Blair Sterba-Boatwright

Novel application of a statistical technique, Random Forests, in a bacterial source tracking study

In this study, data from bacterial source tracking (BST) analysis using antibiotic resistance profiles were examined using two statistical techniques, Random Forests (RF) and discriminant analysis (DA) to determine sources of fecal contamination of a Texas water body. Cow Trap and Cedar Lakes are potential oyster harvesting waters located in Brazoria County, Texas, that have been listed as impaired for bacteria on the 2004 Texas 303(d) list. Unknown source Escherichia coli were isolated from water samples collected in the study area during two sampling events. Isolates were confirmed as E. coli using carbon source utilization profiles and then analyzed via ARA, following the Kirby-Bauer disk diffusion method. Zone diameters from ARA profiles were analyzed with both DA and RF. Using a two-way classification (human vs nonhuman), both DA and RF categorized over 90% of the 299 unknown source isolates as a nonhuman source. The average rates of correct classification (ARCCs) for the library of 1172 isolates using DA and RF were 74.6% and 82.3%, respectively. ARCCs from RF ranged from 7.7 to 12.0% higher than those from DA. Rates of correct classification (RCCs) for individual sources classified with RF ranged from 23.2 to 0.2% higher than those of DA, with a mean difference of 9.0%. Additional evidence for the outperformance of DA by RF was found in the comparison of training and test set ARCCs and examination of specific disputed isolates; RF produced higher ARCCs (ranging from 8 to 13% higher) than DA for all 1000 trials (excluding the two-way classification, in which RF outperformed DA 999 out of 1000 times). This is of practical significance for analysis of bacterial source tracking data. Overall, based on both DA and RF results, migratory birds were found to be the source of the largest portion of the unknown E. coli isolates. This study is the first known published application of Random Forests in the field of BST.

The ontogenetic scaling of bite force and head size in loggerhead sea turtles (Caretta caretta): implications for durophagy in neritic, benthic habitats

SUMMARY Ontogenetic studies of vertebrate feeding performance can help address questions relevant to foraging ecology. Feeding morphology and performance can either limit access to food resources or open up new trophic niches in both aquatic and terrestrial systems. Loggerhead sea turtles are long-lived vertebrates with complex life histories that are marked by an ontogenetic shift from an oceanic habitat to a coastal neritic habitat, and a transition from soft oceanic prey to hard, benthic prey. Although considered durophagous and strong biters, bite performance has not been measured in loggerheads, nor has the ontogeny of bite performance been characterized. In the present study, we collected measurements of bite force in loggerhead turtles from hatchlings to adults. When subadults reach the body size at which the ontogenetic shift occurs, their crushing capability is great enough for them to consume numerous species of hard benthic prey of small sizes. As loggerheads mature and bite performance increases, larger and harder benthic prey become accessible. Loggerhead bite performance eventually surpasses the crushing capability of other durophagous carnivores, thereby potentially reducing competition for hard benthic prey. The increasing bite performance and accompanying changes in morphology of the head and jaws are likely an effective mechanism for resource partitioning and decreasing trophic competition. Simultaneous measurements of body and head size and the use of non-linear reduced major axis regression show that bite force increases with significant positive allometry relative to body size (straight carapace length, straight carapace width and mass) and head size (head width, height and length). Simple correlation showed that all recorded morphometrics were good predictors of measured bite performance, but an AICc-based weighted regression showed that body size (straight carapace width followed by straight carapace length and mass, respectively) were more likely predictors of bite force than head size morphometrics (head width and head length).

Updating a gas dynamics model using estimates for California sea lions (Zalophus californianus)

Theoretical models are used to predict how breath-hold diving vertebrates manage O2, CO2, and N2 while underwater. One recent gas dynamics model used available lung and tracheal compliance data from various species. As variation in respiratory compliance significantly affects alveolar compression and pulmonary shunt, the current study objective was to evaluate changes in model output when using species-specific parameters from California sea lions (Zalophus californianus). We explored the effects of lung and dead space compliance on the uptake of N2, O2, and CO2 in various tissues during a series of hypothetical dives. The updated parameters allowed for increased compliance of the lungs and an increased stiffness in the trachea. When comparing updated model output with a model using previous compliance values, there was a large decrease in N2 uptake but little change in O2 and CO2 levels. Therefore, previous models may overestimate N2 tensions and the risk of gas-related disease, such as decompression sickness (DCS), in marine mammals.

