Herpetofauna I

Contributed Oral Presentations

SESSION NUMBER: 14

Contributed paper sessions will be available on-demand for the duration of the conference, then again at the conclusion of the conference.

 

Accounting for Multiple Uncertainties to Evaluate Population Viability of the Alligator Snapping Turtle for the Species Status Assessment
Abby J. Lawson; Stephanie M. DeMay; Erin Rivenbark; Karen Soileau; Kaye London; J. Hardin Waddle; Lisa Yarborough; Conor P. McGowan
Turtles are among the most threatened of the major vertebrate groups world-wide. The alligator snapping turtle (Macrochelys temminckii; AST hereafter) is the largest freshwater turtle in North America and primarily inhabits riverine habitats in the southeast and lower midwestern states. Evaluating AST population trends is challenging due to their cryptic nature, though it is well-established that populations are exposed to multiple, overlapping threats throughout their range including fishing bycatch, hook ingestion, poaching, and nest depredation by subsidized predators. We evaluated AST population viability for the AST Species Status Assessment to inform the U.S. Endangered Species Act listing decision. We constructed a baseline matrix population model using demographic parameters from peer-reviewed literature to reflect an idealized population, exposed to minimal threats. We used expert-elicitation to quantify threat spatial extents and threat-specific reductions to survival within eight geographic units. To account for uncertainty of the expert-elicited quantities, we created six scenarios in which the threat-specific survival reductions were unaltered or changed ± 25%, and the spatial extents unaltered or reduced 25% to reflect the effect of potential conservation actions. We performed 500 stochastic replicates for each geographic unit and scenario combination to simulate AST population dynamics over 50 years. Expert-elicited data indicated that poaching and hook ingestion exhibited the largest percent reduction to adult survival (19% and 8%, respectively). In general, AST populations showed low resiliency, as the probability of population extirpation averaged 0.25 ± 0.22 SD across all geographic units and scenarios. The presence of conservation actions had a positive effect, increasing the time to extirpation by an average of 2.97 ± 1.98 SD years, compared to conservation-absent scenarios. Our study illustrates how expert-elicited data can be used to account for uncertainties in assessing population viability for cryptic and data deficient species to inform conservation decisions.
Individual Growth Rates and Bycatch As Limiting Factors in a Freshwater Turtle Reintroduction
Ethan Kessler; Michael Dreslik
Reintroduction projects aim to produce self-sustaining populations and structured population models (SPMs) are commonly used to predict success. Integral projection models (IPMs) are a flexible SPM using continuous measures within fitted models to better match demography. We used IPMs to predict the outcome of an Alligator Snapping Turtle (Macrochelys temminckii) reintroduction in Illinois. The population displays reduced growth rates and has lost sexually mature adults to bycatch. I modeled survival and individual growth under scenarios with observed and ideal rates to estimate population growth and identify potential sources of unstable demography. Modeled individual growth rates in this population predicted size at sexual maturity occurs at 25.9 years old, nearly twice the age of sexual maturity in natural populations. Interactive effects of size and season best explained survival with younger turtles showing greater vulnerability to overwinter mortality. IPM scenarios show a declining population (λ=0.95) and, while removing bycatch improved population growth rates, only increased individual growth resulted in a stable population. Elasticities showed a reliance upon individual growth and survival, especially in adults, for population growth. Our results demonstrate unstable demography in the reintroduced population. However, with more natural individual growth and survival rates, the population could achieve stability. With no feasible way to improve individual growth rates, reintroduction failure is a likely outcome and addressing bycatch should be a priority to maximize the chance of a favorable result.
Climate Effects on Nesting Phenology in Nebraska Turtles
Daniel Greene; Ashley Hedrick; Erin Lewis; Andrew Hood; John Iverson
A frequent response of organisms to climate change is to alter the timing of reproduction. In particular, advancement of reproductive timing has been a common response to warming temperatures in temperate regions in a variety of organisms. At our study site in Nebraska, the timing of nesting of the Common Snapping Turtle (Chelydra serpentina) was negatively correlated with mean maximum temperatures during the preceding December and mean minimum temperatures in May. For the Painted Turtle (Chrysemys picta), the timing of nesting was positively correlated with mean minimum temperatures in September and negatively correlated with mean maximum temperatures in May. Increased temperatures during late winter and spring likely permit earlier emergence from hibernation, increased metabolic rates and feeding opportunities, and accelerated vitellogenesis, ovulation, and egg shelling, all of which would drive earlier nesting. However, nest timing in Chelydra was also inversely related to December temperatures, whereas in Chrysemys early fall temperatures were positively correlated with nesting dates during the following summer. For both species, nest deposition was highly correlated with body size, where larger females nested earlier. For example, the predicted range for Chrysemys nest deposition ranged from June 12 to June 3 for females between 150 to 204mm, respectively. Although average annual environmental temperatures have increased over the last four decades at our study site, spring temperatures have not, and hence nesting phenology has not advanced at our site for Chelydra, and likely not for Chrysemys. Although Chrysemys experienced an approximate 6 day delay in nest deposition, this response is likely due to recruitment of smaller females into the population from nest protection and predator control that occurred in the late 1990s and early 2000s. Should climate change eventually result in an increase in spring daytime temperatures, nesting phenology would presumably respond accordingly, conditional on body size of nesting females.
Climate Variability Influences Aspects of Fecundity But Not Survival in a Long-Lived Species, the Gopher Tortoise
Elizabeth A. Hunter; Kevin T. Shoemaker; David C. Rostal
Long-term capture-mark-recapture (CMR) datasets with linked fecundity data are critical for estimating how environmental variability affects population trends in long-lived species, including gopher tortoises (Gopherus polyphemus), because fecundity is more likely to be sensitive to climatic variability than survival in long-lived species. Our objective was to estimate effects of climatic variation on gopher tortoise population vital rates using a 25-year CMR dataset collected at Fort Stewart Army Reserve in Georgia. Adult tortoises were captured primarily in the summer via bucket trapping or hand capture and marked using passive integrated transponder (PIT) tags and notching. All females were ultrasounded to detect the presence of shelled eggs, and subsequently x-rayed to measure clutch size. We used a Bayesian hierarchical CMR model to estimate adult survival/emigration, recruitment/immigration into the adult population, and adult population size, and a zero-inflated Poisson model to estimate components of fecundity (probability of reproducing and clutch size). We searched for effects of climate (maximum temperature, precipitation, and monthly temperature range) on population vital rates using a moving window analysis in the 24-month period prior to the summer census date. Adult population vital rates were all affected by management (prescribed burning); however, they were not sensitive to any climate variables, indicating that adult survival is invariant to climatic fluctuations. Clutch size was not affected by climate and was primarily a function of female body size. The probability of reproducing was affected by precipitation in the preceding 18 months, with very low or very high precipitation reducing reproduction probability, and was also negatively affected by temperature variability in the preceding summer, which is when vitellogenesis for egg production and mating occur. Sensitivity of reproduction probability to climate may increase population vulnerability to climate change if there is no compensatory response by other vital rates such as hatching success or juvenile survival.

 

Virtual
Location: Virtual Date: Time: -