Amphibians

Two orders of amphibians are present in the Southern United States: Caudata (salamanders) and Anurans (frogs and toads). The South supports the highest density of amphibian species in North America (Echternacht and Harris 1993). The total includes 107 salamanders and 63 species of frogs and toads (fig. 5.4). In individual States, the number of amphibian species ranges from 80 in North Carolina to 49 in Arkansas (NatureServe 2000). Numbers in other States are 77 in Georgia, 75 in Texas, 73 in Virginia, and 70 in Tennessee.

The Southern Appalachians have an unusually large number of salamander species, because many plethodontid species evolved there. These lungless animals are believed to have evolved in fast-flowing, oxygenated streams. The numbers of salamanders inhabiting North Carolina (50), Virginia (48), Tennessee (48), and Georgia (44) reflect the importance of the Appalachian Mountains. The number of salamanders occurring in the Coastal Plain is lower because habitat and temperature are less suitable and because densities of terrestrial and aquatic predators are higher (Echternacht and Harris 1993).

Numbers of frogs and toads are highest in the southernmost Coastal States. Numbers of species are 43 in Texas, 33 in Georgia, 32 in Florida, 31 in Louisiana, 31 in South Carolina, and 30 in Alabama (NatureServe 2000). The majority of southern species are in five families: true frogs; tree, chorus, and cricket frogs; true toads; narrowmouth toads; and spadefoot toads. Eleven species are endemic to the South (Echternacht and Harris 1993).

Seven species of amphibians are listed as threatened or endangered by the U.S. Fish and Wildlife Service (table 5.4). In addition, several amphibians are classified as imperiled or vulnerable by the Natural Heritage agencies (chapter 1).

Amphibians have complex life cycles and inhabit a variety of environments. Habitats include ephemeral pools, caves, forests, wetlands, savannas, and several aquatic habitats. The longleaf pine-wiregrass community, cypress-gum swamps, isolated wetlands, and mixed hardwood-pine habitats support a diversity of species. The federally listed flatwoods salamander is found in the longleaf pine-wiregrass ecosystem. Coastal Plain forests provide habitat for ambystomatid species. In even greater abundance in the South are the many species of tree frogs, toads, and other frogs. Pine barrens tree frogs occur in Coastal Plain forests from Alabama northwards (Gibbons and Buhlmann 2001).

Amphibians are very different physiologically from reptiles, but the two groups are classified together as herpetofauna. Amphibians are more restricted by environmental moisture than other terrestrial vertebrates. They depend on areas where there is sufficient moisture for reproduction and survival. Since the glandular thin skin of amphibians is permeable to water, evaporative water loss is a serious problem. In addition, drought affects egg laying and larvae survival. The demands of water balance and thermoregulation may restrict movement, which occurs in a narrow range of environmental conditions.

Many amphibian species have geographic ranges that are restricted to particular physiographic regions. Some salamander species are considered glacial relicts that were isolated on mountaintops that retained northern climates (Gibbons and Buhlmann 2001). Similarly, frog species such as the pine barrens tree frog, Houston toad, and Florida bog frog occur in small, isolated populations throughout their ranges. The distances between such disjunct populations make recolonization difficult.

Salamanders—The majority of southern salamanders are in six families: mole salamanders, amphiumas, hellbenders, lungless salamanders, waterdogs or mudpuppies, and sirens. Salamanders are inconspicuous species that are important components of the forest ecosystem. They are small, secretive, and primarily nocturnal. They range from 5 cm to over 1 m in length. Limited data suggest that generation times are relatively long. For example, the generation times for several species of salamanders range between 4.4 and 9.5 years.

The rate of reproduction in amphibians is highly variable, but many species exhibit low frequencies of reproduction. Often salamanders breed only in alternate years, when they lay a single clutch of eggs.

Moisture is a limiting factor for all salamander species. Some species are totally aquatic, but even the terrestrial species can only survive in moist microhabitats. Ambystoma and Hemidactylus salamanders require moist, friable soils for burrowing. Several terrestrial species migrate to aquatic habitats for egg deposition, while others require damp microhabitats. In addition, some aquatic species use terrestrial habitat for dispersal and other seasonal activity.

