Amphibians and habitat destruction
Amphibians are a class of vertebrate animals characterized by their thin, permeable skin, which allows them to breathe primarily through their skin. This unique biological feature, combined with their life cycle that includes both aquatic larvae and terrestrial adults, makes them particularly sensitive to habitat alterations and environmental contaminants. Unfortunately, amphibian populations worldwide are experiencing significant declines, with 41 percent of species threatened with extinction as of 2023, primarily due to habitat destruction, pollution, and the spread of diseases like chytridiomycosis, caused by a harmful fungus. The destruction of habitats, especially in tropical regions, and the impact of climate change exacerbate these issues.
Amphibians also play a crucial role in their ecosystems, serving as indicators of environmental health. Their decline can signal broader ecological problems that may eventually affect other species, including humans. In addition to natural threats, human activities have led to the introduction of invasive amphibian species, which can disrupt local ecosystems by preying on or competing with native species. These complex interactions highlight the vulnerability of amphibians and underscore the need for conservation efforts to safeguard their habitats and populations.
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Amphibians and habitat destruction
DEFINITION: Class of vertebrate animals with thin, permeable skin and generally characterized by an aquatic larval stage and a more or less terrestrial adult stage
Amphibian populations have been suffering worldwide declines as a consequence of habitat destruction and alteration, parasites and diseases, and pollution, to which their permeable skin renders them particularly vulnerable.
Amphibians include frogs and toads, salamanders, and caecilians (rarely encountered legless tropical forms). Because nearly all amphibians lead double lives, they are affected by alterations and environmental contaminants in both aquatic environments (as larvae, such as tadpoles) and terrestrial environments (as adults). Also, because amphibians breathe primarily through their skin, they are very sensitive to chemicals and to poor water quality. Like the proverbial canary in the mine, amphibians serve as environmental monitors. Consequently, declining amphibian populations are of concern not only because amphibians are important components of many ecosystems but also because the declines may signal the onset of deteriorating conditions that will soon affect other forms of life, including humans.
According to the International Union for Conservation of Nature, 41 percent of the world’s amphibian species were threatened with extinction as of 2023. Most of the declines are attributable to habitat alterations and destruction. Especially in the Tropics, deforestation has affected a number of species, and the cool, wet mountaintop habitats favored by many amphibians are particularly vulnerable to global climate change. Complicating the issue is the rapid worldwide spread of the chytrid fungus, which has devastated amphibian populations. The fungus invades the thin skin of amphibians and kills them by disrupting their ability to regulate the movement of water and oxygen in their bodies. The fungus spreads in water and through direct body contact. A few resistant species, such as bullfrogs, clawed frogs, and cane toads, serve as vectors, transmitting the disease to sensitive species. Chytrid thrives in the same cool, wet conditions favored by most amphibians.
Deformed frogs with missing or extra limbs were brought to the attention of the world when they were discovered by schoolchildren in Minnesota in 1995. At first, chemical pollutants were thought to be the cause, but it became apparent that parasitic flatworms (trematodes) were responsible. However, experts believe that, like chytrid, stress imposed by deteriorating habitats and a changing climate may well be aggravating the problem in a synergistic fashion.
Another environmental concern associated with amphibians is not related to declines but is, in fact, caused by too many frogs in the wrong places. A few very hardy species have been transported by humans to places far from their native ranges. These invasive species upset biotic communities by competing with or eating native species. Large and voracious cane toads, introduced widely to control insect pests in sugarcane fields, have been implicated in the decline or extinction of native frogs in places as far from one another as Florida and Australia. Equally large and voracious bullfrogs, intentionally imported around the world for food, are responsible for declines of native frogs in the western United States, Latin America, and even Europe. Coquís, small tree frogs native to Puerto Rico, pose a threat to unique Hawaiian insects. Cuban tree frogs, introduced into Florida, have hitchhiked on tropical plants shipped around the world, and in their new habitats they eat other frogs and even small lizards.
Bibliography
Collins, James P., and Martha L. Crump. Extinction in Our Times: Global Amphibian Decline. New York: Oxford University Press, 2009.
Heatwole, Harold, and John W. Wilkinson, eds. Amphibian Decline: Diseases, Parasites, Maladies, and Pollution. Chipping Norton, N.S.W.: Surrey Beatty & Sons, 2009.
"IUCN SSC Amphibian Specialist Group." International Union for Conservation of Nature, 2024, www.iucn.org/our-union/commissions/group/iucn-ssc-amphibian-specialist-group. Accessed 12 July 2024.
Lannoo, Michael, ed. Amphibian Declines: The Conservation Status of United States Species. Berkeley: University of California Press, 2005.
Stuart, S. N., et al., eds. Threatened Amphibians of the World. Arlington, Va.: Conservation International, 2008.