Software-Angebote gopher Druck- und Scan-Dienste Kurstermine Sommersemester 1993

Gopher tortoises are ecosystem engineers whose burrows provide habitat to >350 species. Prescribed fire is used to manage tortoise habitat, but fire timing is mostly restricted to the vegetative dormant season. Restricted fire timing in combination with white-tailed deer competition may negatively affect tortoises. To address these concerns, we quantified these species’ dietary overlap and conducted a field experiment to examine impacts of fire phenology on plants and animals. Although tortoises and deer consumed ~75% of the same plants, their diets were statistically dissimilar. Fire altered plant community composition and increased foliar crude protein and phosphorus while decreasing calcium. Deer detections were unaffected, but tortoises were detected more in fire treatment plots. We simultaneously monitored burrow and surface temperatures and found burrows provide thermal refuge. Our data suggests that fire timing affects plants in ways that can affect gopher tortoises, and burrows may mitigate some negative impacts of climate change.

Nesting and early life is a period of high mortality for many turtle species, so understanding how turtles select nest sites, and how those nest sites impact hatching success, may be important for successful species conservation. In this research, my objective was to 1) understand how the environment around potential nest sites (canopy, understory, and soil) influences gopher tortoise nest-site selection at burrows and 2) how that nest environment both directly (nest microclimate: temperature and moisture) and indirectly (nest characteristics: nest depth, distance from burrow, canopy and understory cover, percent clay in soil, and lay date) affects hatching success in naturally incubated tortoise nests. In the summers of 2022 and 2023, I conducted repeated searches at burrows to locate nests at the Jones Center at Ichauway and the Greenwood Ecological Reserve in southwestern Georgia. I collected soil samples, measured canopy and ground cover at gopher tortoise nest locations (n=132) and an equal number of comparison non-nest burrows. At nest sites, I also monitored temperature and moisture throughout incubation. To evaluate nest-site selection, I compared burrows with and without nests using multiple logistic regression to create a suite of five biologically relevant candidate models and compared models with Akaike's Information Criterion adjusted for small sample sizes. The top three models identified canopy cover and understory vegetation cover as the only significant predictors of nest presence at burrows, with tortoises in the sites nesting at burrows with lower understory and canopy cover. Furthermore, there was an interaction between the understory vegetation and canopy cover effects, where the effect of understory cover decreased as canopy cover increased. This suggests that the vegetation effect may be primarily driven by an avoidance of shade, whereby nests laid in burrows with high canopy cover were so shaded that understory vegetation had a weaker influence on nest-site selection. When tortoises nested in burrows with lower canopy cover, which was far more common than high canopy cover at our sites, they also avoided understory vegetation so that nest sites were least shaded. These results suggest that maintaining habitats with very open overstories may be most important for allowing gopher tortoises access to preferred nest sites. To quantify the direct and indirect effects of nest environment on hatching success, I built a structural equation model (SEM) in a Bayesian framework in which hatching success was affected by nest temperature and moisture, which were themselves affected by nest site characteristics. I found that nest microclimate could be predicted moderately well from characteristics of the nest environment (R2=0.25-0.49), with lay date influencing both temperature and moisture, vegetation affecting temperature, nest position influencing moisture and temperature variability, and percent clay in soil influencing moisture. Hatching success was highest at lower mean temperatures and moistures and at intermediate levels of temperature and moisture variability, but the ability of this model to predict hatching success was low (R2=0.10). I observed very high hatching success (87.5%) and, thus, eggs were generally receiving the conditions they needed to successfully develop and there was not much variation in hatching success to explain. This framework may be useful for investigating environmental causes of lower hatching success at less robust tortoise populations that may be experiencing low rates of natural hatching success. / Master of Science / Many turtle species experience high rates of mortality in early life, so understanding how turtles select areas to nest, and how those places impact hatching success, may be important for successful species conservation. In this research, my objective was to 1) understand how the environment around potential nest locations (vegetation and soil) influences where gopher tortoise place nests at burrows and 2) how the conditions of that nest location both directly and indirectly affect hatching success in natural gopher tortoise (Gopherus polyphemus) nests. In the summers of 2022 and 2023, I conducted repeated searches at burrows to locate nests at the Jones Center at Ichauway and the Greenwood Ecological Reserve in southwestern Georgia. I collected soil samples, measured canopy and vegetative ground cover at gopher tortoise nest locations and an equal number of burrows without nests. At nest sites, I also monitored temperature and moisture throughout incubation. To evaluate how tortoises chose nest locations, I created models to compare tortoise burrows with nests to burrows that were available for nesting, but where no nest was placed. The top three models identified canopy cover and understory vegetation cover as the only significant predictors of nest presence at burrows, with tortoises in my sites nesting at burrows with lower understory and canopy cover. Furthermore, there was an interaction between the understory vegetation and canopy cover effects, where the effect of understory cover decreased as canopy cover increased. This suggests that the vegetation effect may be primarily driven by an avoidance of shade, whereby nests laid in burrows with high canopy cover were so shaded that understory vegetation had a weaker influence on nest-site selection. When tortoises nested in burrows with lower canopy cover, which was far more common than high canopy cover at my sites, they also avoided understory vegetation so that nest sites were least shaded. These results suggest that maintaining habitats with open overstories may be most important for allowing gopher tortoises access to preferred nest sites. To quantify the direct and indirect effects of nest environment on hatching success, I built a structural equation model (SEM) in which hatching success was predicted by nest temperature and moisture, which were themselves predicted by nest-site characteristics. This allowed me to evaluate both the direct effects of nest temperature and soil and the indirect pathways by which nest environment may be influencing hatching success. I found that nest temperature and moisture could be predicted moderately well from characteristics of the nest environment (R2=0.25-0.49), with the date the nest was laid influencing both temperature and moisture, vegetation around the nest affecting temperature, nest position influencing moisture and temperature variability, and percent clay in soil influencing moisture. Hatching success was highest at lower mean temperatures and moistures and at intermediate levels of temperature and moisture variability, but the ability of this model to predict hatching success was low (R2=0.10). I observed very high hatching success (87.5%) and, thus, eggs were generally receiving the conditions they needed to successfully develop and there was not much variation in hatching success to explain. This framework may be useful for investigating environmental causes of lower hatching success at less robust tortoise populations that may be experiencing low rates of natural hatching success.

