The Herpetology Lab at the Jones Center addresses questions related to the management and conservation of amphibians and reptiles in the species-rich longleaf pine ecosystem.
The longleaf pine forest, embedded seasonal wetlands, and perennial streams at Ichauway support 30 species of amphibians and 53 reptiles, including 9 species of conservation concern such as the gopher tortoise, and 1 game species, the American alligator (Pub 1). Approximately 50% of the herpetofaunal species of Georgia occur at Ichauway (and 60% of the state’s coastal plain species). The diversity of vegetation communities and our conservation management program offer a unique opportunity for research on these understudied species.
Predator Ecology and Management in Longleaf Pine Ecosystem
Predators are of interest in the southeastern U.S. because of concerns about their impacts on game species and rare, threatened, and endangered species. However, predator-prey interactions are complex. For example, as a group, snakes are often perceived negatively because some snake species depredate gamebirds and their eggs. But snake predators include at least 5 species, none of which were the top predator of shrub-nesting songbirds in a 2010 study (Pub 2). Often overlooked is the fact that snakes are important predators of other species like cotton rats, which depredate gamebird nests. Few studies have focused on the complexity of predator-prey interactions and the effects of predators on non-game species, such as the gopher tortoise. Thus, we are collaborating with the Jones Center Wildlife lab on a long-term study on predator ecology.
Our research extends across Ichauway as well as in experimental plots where we have manipulated predator abundance. This approach has allowed us to examine the effects of mammalian predation on the gopher tortoise, to identify and study the effects of other predators, like the red-imported fire ant, on herpetofauna, and to better understand the natural history of snakes as important predators in the longleaf pine ecosystem. Individual research studies are outlined below.
Gopher tortoises and predation
Gopher tortoises are long-lived vertebrates that inhabit below-ground burrows. Although we do not know exactly how long they live, it is likely upwards of 60-80 years. Although they are slow to reach reproductive maturity (15-20 years old) and have a low annual reproductive output (~6-7 eggs/year), in a stable environment this is compensated by high adult survival and their long reproductive life-span (potentially 40 years!). Adult gopher tortoises have a thick protective shell. But gopher tortoise eggs and juveniles are vulnerable to predation by mammals; eggs are deposited in shallow nests below ground, and juveniles are small and have a soft shell that does not protect them from predators.
- Changes in predator communities in the southeastern U.S. due to extirpation of apex predators like the panther and red wolf, along with increases in mesomammalian predators (e.g., raccoon, opossum, foxes, bobcats), have led to concerns about increased predation on tortoise nests and juveniles. Therefore, we examined both short- and long-term effects of predation on gopher tortoise populations using a series of experimental approaches. These approaches included excluding mesomammalian predators from four large plots exclosures (40 ha plots) and reducing fire ant numbers is small enclosures (0.25 ha plots); treatment plots for each experiment were paired with untreated controls. In the experiments described above, we found that excluding mammalian predators and reducing red-imported fire ants resulted in increased gopher tortoise nest and hatchling survival (Pubs 3, 4). Nest location also was a factor in nest survival. We found that nests located at burrows had lower survival than nests located away from the burrow, suggesting that the burrow itself is a visual cue to predators like the nine-banded armadillo (Pub 5). This study highlights the need for habitat management with prescribed fire to maintain open sandy areas away from burrows as alternative nest sites for tortoises.
- We also found that red-imported fire ant presence significantly impacted nest hatching success and hatchling survival. Red-imported fire ants were attracted to tortoise nests shortly after egg deposition possibly due to olfactory cues rather than visual cues related to soil disturbance created by nesting activity. Red-imported fire ants were responsible for approximately 20% of the mortality of hatchling tortoises.
- Our study on the long term effects of mammalian predators on gopher tortoise populations within the large exclosure and control study plots is ongoing. We conduct surveys every 2-3 years (since 2003) and have captured and marked tortoises in study plots since 2018. Thus far, we’ve found that juvenile and sub-adult tortoise burrows have increased in exclosure plots suggesting that mesomammalian predators may have population-level impacts on gopher tortoises (Pub 3).
