Species Description
The Reticulated and Frosted Flatwoods Salamanders are two species of mole salamander (Genus Ambystoma) native to the southeastern United States. Flatwoods salamanders are relatively small when compared to some other ambystomatid salamanders, reaching a maximum total length of approximately 13 cm (5 in). Like other members of this group, flatwoods salamanders spend most of their lives underground, making many aspects of their ecology and natural history exceptionally difficult to study.
Flatwoods salamanders have a fairly typical pond-breeding amphibian life cycle. Adult salamanders are terrestrial and make annual migrations to breeding wetlands. Eggs are laid in wetland basins before hatching into an aquatic larval stage. Larval salamanders spend several weeks in the aquatic environment before ultimately metamorphosing into terrestrial adults and migrating out of breeding wetlands.
Adult flatwoods salamanders are uniformly black with web-like whitish or gray patterning on the head, back, sides, and tail. This patterning breaks down on the belly and is replaced by scattered white or gray spots. The light patterning on flatwoods salamanders is highly variable and can even be used to identify individuals.
Larval flatwoods salamanders have alternating light and dark stripes that run along the body, helping to camouflage them in their aquatic habitats. Larvae have prominent external gills that are often bright red and a high tail fin to improve their swimming ability. Post-metamorphic salamanders may retain some of the larval striping during the first year of terrestrial life before developing adult coloration and patterning. Size at metamorphosis is variable depending on the amount of time spent in the aquatic environment.
Taxonomy
Flatwoods salamanders were originally described as a single species by Cope in 1868. They were split into two separate, but closely related, species using genetic and morphological data in the mid-2000s. Today, the two species of flatwoods salamander are the Reticulated Flatwoods Salamander (Ambystoma bishopi) and the Frosted Flatwoods Salamander (Ambystoma cingulatum). Both the names Reticulated and Frosted Flatwoods Salamander refer to the light patterning that is characteristic of these species. The scientific name A. bishopi is a reference to the herpetologist Sherman Bishop. The scientific name A. cingulatum comes from the Latin word for ‘girdle’ and is another reference to the patterning along the sides of the salamander. The Ringed Salamander (A. annulatum) is the closest relative of flatwoods salamanders, with all three species grouping together into their own clade.
Distribution
Flatwoods salamanders have an east-west split between the distributions of the two species along the Apalachicola and Flint Rivers. Historically, the combined range of flatwoods salamanders included the Florida Panhandle and southern Alabama, most of southern Georgia and northern Florida, and a portion of coastal South Carolina. Reticulated Flatwoods Salamanders are the western species, while Frosted Flatwoods Salamanders are the eastern species.
Today, the flatwoods salamander range has been dramatically reduced, and both species can only be found at a handful of sites scattered across their historic range. Frosted Flatwoods Salamanders are believed to be extirpated from South Carolina, can only be found at a single site in Georgia (Fort Stewart), and are known from a small number of sites in northern Florida. Similarly, Reticulated Flatwoods Salamanders are believed to be extirpated from Alabama, are known from a single site in Georgia, and can be found at Eglin Air Force Base and adjacent properties in the Florida Panhandle.
Habitat
Flatwoods salamanders inhabit mesic pine flatwoods – a type of longleaf pine forest. These systems are found in low-lying areas of the southeastern U.S. Coastal Plain and are characterized by a matrix of upland and wetland habitats. Wetlands within these systems are typically isolated and lack permanent surface water connections to other water bodies. These wetlands are also ephemeral in nature, meaning that they experience a regular wetting and drying cycle. This prevents predatory fish from becoming established in wetlands and removes a significant amount of predation pressure from larval flatwoods salamanders and other amphibians.
Both upland and wetland habitats are dependent on regular, growing-season fires to maintain the vegetation structure. Pine flatwoods have an overstory of longleaf and slash pines and an understory of thick herbaceous (grasses and forbs) vegetation that is often dominated by wiregrass. Importantly, all flatwoods salamander life stages depend on this herbaceous vegetation to varying degrees. It is used for egg deposition, foraging, and cover.
While little is known about the adult portion of the life cycle, adults are believed to use various underground refugia to shelter from summer temperatures. There have been some observations of flatwoods salamanders associated with crayfish burrows, but adults likely also used small mammal burrows or shelter under other cover objects.
Movement and Home Range
Adult flatwoods salamanders make annual migrations to breeding wetlands from surrounding upland habitats. The vast majority of movement events occur at night and are associated with precipitation. The exact distance that salamanders move to reach breeding wetlands is unknown, but they are likely variable depending on the habitat characteristics. There are reports of flatwoods salamander movements exceeding 1500 m, indicating that some individuals travel long distances to reach breeding wetlands.
Salamanders may remain in breeding wetlands for several months, making short distance movements through the water and over land. At the end of the breeding season, adult salamanders migrate away from breeding wetlands and back into surrounding uplands. It is unclear how adult or juvenile salamanders disperse between breeding wetlands, but multiple studies have indicated that there is a strong relationship between distance and connectivity of breeding wetlands. Wetlands further than 1,500 m apart are unlikely to be linked by the movement of salamanders.
There is no data describing adult movements in their upland habitats. Studies in other ambystomatid salamanders indicate that adults are likely somewhat active in their subterranean retreats for most of the year. Overall, flatwoods salamander home ranges must encompass at least one breeding wetland and enough upland habitat to sustain adult salamanders during the non-breeding season. At a population scale, it is important for habitats to have multiple wetlands in close proximity so that salamanders can disperse between wetlands.
