Craig Guyer’s research while affiliated with Auburn University and other places

In the North American longleaf pine (Pinus palustris) ecosystem, the Gopher Tortoise (Gopherus polyphemus) is a keystone species that has declined significantly over the last century. Habitat degradation and fragmentation may have caused G. polyphemus to become separated into small, isolated local populations that suffer from decreased genetic diversity or inbreeding depression. Here we use genome-scale methods to sequence thousands of loci for 336 G. polyphemus individuals from 11 sites across southern Alabama to estimate population genetic structure and levels of genetic diversity. We found a pattern of isolation by distance among samples, where geographic distance predicted genetic difference. Principal components and structure analyses supported the existence of three weak genetic populations comprising individuals from (1) Fred T. Stimpson State Game Sanctuary and Perdido Wildlife Management Area, (2) Conecuh National Forest and Solon Dixon Forestry Education Center, and (3) Geneva State Forest Wildlife Management Area. We did not observe strong variation in genetic diversity or effective population size metrics among sampling locations or genetic populations identified by population structure analyses. Our results suggest that G. polyphemus historically operated on larger geographic scales than those considered by contemporary mark-recapture studies. Absence of variation in population genetic metrics suggests that either effects of fragmentation have not manifested themselves, or that the effects are similar across all locations. Given the common use of translocations in Gopher Tortoise management, we provide a framework for tortoise translocations based on our genomic data.

Reintroduction of species at sites where populations have been extirpated has become a common technique in wildlife conservation. To track progress towards reintroduction success, effective postrelease monitoring is needed to document vital rates of individuals and the corresponding impact on population trajectories. We assessed growth and body size in Eastern Indigo Snakes (Drymarchon couperi) using a data set from multiple projects across the species' distribution, including free-ranging wild snakes, snakes reared in captive-breeding programs, and snakes released at two reintroduction sites. We used these data to fit a von Bertalanffy growth model in a Bayesian framework to quantify differences in growth among three broad categories of snakes (wild, captive, and reintroduced), while accounting for measurement error across various projects. We also compared changes in body mass of captive-born individuals from four captive rearing facilities. Asymptotic snout–vent length across all groups was 185 cm (95% credible interval = 177–194 cm) for males and 157 cm (95% credible interval = 153–161 cm) for females. Reintroduced snakes had a higher growth coefficient than either captive or wild snakes (e.g., captive females = 1.20 [1.06–1.35] d–1; wild females = 1.22 [0.95–1.49] d–1; reintroduced females = 1.62 [1.21–2.05] d–1), indicating that current captive-breeding and rearing efforts for indigo snakes produce similar or faster growth trends compared to wild populations. Furthermore, daily changes in juvenile body weight relative to body size were similar in three of the four captive rearing facilities (mean for females at Orianne Center for Indigo Conservation = 0.57 [0.48–0.65]; Zoo Atlanta = 0.55 [0.37–0.72]; Welaka National Fish Hatchery = 0.55, [0.36–0.73]; Auburn University = 0.39 [0.21–0.58]). Long-term project success for indigo snake reintroductions will depend on continuing to implement best practices in an adaptive management framework.

Macrochelys temminckii (Alligator Snapping Turtle) has experienced historical harvesting pressures that impact a number of current populations. Filling distribution gaps and obtaining demographic data can better inform conservation and management. We summarized multi-year samples targeting the Alligator Snapping Turtle in large river systems and major tributaries of Alabama. Although catch per unit effort was lower than observed in other states, we filled distribution gaps in several river systems. Though studies from other states documented effects of historical harvesting pressure on Alligator Snapping Turtle populations, mean adult mass of both sexes, mean carapace length, and capture ratio of adults to immatures suggested reduced pressures in Alabama and possible population stability. Nevertheless, smaller tributaries and creeks need to be surveyed for previously undetected populations with mark–recapture and movement studies.

We performed systematic surveys for members of the Eurycea quadridigitata (Dwarf Salamander) complex in Georgia to determine the distribution of member species. Over 409 person-hours of search effort, we sampled 211 locations in 38 counties, detecting 108 individuals, including many that bridge substantial distribution gaps. Molecular data document Georgia specimens belong to 2 species, E. hillisi and E. quadridigitata. No specimens attributable to E. chamberlaini were found in Georgia, indicating this species has a distribution restricted to South and North Carolina. We used color patterns and measures of body size and shape of specimens identified by molecular methods to separate 4 species of 4-toed Eurycea from the Coastal Plain of Alabama, Florida, Georgia, South Carolina, and North Carolina. Large body size and the presence of melanophores across the chin and surrounding the cloaca separated E. quadridigitata from all others. Additionally, E. sphagnicola and E. quadridigitata possessed dark sides to the body and tail, with these features being disrupted by irregular white stripes or spots. In contrast, E. chamberlaini and E. hillisi possessed light sides to the body and tail that lacked irregular white stripes. Small body size distinguished E. sphagnicola from E. quadridigitata, but no feature distinguished E. chamberlaini from E. hillisi.

