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 extinction 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.