Diet
Little is known about the diet of adult flatwoods salamanders. Adult salamanders are known to eat earthworms but likely consume a variety of other invertebrates encountered in subterranean retreats. It is unclear whether or not adult salamanders feed during the time spent in breeding wetlands. Larval flatwoods salamanders eat a variety of aquatic invertebrates and occasionally consume small vertebrates. Primary prey groups include numerous small crustaceans (Cladocerans, Copepods, Isopods, and Amphipods). Aquatic invertebrates from other groups (Dipterans, Coleopterans, and Hemipterans) may also be consumed but make up a much smaller proportion of the overall diet. Diets of larval salamanders shift as they grow towards larger prey items.
Reproduction
Flatwoods salamanders reproduce in pine flatwoods wetlands that are embedded within surrounding upland forests. Adult salamanders make annual breeding migrations into wetlands, triggered by fall and winter rains during October, November, or December. Once in the breeding wetland, adult salamanders lay eggs in dry portions of the wetland basins, following courtship interactions between male and female salamanders. Eggs are typically laid under vegetation and may be laid individually or in small clumps. A single female salamander can lay over 200 eggs in a breeding season, and there is a positive relationship between female body size and the number of eggs produced.
Eggs hatch once they are inundated by rising water levels. Larval salamanders then remain in the breeding wetland for approximately 11–18 weeks before undergoing metamorphosis. Size at metamorphosis is significantly impacted by the time spent in the wetland environment. The metamorphosis process takes approximately 10 days, and salamanders begin moving away from the breeding wetland immediately after metamorphosing. Young flatwoods salamanders typically leave breeding wetlands from late March through May. In years where larval salamanders reach large sizes, they may be large enough to return to breed in their first year post metamorphosis. However, smaller metamorphs may not return to breed until the second breeding season.
Like many pond-breeding amphibians, flatwoods salamanders are adapted to persist through years with complete reproductive failure due to poor hydrologic conditions within the breeding wetland. Reproductive success is often a complex process where adult movement and egg laying must line up with good hydrologic conditions, which then must persist over the entire larval period. Based on available data, few years have ideal conditions for flatwoods salamander reproduction, and many years are characterized by marginal reproductive conditions.
Conservation Concerns
Flatwoods salamanders have collectively become some of the rarest salamander species in the United States, experiencing precipitous population declines and range contractions. Both species are currently listed on the U.S. Endangered Species List (Reticulated – Endangered; Frosted – Threatened).
The primary driver of flatwoods salamander population declines has been habitat loss and degradation. Many of the historic breeding wetlands no longer exist as natural habitats have been converted to other uses, primarily urban, agriculture, and industrial forestry. Even when wetlands remain intact, uplands across the southeast have been subjected to decades of timber harvest and overall poor management for biodiversity.
One of the major threats currently facing remaining flatwoods salamander populations is habitat degradation due to long-term fire suppression and exclusion. This issue can be observed in both upland and wetland habitats but is often more acute in breeding wetlands because prescribed fires set during the winter often fail to burn through wetland basins. A lack of growing-season fires ultimately leads to the development of shrubby midstory vegetation, which shades out herbaceous vegetation in the wetland basin. Once wetlands lose their herbaceous vegetation layer, salamanders no longer have access to high-quality egg laying and larval habitats.
It is possible to reverse the negative effects of vegetation change through good management practices. However, this is a labor and time intensive process. Woody vegetation can be removed from breeding wetlands through a combination of mechanical (chainsaw) removal and herbicide applications. Once the midstory vegetation is removed application of prescribed fire can be targeted towards dry wetland basins to promote herbaceous vegetation growth. Accumulated duff layers can also be removed manually to further speed up this process. It is worth noting that even after initial vegetation treatment (to remove woody vegetation) follow up treatments are needed to ensure that wetlands do not revert back to a degraded state. Ultimately, wetlands must be managed over the long-term through some combination of prescribed fire and manual vegetation control to maintain appropriate vegetation structures for flatwoods salamanders.
Another significant factor contributing to flatwoods salamander declines has been poor reproductive success during severe droughts. In such cases, some populations can experience consecutive years of complete reproductive failure, which is thought to have contributed to some of the observed population declines on protected lands. Furthermore, research has indicated that wetland hydroperiods (the length of time that wetlands hold water) have been shorter in recent years than they were historically. The effects of climate change have been implicated in overall poor reproductive conditions for flatwoods salamanders, and few years in the coming decades are likely to have high-quality breeding conditions.
There have been some positive developments surrounding flatwoods salamander conservation in recent years. On Eglin Air Force Base in the Florida Panhandle, extensive habitat management in breeding wetlands has led to an increase in the number of known occupied breeding sites in recent years. Such habitat improvements are also likely to lead to larger population sizes as more habitat becomes suitable for salamanders. This can make populations more resilient to some of the other potential threats. Another exciting development has been the short-term success of salamander translocations on Eglin Air Force Base. This work is aimed at restoring populations to areas where they have been extirpated and are unlikely to recolonize on their own. While the long-term success of this work is still in question, such efforts could significantly increase the speed at which populations can be restored.
Overall, flatwoods salamanders will continue to be restricted to a handful of mostly publicly-owned properties for the foreseeable future. Persistence of known populations is predicated on high-quality management of both breeding wetlands and surrounding uplands. Long-term research and monitoring programs will continue to provide important insights into flatwoods salamander ecology and conservation. Captive breeding efforts may eventually contribute to restoration of the species across its range, particularly efforts to restore populations in Alabama or South Carolina. Flatwoods salamanders ultimately face an uncertain future that exemplifies many of the challenges facing the successful conservation of herpetofauna in the southeastern United States.