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Weird Science: Amphibians in Decline

SF Fig. 5.1. The golden toad (Bufo periglenes) of Costa Rica is now extinct in the wild.

Image courtesy of U.S. Fish and Wildlife Service (USFWS)

Populations of amphibians are in rapid decline around the world. This phenomenon was first observed in Europe in the 1950s. By the 1990s, scientists had reported more than 500 amphibian species on five continents with plummeting populations. In 2004, an international team of over 500 scientists noted that 32 percent of all amphibian species are considered “threatened with extinction” and 43 percent are decreasing in population. Many scientists consider this to be a mass extinction event since amphibians are going extinct 211 times faster than the expected or background extinction rate. Unlike previous extinction events in Earth’s history, the current mass extinction of amphibians is likely caused by human activity.


Many explanations for the global amphibian decline have been proposed. The destruction, degradation, and fragmentation of habitat has had an immediate impact on amphibians. Water pollution can also negatively affect amphibians since all amphibian species rely on water at some point in their life cycle. Non-native invasive species, particularly freshwater fish, can great reduce amphibian populations by preying on submerged egg masses and frog tadpoles. Global climate change and atmospheric ozone loss threaten amphibians since many species are highly sensitive to drought, extreme temperatures, and ultraviolet radiation. These factors have also been linked to an increase in amphibian diseases. A fungal disease called chytridiomycosis has caused mass mortality events in frogs and salamanders in Australia, North America, and South America. Scientists have strong evidence that increases in air temperature and cloud cover due to global climate change have aided the spread of the chytrid fungus. Climate change and water pollution have also been linked to increases in parasitic flatworm infections in amphibians. These flatworm infections can cause missing, malformed, or extra limbs in amphibians and significantly reduce their likelihood of survival (SF Fig. 5.2).

SF Fig. 5.2. (A) Pacific tree frog (Pseudacris regilla) with additional hind limbs caused by a parasitic flatworm infection

Image courtesy of Brett A. Goodman and Pieter T.J. Johnson, University of Colorado Boulder

SF Fig. 5.2. (B) Spotted salamander (Ambystoma maculatum) with five feet at University of Mississippi Field Station

Image courtesy of Matthew Pintar, Wikimedia Commons

Scientists around the world continue their research to improve our understanding of the causes of amphibian declines and extinctions. They work with government and community groups to conserve these important species by reducing water pollution, protecting crucial amphibian habitat, and captive breeding endangered species.

Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.