Why is the amphibian population declining?

The decline in amphibian populations is an ongoing mass extinction of amphibian species worldwide. Since the 1980s, mass localized extinctions and huge decreases in populations have been observed in many locations throughout the world(1).

These declines are known as one of the most critical threats to global biodiversity. But why is the amphibian population declining? From habitat modification and fragmentation to introduced predators or other species, pollution, pesticides, or over-harvesting, these are among the key factors for the amphibian decline.

About amphibians

Amphibians are small vertebrates that need water, or a moist environment, to survive. The species in this group include frogs, toads, salamanders, and newts. All can breathe and absorb water through their skin, which is very thin(2).

They have special skin glands that produce useful proteins. Some transport water, oxygen, and carbon dioxide either into or out of the animal. Others fight bacteria or fungal infections, and at least one in each species is used for defense.

This group of vertebrates contains over 7,000 known species, and many of them are threatened worldwide. A 2004 global assessment found that around 32% of the world’s amphibians are threatened, representing 1,856 species.

Many reasons amphibians are vulnerable

Amphibians have been around for over 300 million years, however, in just the last two decades there has been an alarming number of extinctions.

Nearly 168 species are theorized to have gone extinct and at least 2,469 more have declining populations.

Why are populations declining?

Many factors contribute to the amphibian decline. Habitat destruction, pollution, and newly introduced or invasive species, to name a few. The most important factor is habitat destruction(3).

Since so many forests are cleared, it is no surprise that species that once lived there disappear. However, there are instances where the habitat is protected, but the amphibians are still disappearing.

There are many reasons for this however, an emerging disease called chytridiomycosis and global climate change are thought to be the biggest threats to amphibians.

Chytridiomycosis is a disease caused by the fungal chytrid pathogen Batrachochytrium dendrobatidis. This pathogen is associated with the global loss of hundreds of species of amphibians and represents a great loss of biodiversity, many believe it to be the worst in recorded history(4).

Amphibians are disappearing due to a complex mixture of factors such as:

* Alien species – introduced into their habitats; since they compete with the native amphibians for the same resources.

* Over-exploitation – frogs, toads, and salamanders are captured for the pet trade or are harvested for human consumption.

* Habitat alteration and destruction – these actions have devastating effects on many organisms, reducing their habitat.

* Global changes – such as climate, UV-B, and atmospheric changes. They represent a serious threat to amphibians since altered precipitation patterns usually result in changes to wetland habitats.

* Infectious diseases – the chytrid fungus and iridoviruses have played a significant role in the declines of the amphibians.

* Pesticides and toxins – pesticides, herbicides, and other synthetic chemicals and pollutants have severely impacted amphibian populations.

Did you know?

– In 2006, scientists at the University of California, Berkeley found that mixtures of pesticides were causing amphibian deformities, reproductivity issues, harming the development of juveniles, and overall increasing the amphibian’s susceptibility to diseases such as bacterial meningitis.

– The Golden toad of Monteverde, Costa Rica, was among the first casualties of amphibian declines. It was last seen in 1989.

– Certain studies concluded that the amphibian populations in the US were shrinking at a rate of 3.7% each year. This means that the species could disappear in the next 20 years. (The studies were conducted in 2013.)