Salamanders inhabit areas with a variety of physiographic features, but rivers, streams, and stream margins figure prominently in their occurrence (table 5.5). Coastal bayous, ponds, and slow-moving rivers support sirens and amphiumas, while the hellbender occurs in cooler, fast-flowing upland rivers.

Leaf litter, fallen logs, moist soils, and other surface debris serve as refuges from drying conditions. The ringed and streamside salamanders use moist soil, while the flatwoods and Jefferson salamanders use leaf litter. Fallen logs provide an important habitat component for the marbled and mole salamanders. Several species, including the spotted and Mabee’s salamanders, also prefer closed-canopy conditions adjacent to water sources.

Table 5.6 shows the associations between 23 vegetative cover types (following Hamel 1992) and salamanders in the South. Mesic, mixed pine, and hardwood forests support 72 percent of species, including ringed, marbled, and mole salamanders. Sixty-four percent of the salamanders occupy mesic, upland hardwoods. These species include streamside, smallmouth, seepage, and dusky salamanders. White pine-hemlock and bottomland forests are used by slightly less than half of the southern salamanders. Jefferson, spotted, and green salamanders occupy white pine-hemlock forests, while several amphiuma species are found in bottomland hardwood forests. Xeric oak-hickory forests also support a variety of salamanders.

Salamander diversity appears to be less on the Coastal Plain than in the Appalachian Mountains. The former has much sandy, well-drained soil, high summer temperatures, and higher densities of predators (Echternacht and Harris 1993).

Connectivity between preferred forest habitats reduces population isolation and promotes dispersal (Wilson 1995), a management concern for many amphibian species. Many salamanders are adapted to travel only short distances in response to habitat alteration, while others with restricted geographic ranges become imperiled if habitat modification is rapid enough to preclude dispersal to similar habitats (Gibbons and Buhlmann 2001).

Table 5.7 illustrates relationships between salamander occurrence and forest successional stage. The seral stages follow those used by Hamel (1992): grass-forb, seedling-sapling, poletimber, and sawtimber. Note that not all cover types contain each seral stage. The Everglades type, for example, only exists in the grass-forb stages. Most salamander species find optimum habitat conditions in sawtimber stands.

Frogs and toads—The South is inhabited by numerous species of frogs and toads, each with its own particular requirements. The region supports such diversity due to its warm, humid climate, diversity of vegetative communities, and abundance of aquatic environments, particularly wetlands.

Wilson (1995) places these species into: (1) terrestrial species that migrate to standing water for egg deposition, (2) semiaquatic species requiring terrestrial habitat for dispersal, and (3) aquatic species that may use terrestrial habitat during rainy conditions. Each species requires standing water for egg deposition and larval development.

Several species exhibit two distinct stages: an aquatic larval stage (tadpole) and an adult stage. The eggs develop into tadpoles, which then undergo a complex metamorphosis into adults. The two stages have different habitat requirements that influence distributions and habitat associations.

Tadpoles consume algae and bacteria, while adult frogs and toads rely upon invertebrates. Some species, such as the pig frog, remain semiaquatic as adults, while others become terrestrial. Frogs and toads are important prey for wading birds, raptors, foxes, raccoons, and snakes.

Moisture also is a limiting factor for most frog and toad species; even terrestrial species require moist microhabitat (table 5.5). In addition to broad stream margins, frequently used habitats include both permanent and seasonal swamps and ponds. Many species, including the American toad and southern cricket frog, require moist soils for burrowing.

Leaf litter, potholes, and aquatic vegetation often provide moisture (table 5.5). The oak toad and pine barrens tree frog use leaf litter, while the southern chorus frog and the bird-voiced tree frog use aquatic vegetation. Potholes provide an important habitat component for Brimley’s chorus and southern leopard frogs (Wilson 1995). Species that prefer open-canopy conditions include the Houston toad and the northern cricket frog.

Although wetlands are important breeding habitats, many frog and toad species spend part or all of their nonbreeding season in trees and shrubs. Forest structure creates diverse habitats with many niches. Forests also contribute organic matter and moderate the temperature and evaporation rate of adjacent aquatic habitats.

