Amphibians as indicators

“Reptiles and amphibians are sometimes thought of as primitive, dull and dim witted. In fact, of course, they can be lethally fast, spectacularly beautiful, surprisingly affectionate and very sophisticated” - David Attenborough. Amphibians have survived on earth for 300 million years longer than humanity and have gone through some unusual evolutionary changes over their period of settlement. Over 8000 known species of amphibians exist and they comprise frogs, toads, salamanders, newts and caecilians. Although morphologically similar to the class of reptiles, amphibians have adaptations which allow them to survive in land and water. In order to survive, amphibians are dependent on pristine freshwater habitats as they are vulnerable to habitat degradation.

An ecological indicator is an organism which provides relevant data about an ecosystem and the impacts of human activity on it. Amphibians are considered ecological indicators as they have complex reproductive requirements and porous skins. Therefore, slight changes in ecosystems can negatively impact amphibian populations and in recent decades, there has been a dramatic decline in the populations of amphibian species around the world. Approximately 32% of amphibians are threatened with extinction and this decline is majorly attributed to human activity.

Amphibian populations are undergoing a serious decline in various regions of the world. Unfortunately, the causes for amphibian population declines have been difficult to assess. Causes for the declines include habitat destruction (the most obvious cause), climate change, pathogens, introduced exotic species, pollution, and increased UV radiation. Like many other organisms, increasing ultraviolet-B radiation due to stratospheric ozone depletion and other factors may harm the DNA of amphibians, particularly their eggs. 

Habitat modification or destruction is one of the most dramatic issues affecting amphibian species worldwide. As amphibians generally need aquatic and terrestrial habitats to survive, threats to either habitat can affect populations. Hence, amphibians may be more vulnerable to habitat modification than organisms that only require one habitat type. Large scale climate changes may further be modifying aquatic habitats, preventing amphibians from spawning altogether. Habitat fragmentation occurs when habitats are isolated by habitat modification, such as when a small area of forest is completely surrounded by agricultural fields. Small populations that survive within such fragments are often susceptible to inbreeding, genetic drift, or extinction due to small fluctuations in the environment.

A number of diseases have been related to mass die-offs or declines in populations of amphibians. It is not entirely clear why these diseases have suddenly begun to affect amphibian populations, but some evidence suggests that these diseases may have been spread by humans, or may be more virulent when combined with other environmental factors