Amphibian Declines on FrogWeb

FrogWeb: Amphibian Declines

Class Amphibia - frogs and toads, newts and salamanders, and caecilians - first appeared on Earth during the Devonian Period (360 to 408 million years ago). While many amphibian species have evolved and gone extinct over the millenia, more than 5000 species exist today. Various amphibians have adapted over this expanse of time to occupy different habitats, including wetlands, forests, deserts, prairies, and savannas. By the time human civilizations were established, amphibians were present in all but the most inhospitable of regions. Until recently, whether you lived in a city, a suburb, or a rural area anywhere in the world, chances are you weren't too far away from a frog, toad, salamander, or caecilian.

So what has changed? In short, the number of amphibians out there.

Amphibian populations are in decline in many areas of the world. In cities and the countryside, in rainforests and wetlands, countless areas which previously hosted a range of healthy amphibian populations now have fewer - and even no - frogs, toads, and salamanders. While healthy populations of some species may exist elsewhere in some cases of declines, a few species - including Costa Rica's Monteverde golden toad and Australia's Gastric brooding frog - are now believed extinct.

What's causing these mysterious declines? Scientists conducting field research have produced compelling evidence for habitat loss, climate change, UV radiation, contaminants and pollutants, disease, and predation by invasive species as possible causes. Even more baffling, amphibian declines are not necessarily occurring in "likely" places where human impacts are obvious, such as cities and suburbs prone to development and pollution; indeed, some of the most noted and dramatic declines are happening in "protected" areas such as national parks.

The scientific community now suspects that there is no one reason for worldwide declines of amphibians. For example, diseases or pollutants that have decimated a species in one part of the world may be completely absent in another region that has also experienced a mysterious die-off of its amphibians. In some cases, die-offs can be attributed to a specific cause; in others, the cause is not so obvious. Many researchers believe that multiple, additive causes - for instance, a high incidence of UV radiation combined with the presence of a disease - may be at the heart of large numbers of worldwide declines.

As research continues into amphibian declines phenomena, FrogWeb will make available the latest findings, which can be accessed from the menus below.