Understanding worldwide declines in reptiles due to factors such as habitat loss and emerging infectious disease has become an increasingly important focus in conservation biology. Here, I use novel approaches from the field of landscape genetics to combine spatial genetic data with landscape data at both regional and local spatial scales to explore natural and anthropogenic landscape features that shape population structure and gene flow in a federally threatened reptile, Gopherus polyphemus. I also utilize approaches from the field of spatial epidemiology to examine the extent to which environmental variables can be used to predict the seroprevalence of an associated pathogen Mycoplasma agassizzi in gopher tortoise populations. Using mitochondrial data, I find evidence of a historical barrier to gene flow that appears to coincide with the Apalachicola River. I also discover low genetic diversity and evidence of population bottlenecks in the western portion of the range. My evaluation at the regional scale shows that dispersal is limited by geographic distance, areas of low elevation and major roads ways. A finescale study reveals no evidence of spatial genetic structure within a 14 x 35 km area. However, soil type is significantly correlated with pairwise genetic distances between individuals, suggesting that this variable influences fine-scale population structure in the gopher tortoise. In addition to soil, high density canopy cover is an important factor impeding gene flow at the local level for females, while land cover type explains some of the genetic variance between males. Finally, temperature and precipitation appear to be important predictors of the seroprevalence of the pathogen Mycoplasma agassizii in gopher tortoises. The probability of an individual testing seropositive for exposure to this disease increased with high temperature and low precipitation values. The methods presented in this dissertation evaluate novel approaches for assessing the influence of environmental variables on population structure, dispersal and disease occurrence and could be applied in future studies of other threatened and endangered taxa.

Gopherus polyphemus populations are diminishing throughout their range due to urbanization, fragmentation, and poor management of habitats. Increased population densities, poor habitat quality, and lack of fire may influence disease transmission. Parasite roles within wild tortoise populations are largely unknown, despite evidence these pathogens may pose health risks. This study provides a baseline of gopher tortoise endoparasites across South Florida and reports on how varying environmental and tortoise characteristics may affect endoparasite species prevalence, approximate loads, and overall distributions. Tortoise fecal samples were taken from five differing SF habitats. Seven species of intestinal parasites were discovered from 123 tortoises. Identified parasites include endo-helminths such as cyathostomes, pinworms, ascarids, flukes, and protozoans including Eimeria, Cryptosporidium, and Amoeba species. Significant differences in parasite prevalence and loads were seen between sampling years, seasons, size classes, and sites, however, overall parasite distributions suggest parasitism remains relatively ubiquitous throughout most host and site characteristics. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2017. / FAU Electronic Theses and Dissertations Collection

