Human Civilization - A Threat to Global Amphibian Diversity

Dramatic declines in amphibian populations, including population crashes and mass localised extinctions, have been noted since the 1980s from locations all over the world. These declines are perceived as one of the most critical threats to global biodiversity, and several causes are believed to be involved, including disease, habitat destruction and modification, exploitation, pollution, pesticide use, introduced species, climate change and increased ultraviolet-B radiation (UV-B). However, many of the causes of amphibian declines are still poorly understood, and the topic is currently a subject of much ongoing research.

Because amphibians generally have a two-staged life cycle consisting of both aquatic (larvae) and terrestrial (adult) phases, they are sensitive to both terrestrial and aquatic environmental effects. Because their skins are highly permeable, they may be more susceptible to toxins in the environment than other organisms, such as, birds or mammals. Habitat modification or destruction is one of the most dramatic issues affecting amphibian species world wide. 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.

There is evidence of chemical pollutants causing frog developmental deformities (extra limbs, or malformed eyes). Pollutants have varying effects on frogs. Some alter the central nervous system; others like atrazine cause a disruption in the production and secretion of hormones. Like many other organisms, increasing Ultraviolet-B (UV-B) radiation due to stratospheric ozone depletion and other factors may harm the DNA of amphibians, particularly their eggs. The amount of damage depends upon the life stage, the species type and other environmental parameters. Another possible cause of global declines is the collection of frogs as a food source.

Frogs being covered by a semi permeable skin are vulnerable to pollutnts and other environmentl stress. Consequently they can be used as environmental sentinels or biomonitors and can act as an early warning system for the quality of the environment and the potential threats to other animals including ourselves.