Southern frogs and toads inhabit a wide variety of forest cover types (table 5.6). Mesic, mixed pine and hardwood forests support 83 percent of species, including the American toad, Cope’s gray tree frog, and northern cricket frog. Seventy-eight percent of the species inhabit bottomland hardwood forests, including Woodhouse’s toads, pine woods tree frogs, squirrel tree frogs, and gray tree frogs. Longleaf pine, cypress-tupelo, and bay-pocosin habitats are used by over half of the frog species in the region. Oak and southern toads and southern cricket frogs occupy longleaf pine forests, while several tree frogs are characteristic of cypress-tupelo associations. It appears that a majority of species finds optimum and suitable habitat conditions in the grass, sapling, and poletimber stages (table 5.7).

Habitat management for amphibians—The complex life cycle of frogs and toads requires management of both terrestrial and aquatic habitats. Tiger salamanders and other ambystomas breed in the water but remain terrestrial during nonbreeding season. Thus, providing only one habitat component would fail to maintain viable populations of these species. Some terrestrial species require ponds or other standing water during the breeding season. Consequently, the removal of barriers such as roads between terrestrial habitat and aquatic habitat is important.

The semiaquatic species require aquatic areas that have rocks, woody debris, or other similar shelter in the water. Emergent and floating vegetation is important for breeding of some species. The adjacent terrestrial habitat also is important because many species, such as the Eurycea and Desmognathus genera, spend significant portions of their lives foraging and occupying terrestrial areas. Buffers adjacent to streams provide access to upland forested habitats. Aquatic habitats should be protected against thermal changes, water pollution, and excessive siltation (Wilson 1995). Habitat alteration due to dredging, channelization, and impoundment can be detrimental to many species.

Forest management alters the vegetative composition, seral stage, and structure of amphibian habitat. For example, prescribed burning temporarily removes leaf litter, herbaceous cover, and woody understory vegetation. Vegetative structure, snags, loose bark, and surface debris are important factors in managing amphibian habitat. Disking, windrowing, and furrowing during some forestry operations (Gibbons and Buhlmann 2001) may negatively impact species dependent upon the understory. Conversion from one forest type to another may be beneficial to some species and detrimental to others. The change in successional stage from sawtimber to grass-forb that results from timber harvest may enhance habitat suitability for one species, yet create marginal habitat for another.

Amphibian declines—Reported declines of amphibian populations have drawn considerable attention over the past two decades. Many are associated with high elevation, pristine areas that are remote from surrounding landscape modification. Amphibians are particularly sensitive to their environment. Their permeable skin and the lack of protective eggshells make them vulnerable to toxicants present in soil and water.

Southern species showing evidence of declines include the flatwoods salamander, Red Hills salamander, Texas blind salamander, wood frog, southern dusky salamander, and green salamander. Numerous others are categorized as imperiled and vulnerable (chapter 1). Endemic species are of particular concern in the Edwards Plateau, Ozark Highlands, Atlantic Coastal Plain, and Appalachian Mountains.

Amphibian declines have been attributed to several factors. These include habitat loss, wetland alteration, climate changes leading to droughts, diseases, exotic species, and agricultural chemicals. Other factors include acid precipitation and ultraviolet radiation. These are briefly reviewed later.

Wetlands and vernal pools are important for several amphibians. There have been significant losses of wetlands in the last two centuries (chapter 1). Declines in wetland quality through eutrophication, pollution, and fish stocking also impact amphibian populations. The hellbender is affected by stream degradation, while the gopher frog is influenced by the conversion of pine and hardwood forests to tree plantations, agriculture, and urban uses. In addition, habitat fragmentation by roads contributes to the mortality of breeding adults and dispersing juveniles (Wilson 1995).

Ozone depletion in the upper atmosphere increases the amount of ultraviolet radiation on the Earth’s surface, particularly at high elevations. Ambient radiation damages cellular DNA (Reaser and Johnson 1997); amphibians with low levels of photolyase enzyme have embryos that are susceptible to ultraviolet radiation, which causes mortality and abnormal development, including skeletal, eye, and skin deformities.

Their porous skin makes amphibians susceptible to herbicides, pesticides, heavy metals, and petroleum products in aquatic systems. Pollutants such as gasoline, oil, and antifreeze sometimes occur in runoff into amphibian habitat. Relatively high nitrate levels cause physical and behavioral abnormalities in a number of species; synthetic chemicals interfere with hormonal processes, inhibiting amphibian development (Reaser 1996). The application of fertilizers and pesticides, particularly by aerial spraying, often impacts amphibians far from the point of application in nontarget areas.