Many Gopher Tortoise populations are in steep decline throughout Florida, and various measures have been attempted to curb the trend. One such measure is to relocate tortoises to protected recipient sites on private lands. The majority of private lands in Florida are used for cattle, however, production and the effect of cattle production on tortoises is not known. Here, I tested six parameters of tortoise behavior by monitoring 1403 gopher tortoises released at the Barthle Brothers Ranch, Pasco County Florida, between August 2009 and December 2012. The parameters tested were (1) burrow density, (2) burrow spacing, (3) burrow relocation, (4) body condition, (5) individual growth rate, and (6) recruitment (addition of young to the population). I used telemetry techniques to observe movement and burrow placement as it related to cattle activity and burrow impacts, and collected morphological data to determine changes in body condition and growth. I used burrow surveys and analyzed movement patterns to interpret the propensity for tortoises to place burrows where cattle may or may not congregate. Lastly, I investigated recruitment of juveniles into the population and followed the mortality of resident and relocated tortoises in all treatment plots. I found that burrow density, distance moved when relocating to new burrows, and avoidance of cattle were not distinguishably different within or between the plots. Burrow relocation, however, was more frequent outside the exclosures. The change in body condition did not differ between males and female or resident and relocated individuals. Females within the exclosure did not grow at a rate different than those outside the exclosure although translocated females grew faster than resident females. Densities of non-adult burrows inside the exclosures were not different then densities outside the exclosure. Eleven percent of tortoises relocated to the ranch died during the project. Although we have no evidence that cattle and tortoise cannot successfully coexist, a number of circumstances prevented rigorous testing of our hypotheses, predominately the failure of the silt fence used to enclose the treatment plots. Using a trespass-proof perimeter fence would allow a better assessment of the actual interaction between the cattle and tortoises and may shed new light on the lack of recruitment and the decline of juvenile tortoises relocated to the ranch. Without recruitment of individuals back into a population, or the persistent of reproducing adults within the population, any efforts to curb the downward trend in gopher tortoise numbers by relocating tortoises to actively grazed pasture is futile.

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The Mississippi gopher frog (MGF, Lithobates sevosa) is a critically endangered amphibian which requires the use of assisted reproductive technologies (ART) to successfully reproduce in captivity. Several challenges to successfully breeding MGFs were investigated to improve reproduction in this species. Accurate identification of biological sex is a necessary first step to reproducing species, thus several non-invasive techniques for sex identification were compared in the weakly dimorphic MGF. Reliably obtaining eggs from female MGFs has also proved difficult, therefore, four exogenous hormone therapies were compared for their success to induce ovulation. Ultrasound imaging was used alongside hormone treatments to improve understanding of ovarian response to hormone treatment. Lastly, short-term cold storage of spermic urine was studied to determine the feasibility of this technique for MGF gamete storage. Findings from these research projects are important for the successful conservation of the MGF by aiding in the production offspring for future reintroduction programs.

Recent studies have shown environmental factors influence life history traits in fishes. Understanding intraspecific variability of life history characteristics and condition is necessary to determine local fisheries management strategies. Gopher rockfish, Sebastes carnatus, comprise 50% of the estimated shallow nearshore recreational rockfish catch in California, yet insufficient local data exist regarding life history traits and condition of this species. Our study locally defines growth parameters (maximum size and age), size (age) at reproductive maturity, and condition (hepatosomatic indices) for gopher rockfish in south central California. The growth parameter values of gopher rockfish from our study are similar to previously published research. However, our data also indicate that the current local gopher rockfish stock in south central California reaches reproductive maturity at a larger size and an older age when compared to gopher rockfish sampled throughout central California (primarily in Monterey) between 1977-1982. Furthermore, we examined spatial and temporal differences in life history information, within and outside of two south central California Marine Protected Areas (MPAs) established in 2007, between two time periods. Our data show that the size and longevity of fish has increased after the establishment of MPAs.

Gopherus polyphemus, commonly known as the Gopher Tortoise, is a dryland reptile native to the southeastern United States. It is commonly a resident of longleaf pine and dry oak sand hill habitats. It is considered a keystone species because they dig deep burrows that provide shelter to them as well as many other animals. Habitat loss, fragmentation, and disease are major threats and have caused this species to be federally listed as a threatened species under the Endangered Species Act (ESA). Disease is a major threat to the gopher tortoise’s survival, and with declining populations, the need to investigate pathogens is crucial. Herpesvirus, is known to contribute to upper respiratory tract diseases (URTD) in G. polyphemus and is the primary focus of this project. Due to high mutation rates in the virus, a modified version of PCR, nested PCR, was conducted on eye and nose swabs and blood samples obtained from G. polyphemus to detect the presence of the alpha herpesvirus pathogen. The positive samples were then sent for genetic sequencing to confirm the occurrence of the pathogen. The detectability of Herpesvirus in eye and nose swabs was compared to blood and lymph samples and statistical tests concluded that both sample types had the same detectability.