Red-imported fire ant effects on herpetofauna
The red imported fire ant, which was introduced to the southeastern U.S. from Argentina in the 1930s, is the dominant ant at Ichauway. This predatory ant has been linked to the decline of native vertebrates, including amphibians and reptiles, throughout the invaded range. As part of our research on predator ecology and management at Ichauway, we have examined the effects of red imported fire ants on southern toads, eastern fence lizards, and the gopher tortoise.
In a laboratory experiment, we found that the southern toad, a species that regularly eats ants, avoided red-imported fire ants. Avoidance of red-imported fire ants by southern toads likely decreases risks but may reduce foraging success since fire ants are dominant (Pub 7). Red imported fire ants negatively influenced recruitment of eastern fence lizards (Pub 8) but interestingly, this species was filmed feeding on fire ants (Pub 9). These findings supplement our research on the effects of fire ants on the gopher tortoise described above (Pubs 4, 6).
The longleaf pine ecosystem harbors a diverse snake community and snakes are important predators in this ecosystem. They are often perceived negatively because some species are predators of gamebirds. But snakes consume a wide array of prey including amphibians, other reptiles, mammals, and birds. Thus, individual snake species likely play important roles in longleaf pine food webs. Our research on snakes, using radio-telemetry to track movements, has addressed basic questions about habitat use, spatial ecology, and management for a suite of upland snake species including several species of conservation concern.
- Habitat use: Species endemic to uplands of the southeastern coastal plain (e.g., eastern diamondback rattlesnake, Florida pine snake, and eastern coachwhip) selected longleaf pine forests over oak-dominated forests at Ichauway, which highlights the importance of fire-maintained open-canopied forest habitats for these species (Pubs 10-12). Other, more generalist species (eastern kingsnakes and gray rat snakes) used a broader range of habitat types that included pine, hardwood, and edge habitats providing evidence for less specialized habitat requirements. At a local scale, gray rat snakes, are closely associated with individual oak trees (Pubs 13, 14).
In historically fire-maintained longleaf pine forests, like Ichauway, decayed stumps of trees killed by lightning, fire, or harvest, offer an important shelter and thermal refuge to eastern diamondbacks, eastern kingsnakes, and gray rat snakes (Pubs 13-16). Likewise, burrows created by longleaf pine- associated species including the gopher tortoise, oldfield mouse, and southeastern pocket gopher, provide important shelter for eastern diamondbacks, eastern coachwhips, and Florida pine snakes. (Pubs 11, 13, 15, 16).
- Spatial Ecology: A combination of large body size, foraging strategy, and habitat availability may help explain the variation in home-range size (the area used by an animal to conduct its daily activities) in snakes. The eastern coachwhip, the longest snake species at Ichauway had the largest average home range size (103 ha), whereas, shorter species had smaller average home range sizes; Florida pine snake (59 ha), eastern kingsnakes (50 ha), eastern diamondbacks (32 ha), and gray rat snakes (21 ha), (Pubs 10-12, 14, 17). The smallest snakes we’ve radio-tracked, newborn (neonate) timber rattlesnakes moved up to 24 m per day with little overlap in the home range. These movement patterns likely reduced competition between littermates (Pub 18).
- Management: Hardwood removal associated with longleaf pine restoration at Ichauway had limited suitable large oak trees that gray rat snakes used resulting in snakes having larger home range sizes than at other sites (Pub 14). Using our long term data on prescribed fire history, we found that three snake species of conservation concern, the eastern diamondback rattlesnake, Florida pine snake, and eastern coachwhip used sites burned frequently (at < 2.5-year intervals), whereas, two more widely distributed species, the eastern kingsnake and gray rat snake used sites across a broad range of frequencies (every 2 – 10 years).
