Christine A. Bishop | Geology Reports

USGS2010

Recent advancements in amphibian ecotoxicology

When the first edition of Ecotoxicology of Amphibians and Reptiles was published in 2000, I reviewed the state of the literature from 1972 through 1998 (Sparling et al. 2000). That review covered 11 271 contaminant citations listed in Wildlife Review and Sports Fisheries Abstracts published by the US Fish and Wildlife Service. Among its findings, only 2.7% of the cited papers were on amphibians and 1.4% on reptiles. This equated to an average annual rate of 11.5 citations for amphibians and 6 for reptiles, although the distribution of citations was not homogeneous through the years. In contrast, 61.8%, or 280, contaminant citations per year were on fish. Among the amphibian citations, most focused on effects, 23% dealt with metals, 22% with acid precipitation, and 19% with nonchlorinated pesticides. The remaining 38% covered all of the other contaminants of interest at that time. Almost all of the citations on reptiles dealt exclusively with residues, and turtles (Chelonia) were overrepresented compared to the percent of reptilian species comprised by this order. The most important categories of contaminants included metals (24%), organochlorine pesticides (23%), and polychlorinated biphenyls (PCBs) (19%), all persistent pollutants.

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USGS2003

Physical habitat and its alteration: A common ground for exposure of amphibians to environmental stressors

Amphibians as a class of vertebrates have persisted for hundreds of millions of years (Stebbins and Cohen 1995), but they are currently threatened by a variety of stressors, many resulting from human-related alterations of the environment. Most species of amphibians live closely associated with moist environments throughout their life and have evolved specialized adaptations that conserve water and reduce desiccation (Stebbins and Cohen 1995; Henry 2000; Chapter 2A). Amphibians are ectotherms, so their body temperatures fluctuate with the local environment. Latitude, elevation, and habitat affect environmental temperature and have a strong influence on amphibian distributions. Despite these physiological and habitat constraints, the 4750 species of amphibians in the world today have exploited a wide variety of habitats that range from dry deserts to tropical rain forests and from sea level to elevations above 4000 m (McDairmid and Mitchell 2000). The direct loss of suitable habitat has had a profound effect on amphibian populations (Johnson 1992), as it has on nearly all species of wildlife. In the U.S., 53% of wetlands have been lost to human development in the last 200 years (Dahl 1990). Similar loss of wetlands has occurred throughout much of the world, especially in developing countries (Miller 1993). In many regions, deforestation has reduced or eliminated suitable terrestrial habitats, and this may prove to be the largest global threat to amphibian populations (Johnson 1992). Eight thousand years ago, forests covered approximately 40% of the world’s land (6 billion hectares), but by 1997, the world’s forests had been reduced to 3.5 billion hectares, a 42% loss worldwide (CIDA 2001). The effect of habitat loss is generally both obvious and predictable; with increasing restriction of suitable habitat, amphibian populations will probably not survive. The anthropogenic effects on the quality of the habitat that remains are often less obvious.

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