Herpetology II

Contributed Paper
ROOM: HCCC, Room 16

1:10PM Using Predictive Models to Support Endangered Species Listing Decisions in the Species Status Assessment of Sonoran Desert Tortoise.
Conor P. McGowan; Nathan Allan; Jeff Servoss; Shaula Hedwall; Brian Wolldridge
Assessment of a species’ status is a key part of management decision making for endangered and threatened species under the U.S. Endangered Species Act. Predicting the future state of the species is an essential part of species status assessment, and projection models can play an important role in developing predictions. We built a stochastic simulation model that incorporated parametric and environmental uncertainty to predict the probable future status of the Sonoran desert tortoise (Gopherus morafkai) in the southwestern United States and North Central Mexico. Sonoran desert tortoise was a Candidate species for listing under the Endangered Species Act, and decision makers wanted to use model predictions in their decision making process. The model accounted for future habitat loss and possible effects of climate change induced droughts to predict future population growth rates, abundances, and quasi-extinction probabilities. Our model predicts that the population will likely decline over the next few decades, but there is very low probability of quasi-extinction less than 75 years into the future. Increases in drought frequency and intensity may increase extinction risk for the species. Our model helped decision makers predict and characterize uncertainty about the future status of the species in their listing decision. We incorporated complex ecological processes (e.g., climate change effects on tortoises) in transparent and explicit ways tailored to support decision making processes related to endangered species.
1:30PM Habitat Characteristics of Military Test Ranges and Forested Sandhills Used By Gopher Tortoises on Eglin Air Force Base, Florida
William Moore
The gopher tortoise (Gopherus polyphemus) is a species of conservation concern due to declines caused primarily by habitat loss. Eglin Air Force Base (Eglin) contains some of the largest remaining tracts of potential habitat for the species. However, fire suppression and harvest for food in past decades have reduced the tortoise population on Eglin. Currently, tortoises are relegated to treeless military test ranges or occur in isolated clusters within forested sandhills, typically at low densities. Burrow densities, particularly within juvenile size classes that would indicate recruitment, vary considerably among test ranges, presumably from differences in management strategies and mission use across sites. To mitigate future conflicts between conservation goals and military training objectives, it is important to assess the value of test ranges to gopher tortoises and to better understand why tortoises appear to occur at higher densities on test ranges versus adjacent forested sandhills. Here, we conducted vegetation surveys with an emphasis on herbaceous ground cover composition. Preliminary results suggest that test ranges have significantly higher mean percent forage (herbaceous) cover (graminoids: 37.5±3.6 vs. 16.9±4.0, forbs: 28.5±4.8 vs. 24.3±8.3), fewer shrubs (13.7±2.4 vs. 30.5±6.0), and lack canopy cover compared to forested sandhills. Plant species richness, composition, and amount of disturbance-prone species varied considerably among test ranges and differences in major plant cover classes did not appear to correspond to differences in burrow densities among sites. Additionally, nesting season mowing events impacted aprons, likely causing nest failure, and collapsed burrows at two sites. While it appears test ranges have the potential to serve as high-quality tortoise habitat, timing and frequency of mechanical treatments likely influences recruitment. Further, increased fire return intervals and other management techniques may be necessary to improve degraded sandhill sites and could facilitate connectivity between high-quality forested patches and test ranges.
1:50PM Influence of Plasticity and Range Position on Increased Maintenance Energy Costs of the Red-Backed Salamanders during the Summer
David J. Munoz; David A.W. Miller; Ruudolf Schilder; Evan H. Campbell Grant
Maintenance energy costs are a significant portion of ectotherm energy budgets, and they scale exponentially with temperature. In temperate regions summer represents the period of highest energy costs. For wide ranging species, southerly populations must deal with longer and warmer summers. Climate change will intensify summer heat and length, increasing energy costs most dramatically at lower latitudes. Some organisms may be able to adapt, but others may buffer themselves from excess maintenance costs through physiological plasticity (i.e. modification of their metabolic rate). Plethodontid salamanders are particularly vulnerable because they prefer cool conditions and live a low-energy lifestyle. We investigate Plethodon cinereus, a wide-ranging terrestrial salamander to determine whether species in this taxon are able to 1) modify metabolic rates based on thermal cues, 2) adjust rates for future climate conditions, and 3) show consistent responses across populations. We collected 36 individuals from each of four populations: Virginia, Pennsylvania, New York, Massachusetts. We estimated thermal relationships in metabolic rate across three acclimation regimes (home spring temperature, home summer temperature, and home summer temperatures +4C—from climate models). We conducted a total of 1724 metabolic trials and found plasticity in PA and VA populations between spring and summer temperatures. This reduced their maintenance costs by 48% and by 27%, respectively. New York and Massachusetts showed no plasticity. Our findings show southern populations can reduce their summer energy costs; whereas northern populations may not experience warm enough temperatures to require metabolic plasticity. None of the populations showed differences between summer and +4C warming regimes, meaning all populations are likely at their limit of possible acclimation. Future warming will increase energy costs for all populations, but we predict southern populations will experience higher mortality, less individual growth, and lower recruitment unless other mechanisms can their increase energy acquisition or alter energy allocation patterns.
2:10PM Withering Waters & Teetering Temperatures: How One Frog Copes with Pool Permanency
Cassandra M. Thompson; Viorel D. Popescu
Environmental variation during development can have profound, variable effects on an organism’s phenotype, physiological attributes, and overall fitness. With increasing environmental temperatures and higher frequency of extreme events, ectotherms across the globe are expected to experience thermal ranges and extreme heat events beyond their physiological capacity. Anurans have a dual life cycle, raising the question of whether detrimental environmental conditions experienced in the aquatic (larval) stage are carried over in the terrestrial (juvenile and adult) stage, and whether the negative impacts on growth and survival in the larval stage are exacerbated by changes in temperature and moisture availability in the terrestrial realm. Notably, while many studies have focused on the effects of pool permanency on developmental rates and survival of larval amphibians, few have considered carryover effects into the metamorph life stage. We evaluated the impact of hydro-period length on wood frogs (Lithobates sylvaticus), a model forest specialist. Our specific objectives were to (1) evaluate the impacts of drying conditions on larval development and survival, (2) evaluate carryover effects from the aquatic stage on locomotor performance (endurance) of metamorphs, and (3) evaluate carryover effects into the terrestrial habitat on growth and survival. While we found significant differences in larval survival, size at metamorphosis, and locomotor performance of metamporphs between hydro-period treatments, we found no significant differences in juvenile terrestrial growth and survival. Since juvenile anurans are the population-regulating stage for pond-breeding amphibians, understanding how factors experienced during the larval stage affect the fitness of juveniles and adults through an entire annual cycle is informative for population growth models and viability and better understanding how conditions experienced during the aquatic stage affect their physiological capacity to respond to changing environments.


Contributed Paper
Location: Huntington Convention Center of Cleveland Date: October 11, 2018 Time: 12:50 pm - 2:30 pm