Ecotoxicology 2, 65-77 (1993) The effects of acid precipitation on amphibians BENJAMIN A. PIERCE Department of Biology, Baylor University, Waco, TX 76798-7388, USA Received 4 August 1992; accepted 11 September 1992 A large number of studies conclusively demonstrate that low pH conditions have important ecological effects on amphibian communities. These effects vary developmentally and depend on complex interactions with other physical, chemical, and biological parameters. Acid sensitivity varies widely within and among species of amphibians. In spite of the importance of acidity to their reproductive success and the presence of many acidic amphibian habitats, there is, at present, little direct evidence that acid precipitation has produced widespread declines in amphibian popula- tions. However, the potential role of sublethal effects of acidity on amphibian declines has not been studied thoroughly. Keywords: acid precipitation; acid tolerance; amphibians; embryos; frogs; salamanders; tadpoles Introduction Although the smallest class of vertebrates in number of species, amphibians are critical components of many natural ecosystems, a fact that is frequently unappreciated because of their secretive habits. For example, tadpoles regulate the algal composition of ponds (Dickman, 1968; Seale, 1980), and terrestrial salamanders may comprise a major portion of animal biomass in some forests (Burton and Likens, 1975). Amphibians are also a major source of nutrient flow from aquatic to terrestrial habitats. In recent years, there has been growing interest in the ecology of amphibians in low pH environments. This research has been stimulated by concerns about the deleterious effects of acid precipitation on amphibian communities (Pough, 1976) and by recent reports of worldwide declines in amphibian populations (Barinaga, 1990; Wake, 1991). Although a link between widespread declines and acid precipitation has yet to be established, there are important reasons to believe that amphibians may be particularly vulnerable to acid rain. First, many amphibians utilize ephemeral aquatic habitats, which periodically dry and refill with fresh precipitation. These ponds typically occupy small watersheds, and the water entering them has limited contact with the soil and other buffering systems. Furthermore, the ponds themselves are frequently low in calcium and alkalinity (Freda et al., 1991). For these reasons, amphibian habitats may be influenced strongly by precipitation chemistry, and may be susceptible to acidification from acid deposition. Amphibians are also susceptible to acid precipitation because of the timing of their reproduction. Early embryological stages are most sensitive to acidity (Pierce et al., 1984; Freda, 1986), and many species breed in early spring, when aquatic habitats are lowest in pH and alkalinity (Pierce et al., 1984; Freda and Dunson, 1985a; Freda et al., 0963-9292© 1993Chapman & Hall