In seasonal wet Neotropical forests, many studies have suggested that species-rich terrestrial frog assemblages are regulated bottom-up by the abundance of leaf litter. However, terrestrial frogs are prey to a diverse community of predators, and no studies have tested for top-down effects of predators on this or other anuran assemblages. Here, we used an extensive field dataset to model the relative contribution of food resources, microhabitat resources and predators towards the occupancy and detection of two frog species ( Craugastor bransfordii and Oophaga pumilio ) at La Selva, Costa Rica. Frog occupancy was most strongly influenced by predatory spiders and secondarily influenced by the abundance of leaf litter. Predators exerted stronger effects on frogs than food resources, and frogs avoided predators more as leaf litter decreased. Detection probability was elevated when predators were present. We found support for bottom-up effects of leaf litter on the terrestrial frog assemblage, but top-down effects by predators exerted stronger effects on frog occupancy and detection. Because predator avoidance varied along a resource gradient, predator and resource effects appear to be dependent, supporting interactions between top-down and bottom-up mechanisms. Climate-driven decreases in leaf litter may drive decreased availability of frog refugia and increased interactions between frogs and predators.

The Argentine Black and White Tegu (Salvator merianae, formerly Tupinambis merianae) is a large lizard from South America. Now established and invasive in southern Florida, and it poses threats to populations of many native species. Models suggest much of the southern United States may contain suitable temperature regimes for this species, yet there is considerable uncertainty regarding either the potential for range expansion northward out of tropical and subtropical zones or the potential for the species establishing elsewhere following additional independent introductions. We evaluated survival, body temperature, duration and timing of winter dormancy, and health of wild-caught tegus from southern Florida held in semi-natural enclosures for over a year in Auburn, Alabama (> 900 km northwest of capture location). Nine of twelve lizards emerged from winter dormancy and seven survived the greater-than-one-year duration of the study. Average length of dormancy (176 d) was greater than that reported in the native range or for invasive populations in southern Florida and females remained dormant longer than males. Tegus grew rapidly throughout the study and the presence of sperm in the testes of males and previtellogenic or early vitellogenic follicles in female ovaries at the end of our study suggest the animals would have been capable of reproduction the following spring. The survival and overall health of the majority of adult tegus in our study suggests weather and climate patterns are unlikely to prevent survival following introduction in many areas of the United States far from their current invasive range.

Population viability analyses are useful tools to predict abundance and extinction risk for imperiled species. In southeastern North America, the federally threatened gopher tortoise (Gopherus polyphemus) is a keystone species in the diverse and imperiled longleaf pine (Pinus palustris) ecosystem, and researchers have suggested that tortoise populations are declining and characterized by high extinction risk. We report results from a 30‐year demographic study of gopher tortoises in southern Alabama (1991–2020), where 3 populations have been stable and 3 others have declined. To better understand the demographic vital rates associated with stable and declining tortoise populations, we used a multi‐state hierarchical mark‐recapture model to estimate sex‐ and stage‐specific patterns of demographic vital rates at each population. We then built a predictive population model to project population dynamics and evaluate extinction risk in a population viability context. Population structure did not change significantly in stable populations, but juveniles became less abundant in declining populations over 30 years. Apparent survival varied by age, sex, and site; adults had higher survival than juveniles, but female survival was substantially lower in declining populations than in stable ones. Using simulations, we predicted that stable populations with high female survival would persist over the next 100 years but sites with lower female survival would decline, become male‐biased, and be at high risk of extirpation. Stable populations were most sensitive to changes in apparent survival of adult females. Because local populations varied greatly in vital rates, our analysis improves upon previous demographic models for northern populations of gopher tortoises by accounting for population‐level variation in demographic patterns and, counter to previous model predictions, suggests that small tortoise populations can persist when habitat is managed effectively. © 2021 The Wildlife Society. Small gopher tortoise populations (10–50 individuals) may be stable and persist with low extinction risk if adult female survival is sufficiently high (≥0.95).