Why Are Amphibians in Decline?

The Factors Behind the Devastation of Amphibian Populations

Red-eyed tree frog.
Red-eyed tree frog. Photo © Alvaro Pantoja / ShutterStock.

In recent years, scientists and conservationists have been working to raise public awareness of a global decline in amphibian populations. Herpetologists first started noting that amphibian populations were falling at many of their study sites in the 1980's; however, those early reports were anecdotal, and many experts doubted that the observed declines were cause for concern (the argument was that populations of amphibians fluctuate over time and the declines could be attributed to natural variation).

See also 10 Recently Extinct Amphibians

But by 1990, a significant global trend had emerged—one that clearly overstepped normal population fluctuations. Herpetologists and conservationists started voicing their concern about the worldwide fate of frogs, toads and salamanders, and their message was alarming: of the estimated 6,000 or so known species of amphibians that inhabit our planet, nearly 2,000 were listed as endangered, threatened or vulnerable on the IUCN Red List (Global Amphibian Assessment 2007).

Amphibians are indicator animals for environmental health: these vertebrates have delicate skin that readily absorbs toxins from their environment; they have few defenses (aside from poison) and can easily fall prey to non-native predators; and they rely on the proximity of aquatic and terrestrial habitats at various times during their life cycles. The logical conclusion is that if amphibians populations are in decline, it is likely that habitats in which they live are also degrading.

There are numerous known factors that contribute to amphibian declines—habitat destruction, pollution, and newly introduced or invasive species, to name just three. Yet research has revealed that even in pristine habitats—those that lie beyond the reach of bulldozers and crop-dusters—amphibians are disappearing at shocking rates.

Scientists are now looking to global, rather than local, phenomena for an explanation of this trend. Climate change, emerging diseases, and increased exposure to ultraviolet radiation (due to ozone depletion) are all additional factors that could be contributing to falling amphibian populations.

So the question 'Why are amphibians in decline?' has no simple answer. Instead, amphibians are disappearing thanks to a complex mixture of factors, including:

  • Alien Species. Native amphibian populations can suffer decline when alien species are introduced into their habitats. An amphibian species may become the prey of the introduced species; alternatively, the introduced species may compete for the same resources required by the native amphibian. It is also possible for introduced species to form hybrids with native species, and so reduce the prevalence of the native amphibian within the resulting gene pool.
  • Over-Exploitation. Amphibian populations in some parts of the world are declining because frogs, toads and salamanders are captured for the pet trade or are harvested for human consumption.
  • Habitat Alteration and Destruction. Alteration and destruction of habitat has devastating effects on many organisms, and amphibians are no exception. Changes to water drainage, vegetation structure, and habitat composition all impact the ability of amphibians to survive and reproduce. For example, the drainage of wetlands for agricultural use directly reduces the range of habitat available for amphibian breeding and foraging.
  • Global Changes (Climate, UV-B, and Atmospheric Changes). Global climate change presents a serious threat to amphibians, because altered precipitation patterns usually result in changes to wetland habitats. Additionally, increases in UV-B radiation due to ozone depletion have been found to severely impact some amphibian species.
  • Infectious Diseases. Significant amphibian declines have been associated with infectious agents such as the chytrid fungus and iridoviruses. A chytrid fungal infection known as chytridiomycosis was first discovered in populations of amphibians in Australia, but also has been found in Central America and North America.
  • Pesticides and Toxins. The widespread use of pesticides, herbicides, and other synthetic chemicals and pollutants has severely impacted amphibian populations. In 2006, scientists at the University of California, Berkeley found that mixtures of pesticides were causing amphibian deformities, reducing reproductive success, harming development of juveniles, and increasing amphibians' susceptibility to diseases such as bacterial meningitis.

    Edited on February 8, 2017 by Bob Strauss

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    Strauss, Bob. "Why Are Amphibians in Decline?" ThoughtCo, Oct. 12, 2017, thoughtco.com/why-amphibians-are-in-decline-129435. Strauss, Bob. (2017, October 12). Why Are Amphibians in Decline? Retrieved from https://www.thoughtco.com/why-amphibians-are-in-decline-129435 Strauss, Bob. "Why Are Amphibians in Decline?" ThoughtCo. https://www.thoughtco.com/why-amphibians-are-in-decline-129435 (accessed December 12, 2017).