The introduction of exotic species, such as fish, crayfish, and bullfrogs, into lakes and wetlands also influences amphibian populations. Fish introduced into wetlands for mosquito control prey upon amphibian eggs and larvae. Chytrid fungi, trematode parasites, and viruses carried by exotic fish may also contribute to population declines.

Several of the factors discussed above have been implicated as causes of amphibian abnormalities. These include parasite infestation, toxin contamination, radiation, radioactive salts, ground-level ozone, excessive heating of eggs, and reformulated gasoline (Reaser and Johnson 1997). Of these, only the parasite, toxin, radiation, and predation hypotheses have supportive evidence. The frequency of malformations is highest in frogs that have recently metamorphosed from tadpoles.

Concern about the status of amphibian populations is clearly warranted. Physiological constraints, limited mobility, and changes in site characteristics hinder recolonization of sites of local extinction. The temporal and spatial population dynamics of many amphibians are not well understood; it is unknown whether observed declines exceed natural population fluctuation.

There are other concerns facing individual amphibian species. Many of these are discussed in the section on reptiles, as these concerns are shared by herpetofauna as a group. In addition, some of these concerns are mentioned in Species accounts presented next.

Species accounts—The following are accounts for selected amphibian species that are of concern in the South. Several are federally listed as threatened or endangered. Others are classified as imperiled or vulnerable by Natural Heritage agencies. The species accounts and management recommendations follow Wilson (1995) unless otherwise noted.

Species accounts: flatwoods salamander—The population of this threatened species has declined during the past 10 to 15 years (Wilson 1995). The cause of the decline is uncertain, and the salamander is uncommon throughout its range from South Carolina, southern Georgia, and Florida westward to Mississippi.

The salamander inhabits pine flatwoods dominated by longleaf and slash pines and wiregrass, which is important for egg disposition. It is often found in association with cypress ponds, swamps, and pitcher plant bogs that are used for reproduction.

Management activities focus on avoidance of intensive site preparation before harvest, avoidance of prescribed burning during peak surface activity and breeding periods (November through April), and protection of breeding ponds. Fish stocking should be avoided (Bury and others 1980).

Species accounts: Florida bog frog—This species is classified as imperiled by Natural Heritage and is a species of special concern in Florida (NatureServe 2000). The frog is currently known to exist in 23 localities in the Panhandle (Moler 1992b). Many are found on the Eglin Air Force Base.

This frog species inhabits nonstagnant acidic seeps and the shallow backwaters of larger streams. It is frequently found in association with sphagnum moss and early seral stages of Atlantic white-cedar. Shrubby streamside habitats that do not have developing hardwood forests are preferred. The frog’s diet consists of insects and other small arthropods.

Stream contamination and impoundment, and forest succession threaten the survival of this species (Moler 1992b). Conservation actions center on the protection of suitable habitat. Management of streamside vegetation to maintain the shrub-bog community is advised.

Species accounts: gopher frog—This uncommon species is classified as vulnerable by Natural Heritage (NatureServe 2000). Alabama, Florida, Georgia, Mississippi, North Carolina, and South Carolina list the frog as of special concern. The gopher frog historically was distributed along the Gulf and Atlantic Coastal Plain, with isolated populations in the Valley and Ridge Province of Alabama. It was last documented from Louisiana in the 1960s. The frog has declined throughout its range with the loss of longleaf pine habitat (Martof and others 1980).

The gopher frog is associated with sandy pine flatwoods, turkey oak-pine sandhills, and xeric hammocks. It breeds in shallow, temporary ponds with open canopies and emergent herbaceous vegetation. Ditches and borrow pits are occasionally used. Adults seek refuge in the burrows of gopher tortoises, mice, and crayfish. Stump holes, root mounds, dense grass clumps, and thick mats of leaf litter may also be used.

The frog is an opportunistic feeder with a diet of arthropods, small frogs, and toads. Predators include water snakes, turtles, bluegills, and mosquitofish.

Management centers on protection of the sandhills and scrub-oak ecosystems and halting the losses of this habitat to circular irrigation farming and industrial development. Prescribed burning and other management practices that retain the open scrub nature of this habitat benefit this species (Wilson 1995), while practices that drain or alter breeding ponds are detrimental.

