form with lungs. Amphibians use their skin as a secondary respiratory interface, and some small terrestrial salamanders and frogs even lack lungs and rely entirely on their skin. They are superficially similar to reptiles like lizards, but unlike reptiles and other amniotes, require access to water bodies to breed. With their complex reproductive needs and permeable skins, amphibians are often ecological indicators to habitat conditions; in recent decades there has been a dramatic decline in amphibian populations for many species around the globe.

Chytridiomycosis (/kaɪˌtrɪdiəmaɪˈkoʊsɪs/ ky-TRID-ee-ə-my-KOH-sis) is an infectious disease in amphibians, caused by the chytrid fungi Batrachochytrium dendrobatidis and Batrachochytrium salamandrivorans. Chytridiomycosis has been linked to dramatic population declines or extinctions of amphibian species in western North America, Central America, South America, eastern Australia, east Africa (Tanzania), and Dominica and Montserrat in the Caribbean. Much of the New World is also at risk of the disease arriving within the coming years. The fungus is capable of causing sporadic deaths in some amphibian populations and 100% mortality in others. No effective measure is known for control of the disease in wild populations. Various clinical signs are seen by individuals affected by the disease. A number of options are possible for controlling this disease-causing fungus, though none has proved to be feasible on a large scale. The disease has been proposed as a contributing factor to a global decline in amphibian populations that apparently has affected about 30% of the amphibian species of the world. Some research found evidence insufficient for linking chytrid fungi and chytridiomycosis to global amphibian declines, but more recent research establishes a connection and attributes the spread of the disease to its transmission through international trade routes into native ecosystems.

The golden toad (Incilius periglenes) is an extinct species of true toad that was once abundant in a small, high-altitude region of about 4 square kilometres (1.5 mi) in an area north of the city of Monteverde, Costa Rica. It was endemic to elfin cloud forest. Also called the Monte Verde toad, Alajuela toad and orange toad, it is commonly considered the "poster child" for the amphibian decline crisis. This toad was first described in 1966 by herpetologist Jay Savage. The last sighting of a single male golden toad was on 15 May 1989, and it has since been classified as extinct by the International Union for Conservation of Nature (IUCN). The golden toad was declared extinct by the IUCN Red List in 2005.