Amphibians (class Amphibia)

Amphibians of the Southeastern United States

(Authored by J.D. Willson, Brian Todd, and J. Whitfield Gibbons - Savannah River Ecology Laboratory Herpetology Program)

The southeastern United States is the epicenter of amphibian biodiversity in North America, perhaps due in part to the high diversity of terrestrial and aquatic habitats found in the region. The southern Appalachians region is particularly noted for its high biodiversity of salamanders, many of which are not found anywhere else. Salamanders found in the region range from the tiny pigmy salamander (Desmognathus aeneus), which is seldom more than two inches long, to the bizarre and prehistoric-looking hellbender (Cryptobranchus alleganiensis), which can exceed two feet in length and lives primarily under rocks in swift-flowing mountain streams. The Coastal Plain regions of Mississippi and Alabama are home to the eel-like giant salamanders, Siren and Amphuima, while many plethodontids, a group of terrestrial and stream-dwelling lungless salamanders, can be found on the peaks of the highest Southeastern mountains. One introduced exotic species, the greenhouse frog (Eleutherodactylus planirostris) is found in the Gulf Coast regions of Mississippi.

Although not as diverse as the salamanders, few habitats exist in the Southeast that are not home to several species of frogs, toads, and treefrogs. Calls of some species, such as the wood frog (Rana sylvatica) and spring peeper (Pseudacris crucifer) are anticipated by many as the first harbingers of spring. Other species, such as the rare gopher frog (Rana servosa) and spadefoot toad (Scaphiopus holbrookii), spend nearly all their time buried deep underground, only emerging to breed on a few rainy nights each year.

Ecological Significance of Amphibians
In the southeastern United States, amphibians comprise a substantial proportion of vertebrate biodiversity in nearly every habitat type. Perhaps more importantly, however, amphibians play important functional roles in many ecosystems. Although most amphibian species are seldom seen because of their cryptic behavior and low activity levels, recent research has shown that amphibians can be extraordinarily abundant in many habitats. For example, an often-cited study demonstrated that the biomass of redback salamanders (Plethodon cinereus) inhabiting a New Hampshire was more than twice that of breeding birds was roughly equal to the biomass of small mammals (Burton and Likens 1975). Similarly, a study conducted by the Savannah River Ecology Laboratory in South Carolina documented the production of over 400,000 newly-metamorphosed frogs, toads, and salamanders from a single 10 hectare wetland over the course of a year (Gibbons et al. 2006). The Southern Appalachian region is remarkable for its salamanders, both in terms of species diversity and absolute abundance. In fact, terrestrial salamander densities are estimated to reach at least 18,000 per hectare in Appalachian streamside forests (Petranka and Murray 2001). At such densities, salamanders undoubtedly serve as important predators and prey for a variety of other organisms, making them important contributors to ecosystem processes such as energy transfer and nutrient cycling (reviewed in Davic and Welsh 2004).

Susceptibility of Amphibians to Environmental Degradation
Recently, catastrophic declines in amphibian populations and species have been reported world-wide. Indeed, amphibians are currently considered the most globally-imperiled vertebrate group with 35% of species being threatened (vulnerable, endangered, or critically endangered) and 43% experiencing population declines, according to IUCN Red List criteria (Stuart et al. 2004). Causes for global amphibian declines include emerging diseases, global climate change, habitat destruction and degradation, environmental contamination, unsustainable use (including harvest for the pet or food trade and road mortality), and invasive exotic species (Semlitsch 2003a). Of these factors, habitat degradation is considered by many researches to be the single greatest threat to amphibians, both world-wide and in the Southeast specifically. The permeable skin possessed by amphibians, through which many species absorb water and air, also allows easy uptake of contaminants and other pollutants. Most amphibian species have both aquatic and terrestrial life stages. Further, amphibians are unique in that most species move extensively between aquatic and terrestrial habitats as they complete various stages of their lives. Thus, amphibians are not only vulnerable to degradation of both aquatic and terrestrial habitats, but require intact corridors that allow movement between the two habitats. Indeed, numerous studies have shown that preservation of aquatic breeding habitat, alone, is not sufficient to preserve amphibian populations. Nearly all species studied require extensive terrestrial buffers around aquatic habitats in order to maintain viable populations (Semlitsch 1998, Willson and Dorcas 2004). Finally, the reliance of many amphibian species on fishless seasonal wetlands for reproduction has lead to dramatic declines in many taxa. These types of wetlands currently receive no federal protection and thus are often destroyed or modified (stocked with gamefish, for example), making them unsuitable as amphibian breeding sites (Semlitsch 2003b). The impacts of humans on amphibians is not restricted to rare or uncommon species. A recent study estimated that common stream-dwelling salamanders had declined by 20-45% in the last three decades due to urbanization and associated land conversion in the Piedmont region of the eastern United States (Price et al. 2006).

Works Cited
Burton, T. M. and G. E. Likens. 1975. Salamander populations and biomass in Hubbard Brook Experimental Forest, New Hampshire. Copeia:541-546.

Davic, R. D. and H. H. Welsh. 2004. On the ecological roles of salamanders. Annual Review of Ecology Evolution and Systematics 35:405-434.

Gibbons, J. W., C. T. Winne, D. E. Scott, J. D. Willson, X. Glaudas, K. M. Andrews, B. D. Todd, L. A. Fedewa, L. Wilkinson, R. N. Tsaliagos, S. J. Harper, J. L. Greene, T. D. Tuberville, B. S. Metts, M. E. Dorcast, J. P. Nestor, C. A. Young, T. Akre, R. N. Reed, K. A. Buhlmann, J. Norman, D. A. Croshaw, C. Hagen, and B. B. Rothermel. 2006. Remarkable amphibian biomass and abundance in an isolated wetland: Implications for wetland conservation. Conservation Biology 20:1457-1465.

Petranka, J. W. and S. S. Murray. 2001. Effectiveness of removal sampling for determining salamander density and biomass: A case study in an Appalachian streamside community. Journal of Herpetology 35:36-44.

Price, S. J., M. E. Dorcas, A. L. Gallant, R. W. Klaver, and J. D. Willson. 2006. Three decades of urbanization: estimating the impact of land-cover change on stream salamander populations. Biological Conservation 133:436-441.

Semlitsch, R. D. 1998. Biological delineation of terrestrial buffer zones for pond-breeding salamanders. Conservation Biology 12:1113-1119.

Semlitsch, R. D. 2003a. General threats to amphibians. Pages 1-7 in R. D. Semlitsch, editor. Amphibian Conservation. Smithsonian Institution, Washington D. C.

Semlitsch, R. D. 2003b. Conservation of pond-breeding amphibians. Pages 8-23 in R. D. Semlitsch, editor. Amphibian Conservation. Smithsonian Institution, Washington D. C.

Stuart, S. N., J. S. Chanson, N. A. Cox, B. E. Young, A. S. L. Rodrigues, D. L. Fischman, and R. W. Waller. 2004. Status and trends of amphibian declines and extinctions worldwide. Science 306:1783-1786.

Willson, J. D. and M. E. Dorcas. 2003. Effects of habitat disturbance on stream salamanders: implications for buffer zones and watershed management. Conservation Biology 17:763-771.

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Reaser, J. K. (2000). Amphibian declines: an issue overview. Federal Taskforce on Amphibian Declines and Deformities,Washington, DC. Retrieved March 17, 2008 from http://www.frogweb.gov/declines.pdf.

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