Amphibians are a unique group of animals that live on every continent except for Antarctica. Loads of amphibian species are threatened, and many are listed as endangered by the International Union for Conservation of Nature (IUCN). Many amphibians are incredibly fragile, partly due to their unique way of breathing. Minute changes in their environment can lead to a species becoming endangered, or worse. The rate of extinction of amphibians is higher than almost every other group of organisms. So, why are some endangered amphibians going extinct?
There are a few main reasons why some amphibian species are disappearing. Before we get into them, we need to first understand global amphibian diversity, and why the decline of these animals is alarming.
Worldwide, there are over 7,000 species of amphibians. These include frogs, salamanders, and snake-like creatures called caecilians. The place with the highest amphibian diversity is the Amazon rainforest. Nearly a third of all amphibian species are at least threatened, and hundreds are listed as critically endangered.
Amphibians are often good indicator species. When frog or salamander populations start to decline, it can be a sign that there are small changes in the environment. This can range from a change in temperature to the introduction of a pollutant in a stream or pond. In any case, a changing amphibian community often tips us off that something is beginning to change in the environment. Sometimes, we can then identify an environmental problem before it gets too bad. The fact that amphibian populations decline in part due to climate change could be a bad omen for many other organisms.
The decline of amphibians worldwide is alarming. What exactly is causing frogs, salamanders, and caecilians to struggle to survive? Like with many endangered species, there’s more than just one reason.
One of the main threats to many plants and animals is habitat destruction. Amphibians are no exception. In the US alone, less than 0.01% of native grasslands remain. Wetlands, ponds, and forests are more habitat types important for amphibians that humans are disturbing more and more. Unfortunately, many amphibians have very small home ranges and are unable to move from habitat to habitat, which makes habitat fragmentation also very impactful to amphibians.
Amphibians are incredibly sensitive to small changes in their environment. This is partly what makes them such great indicator species. However, it’s also what makes them extremely susceptible to climate change and changing temperatures. One major impact climate change has on frogs is that it changes when they breed. Many species are breeding earlier in the year due to warmer temperatures. When this happens, it’s possible there is not enough food for their young once the tadpoles hatch, and many are unable to make it to adulthood. A more indirect impact may include climate change affecting amphibian immune systems, which makes them more prone to disease.
Perhaps the most terrifying reason some amphibians are going extinct is a fungal disease called chytridiomycosis. The disease is caused by the fungus Batrachochytrium dendrobatidis, commonly called the chytrid fungus. The origin of the fungus is likely Asia, but it’s now spread throughout much of the world. Unfortunately, the disease is spreading fast and affecting amphibians all over the world. It’s said to be the single greatest disease-caused loss of biodiversity in recorded history.
One of the poster children for animal extinctions and amphibian conservation is the golden toad. A small, brilliantly colored toad once lived in a tiny area in Monteverde, Costa Rica. In fact, it’s native range was only 4 square kilometers (1.5 square miles). Despite its small home range, the golden toad was abundant. There were estimated to be around 1500 individuals from their discovery in 1964 until 1987. Then, in 1988, researchers only saw 10 individuals. The next year, none. Since 1989, not a single golden toad has been spotted. In just three years, an entire species went from being happy and healthy to extinct entirely.
How did this happen? There are different schools of thought. Some think a dryer than normal year in 1987 led to the disappearance of the golden toad. Others believe it was airborne pollution. Another supported theory blames chytrid fungus. Although there’s no possibility of ever knowing the answer, the most likely cause was all three together. A combination of climate change, pollution, and chytrid fungus was a perfect storm to cause the golden toad to go extinct.