Species accounts: green salamander—This species is classified as vulnerable by Natural Heritage and is a species of special concern in Alabama, Georgia, Mississippi, and North Carolina (NatureServe 2000). Impoundment of several rivers in the Carolinas has extirpated several known populations.

The unique habitat of this species is limited and localized. The green salamander lives in damp crevices in shaded rock outcrops and under the bark of cove hardwood trees. It also is found in upland areas of Virginia pine and white pine-hemlock with mountain laurel understories. The salamander’s diet consists of small insects, spiders, and earthworms.

Conservation efforts focus on protection of rock outcrops and the establishment of buffer zones in areas of timber harvest.

Species accounts: Houston toad—This endangered species is restricted to southeastern Texas, where its population is very small and fragmented. Human alteration of natural watersheds has eliminated many of its natural breeding pools, resulting in hybridization with the Gulf Coast toad and the Woodhouse’s toad (Wilson 1995).

This toad inhabits areas with sandy, friable soils and is found most often in loblolly pine or mixed deciduous habitats interspersed with grassy areas under a range of conditions. Breeding habitats include roadside ditches, temporary ponds, and other seasonally flooded low spots. The toad’s diet consists primarily of insects.

The recovery plan requires protection of critical habitat for this species. Habitat is maintained in a pristine state, and several breeding projects have been attempted. Development projects have been regulated in areas designated as critical habitat (Brown 1975).

Species accounts: one-toed amphiuma—This species is classified as vulnerable by Natural Heritage and listed as rare in Georgia (NatureServe 2000). It occurs in restricted geographic areas in northern Florida, Mobile Bay in Alabama, and the Ochlocknee River drainage in Georgia.

This semiaquatic salamander requires mucky habitats in association with permanent streams (Means 1992). Management actions center on protection of muck areas, which are threatened by sand and silt sedimentation during construction activities. Other actions include the regulation of amphiuma collection.

Species accounts: Red Hills salamander—This species is listed as threatened at both the Federal and State level. It is confined to a narrow belt within the Tallahatta and Hatchetigbee geological formations in the Red Hills of Alabama (Wilson 1995).

This nocturnal salamander lives in burrows on high, steep, uncut slopes with high soil moisture content and full tree canopy (Dodd 1991). The burrows are often near the base of a tree or under siltstone outcroppings. The salamander feeds on spiders and insects (U.S. Fish and Wildlife Service 1983, 1990b).

The majority of land in its range is privately owned. Habitat has been reduced by timber harvest, conversion of forest to agriculture, and ridgetop clearing. Overcollecting may have caused a decline in some areas. Feral hogs are a threat in localized areas (NatureServe 2001).

Conservation actions include cooperation with private and corporate landholders to restrict clearcutting and heavy site disturbance. Under public ownership, two areas have been set aside to support limited populations (NatureServe 2001). These include Alabama Forestry Commission and U.S. Army Corps of Engineers lands. In 1991, International Paper Company initiated work on a Habitat Conservation Plan (HCP) for this species. Other companies subsequently developed HCPs (Bailey 1995). Research needs include determination of the microhabitat effects of timber management practices and the collection of data on reproductive viability and recruitment within existing populations.

Species accounts: Shenandoah salamander—This species is endangered due to restricted range, habitat modification, and competitive interactions with the redback salamander. Inhabiting the high-elevation mountains of Virginia, the species requires talus slopes with deep soil pockets in mixed coniferous and deciduous forests. Its diet consists of small arthropods and earthworms.

Conservation efforts include restriction of construction activities that could disturb the limited talus habitats of this salamander (Martof and others 1980). Any construction of trails, roads, or overlooks in the Shenandoah National Park should be carefully monitored so as not to impact this salamander’s limited habitat.

Species accounts: Tennessee cave salamander—This species is classified as imperiled by Natural Heritage and is listed as endangered in the States of Alabama and Tennessee (NatureServe 2000). The salamander is found in permanent streams and pools in limestone caves of central and southwest Tennessee, northern Alabama, and extreme northwest Georgia. It is believed to occur in approximately 1 percent of the caves in its range.

The Tennessee cave salamander feeds on arthropods, other small aquatic insects, and earthworms. Management centers on restricting human access and protecting limestone cave habitat. The species is very sensitive to pollutants and disturbances within its habitat (Wilson 1995).