The restoration of fire-suppressed habitats may require the use of fire surrogates, like hardwood reduction and herbicide application, together with the reintroduction of fire. In a study at Eglin Air Force base in the Florida Panhandle, we examined the effectiveness of all three approaches to restoration on wildlife species in fire-suppressed longleaf pine forests as compared to wildlife in reference forests. After more than a decade of prescribed burns alone, lizard and bird species occurrence was similar to reference sites (Pubs 19-21).
Seasonal Wetland Ecology
Isolated seasonal wetlands embedded in the longleaf pine forests are unique habitats for coastal plain fauna. Seasonal wetlands are abundant across the landscape, but they tend to be small and represent only about 2-3% of the total land area at a regional scale (Pubs 22-23). Despite their small size and seasonal pattern of filling and drying, these wetlands support high diversity, particularly among amphibians. For perspective, if seasonal wetlands were removed from Ichauway’s landscape, we would lose approximately 30% of our amphibian species. In addition, three amphibians dependent upon embedded seasonal wetlands (reticulated Flatwoods salamander, striped newt, and Florida gopher frog) are of conservation concern. Thus, research on patterns of diversity in seasonal wetlands at Ichauway has been a focus of our research program.
Diversity of isolated seasonal wetlands
We have found 25 amphibian species (7 salamanders and 18 frogs) in seasonal wetlands on Ichauway, including 14 wetlands used by the Florida gopher frog. The amphibian fauna differs slightly depending on the wetland vegetation type. Cypress-gum swamps, which are forested wetlands, support more salamander species than cypress savannas, which have a sparse canopy and dry frequently. More frog species occur in seasonal marshes, which are dominated by grasses and sedges (Pub 24). These studies emphasize the importance that different types of seasonal wetlands have in supporting biodiversity.
Although geographically isolated, many seasonal wetlands are intermittently “connected” via occasional surface water flows, which facilitate movements of materials and aquatic organisms, as well as by overland movements by organisms (Pubs 25-27).
American alligators and some aquatic turtles often move between seasonal wetlands and perennial streams in search of resources (water, food, and mates) (Pubs 28-29). Wading birds move seasonally between agricultural and natural isolated wetlands to maximize prey availability (Pub 30). These movements are reflected in patterns of genetic differentiation and diversity in mobile species like the southern leopard frog (Pub 31). Forest cover in the landscape surrounding wetlands influences amphibian abundance and diversity and likely facilitates movements (Pub 32).
Larval anurans (frogs) are important and abundant primary consumers (herbivores) in seasonal wetlands (Pubs 33-34), whereas larval caudates (salamanders) are among the top predators. As adults, these organisms often move between wetlands and between wetlands and surrounding uplands, potentially transporting nutrients across ecosystem boundaries. Understanding larval amphibian trophic roles, nutrient storage, and movements are important in determining their ecological significance and contributes to a more complete view of their functional role in seasonal wetlands.
Larval anurans are diverse and often the most abundant consumers in a wetland. We found that larvae of three common species, the southern cricket frog, barking tree frog, and southern leopard frog primarily function as herbivores/detritivores (Pub 34). Life-history traits, such as body size, developmental stage, and breeding season, of larval anurans, influenced the balance of key nutrients (carbon, nitrogen, and phosphorus) within their bodies and thus, their capacity for nutrient storage and transport (Pubs 35-36).
Rare, Threatened, and Endangered Species
Ichauway has populations of a number of amphibians and reptiles of conservation concern. Our uplands support one of the largest gopher tortoise populations in Georgia and several species of rare upland snakes. In recent years, we have documented populations of three rare amphibian species in seasonal wetlands, and Ichawaynochaway Creek and the Flint River host two rare turtle species. The management of Ichauway, which includes maintenance and restoration of longleaf pine and native ground cover with frequent prescribed fire and hardwood reduction offers a unique opportunity to study these species in high-quality habitats and to monitor their response to management.
Gopher tortoise populations are threatened across their range. Research that focuses on natural history and management aids in the recovery and conservation of this species. There is a long history of research on gopher tortoises including studies on tortoise behavior and movement patterns (Pubs 37-39). Recognizing this, we have established a long-term monitoring program, including the development of monitoring protocols for gopher tortoises.
