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Although scientists observed reduction in populations of several European amphibian species since the 1950s, awareness of the decline of amphibian populations and its classification as a modern-day global mass extinctions world only dates from the 1980s. By 1993, more than 500 species of frogs and salamanders present on all five continents were in decline. Today, the phenomenon of declining amphibian populations affects thousands of species in all types of ecosystems and is thus recognized as one of the most severe examples of the Holocene extinction, with severe implications for global biodiversity.〔(【引用サイトリンク】url=http://www.amphibianark.org/the-crisis/frightening-statistics/ )〕 Since the 1980s, declines in amphibian populations, including population crashes and mass localized extinctions, have been noted 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, and 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. Calculations based on extinction rates suggest that the current extinction rate of amphibians could be 211 times greater than the background extinction rate and the estimate goes up to 25,000–45,000 times if endangered species are also included in the computation. == Background == In the past three decades, declines in populations of amphibians (the class of organisms that includes frogs, toads, salamanders, newts, and caecilians) have occurred worldwide. In 2004, the results were published of the first worldwide assessment of amphibian populations, the Global Amphibian Assessment. This found that 32% of species were globally threatened, at least 43% were experiencing some form of population decrease, and that between 9 and 122 species have become extinct since 1980. , the IUCN Red List, which incorporates the Global Amphibian Assessment and subsequent updates, lists 486 amphibian species as "Critically Endangered". Despite the high risk this group faces, recent evidence suggests the public is growing largely indifferent to this and other environmental problems, posing serious problems for conservationists and environmental workers alike. Habitat loss, disease and climate change are thought to be responsible for the drastic decline in populations in recent years.〔(【引用サイトリンク】url=http://www.conservation.org/learn/biodiversity/species/profiles/amphibians/Pages/overview.aspx )〕 Declines have been particularly intense in the western United States, Central America, South America, eastern Australia and Fiji (although cases of amphibian extinctions have appeared worldwide). While human activities are causing a loss of much of the world’s biodiversity, amphibians appear to be suffering much greater effects than other classes of organism. 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.〔''Science Daily'' (October 15, 2004), (Amphibians in dramatic decline: Study finds nearly one third of species threatened with extinction ). Sciencedaily.com. Retrieved on September 18, 2007.〕 Many scientists believe that amphibians serve as "canaries in a coal mine," and that declines in amphibian populations and species indicate that other groups of animals and plants will soon be at risk.〔 Declines in amphibian populations were first widely recognized in the late 1980s, when a large gathering of herpetologists reported noticing declines in populations in amphibians across the globe. Among these species, the Golden toad (''Bufo periglenes'') endemic to Monteverde, Costa Rica, featured prominently. It was the subject of scientific research until populations suddenly crashed in 1987 and it had disappeared completely by 1989. Other species at Monteverde, including the Monteverde Harlequin Frog (''Atelopus varius''), also disappeared at the same time. Because these species were located in the pristine Monteverde Cloud Forest Reserve, and these extinctions could not be related to local human activities, they raised particular concern among biologists. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Decline in amphibian populations」の詳細全文を読む スポンサード リンク
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