- Monitoring: We developed standardized monitoring methods for gopher tortoises to enable stakeholders across the range of the species to obtain statistically valid and readily comparable population estimates. The standardized method includes systematic surveys using a distance sampling approach and burrow scoping to confirm tortoise presence (Pubs 40-45). The methods have been adopted by state and federal agencies across the range of the species.
- Management: Southeastern pine forests require active management including mechanical removal of hardwoods and frequent prescribed fire. Landowners also harvest trees for commercial value. Although these activities largely benefit tortoises, they require the use of heavy equipment, which raised concern about the impacts on gopher tortoises. We tested the effects of driving three common types of forestry equipment in proximity to unoccupied tortoise burrows and found that a buffer of 4m around a burrow was enough to minimize the risk of collapse from heavy equipment (Pub 46). We have also examined how animals respond to the prescribed fire by measuring the use of gopher tortoise burrows by vertebrates. We found that vertebrate use of burrows increased during and after a fire and the use of burrows was greater at burned than unburned sites (Pub 47).
- We are continuing to capitalize on early studies of gopher tortoises at Ichauway by re-trapping populations marked from 1995-2000. This work has allowed us to estimate the long term apparent survival of gopher tortoises, an important demographic parameter for determining population viability through time (Pub 48).
- Disease and tortoise behavior: Gopher tortoises at Ichauway have a long history of a high prevalence of antibodies for upper-respiratory-tract disease (URTD), but observations of tortoises with active symptoms of the disease are rare. To understand how URTD might potentially impact our population, we compared radio-telemetry data for tortoises tracked in 1997 to tracking data for the same population in 2011-2012. The home range size was stable across the two sampling periods. However, in a targeted study of tortoises exhibiting symptoms of active URTD, we found that these tortoises made atypically long movements. These movements may play an important role in the dispersal of the disease (Pubs 49-50).
Streams in the Lower Flint River Basin harbor a high diversity of freshwater turtles. On Ichawaynochaway Creek, we have documented nine species of turtles that include two species of conservation concern, the alligator snapping turtle and Barbour’s map turtle. Our studies have focused on the status of these species and the potential effects of land-use change on instream habitat.
We found that turtle diversity in streams is positively related to the percentage of riparian forest (Pub 51) and that large wood debris within streams provides an important refuge for female Barbour’s map turtles (Pub 52). Our 2015 surveys of the Flint River population of Alligator snapping turtles did not show an increase despite 22 years of protection from legal harvest. This finding suggests that life-history characteristics, including delayed maturity and low reproductive output, and possible mortality of adult turtles as unintentional bycatch, are limiting the recovery of this population (Pub 53).
Education and Outreach Activities
Gopher tortoise workshops
- Workshop on the Ecology, Status, and Management of the Gopher Tortoise: From 16-17 January 2003, 30 invitees from 6 states gathered at the Jones Center for a workshop to exchange data on tortoise biology and status, and to identify research needs that might lead to more effective range-wide conservation (Pub 54).
- Gopher Tortoise Survey Training Workshops: Since 2012, we have led 11 gopher tortoise survey training workshops that included hands-on classroom and field activities focused on designing, implementing, and analyzing survey data to estimate tortoise abundance (Pub 55).
- Gopher Tortoise Population Viability Workshops: The first of a series of workshops was held in 2013, to derive a working definition of what represents a viable population and minimum reserve size for the gopher tortoise (Pub 56). At the second workshop, in 2014, the objectives were to reach a consensus on the number, size, and distribution of viable gopher tortoise populations to ensure the long-term viability of the species (Pub 57).
We host several university classes each year, including the UGA herp class.
We have co-taught week-long field university field courses with undergraduate and graduate students from the University of Georgia, University of Alabama, Auburn University, University of Florida, University of Central Florida:
- Coastal Plain Ecosystems: Ecology and Management
- Aquatic ecosystem of the Southeastern Coastal Plain
Active in the Gopher Tortoise Council
Jen Howze currently serves on the board of the Gopher Tortoise Council.