Euclidean distance matrices: special subsets, systems of coordinates and multibalanced matrices

In this paper we present special subsets of positive semidefinite matrices where the linear function k becomes a geometric similarity and its inverse can be easily computed. The images of these special subsets are characterized geometrically. We also study the systems of coordinates for spherical matrices and at the end, we introduce the class of multibalanced distance matrices.

Water quality dynamics in an urbanizing subtropical estuary(Oso Bay, Texas)

Results are presented from a study of water quality dynamics in a shallow subtropical estuary, Oso Bay, Texas, which has a watershed that has undergone extensive urbanization in recent decades. High inorganic nutrient, dissolved organic matter and chlorophyll concentrations, as well as low pH (<8), were observed in a region of Oso Bay that receives wastewater effluent. Despite being shallow (<1 m) and subjected to strong winds on a regular basis, this region also exhibited episodic hypoxia/anoxia. The low oxygen and pH conditions are likely to impose significant stress on benthic organisms and nekton in the affected area. Signatures of eutrophied water were occasionally observed at the mouth of Oso Bay, suggesting that it may be exported to adjacent Corpus Christi Bay and contribute to seasonal hypoxia development in that system as well. These results argue for wastewater nutrient input reductions in order to alleviate the symptoms of eutrophication.

Ligation of the left aorta in alligators affects acid–base balance: A role for the R → L shunt

This study investigated the effects of preventing bulk flow from the right ventricle to the body via the left aorta (LAo; right to left shunt, R→L) on acid-base status in alligators following feeding, during long-term fasting and a cold temperature exposure. Post-feeding pHv and [Formula: see text] were not significantly different between S and C. Post-feeding pHv increased in both groups of alligators, but not significantly. During fasting, all acid-base variables were similar between the two groups of alligators. A 10 °C reduction in environmental temperature resulted in a significant difference in pHv and HCO3- between S and C. Both pHv and HCO3- were significantly higher in C animals. PV(CO2) significantly decreased in both groups during the cold exposure. Preventing the R→L shunt via the LAo had significant effects on acid-base balance in alligators indicating incomplete compensation for its loss and a role for the LAo in metabolic homeostasis.

Estimated Increase in Inundation Probability with Confidence Intervals for Galveston, Texas

This study uses bootstrap methods to estimate confidence intervals for increases in inundation probability at the Pier 21 tide gauge in Galveston, Texas. The local surge is modeled using the generalized extreme value (GEV) distribution. Resamples of the historical record are created, and a GEV model is fitted to each resample. This ensemble of models is then used to estimate future water level exceedance probabilities under two possible sea level rise scenarios, a conservative linear continuation of the past centurys trend, and a scenario based on the upper limit of the sea level range in the IPCC AR4 report, i.e. the A1FI scenario. The distribution of future exceedance probabilities is trimmed to estimate 90% and 95% confidence intervals around the estimated proportional change in annual water level exceedance probabilities by 2100. The study shows that even under the conservative scenario and using the wider 95% intervals, the frequency of surges of 1.1 m (current return period of 16 years) becomes at least 4 times as common by the end of the century.

Survival, Tag Retention, and Growth of Spot and Mummichog following PIT Tag Implantation

AbstractWe conducted three laboratory studies to determine the effects of surgically implanted, passive integrated transponder (PIT) tags on survival, tag retention, and growth in two abundant estuarine fishes. The effects of the 12.5-mm PIT tags were examined in Spot Leiostomus xanthurus, and the effects of the 12.5-mm and 8.4-mm tags were examined in Mummichog Fundulus heteroclitus. For each experiment, Spot and Mummichogs were divided into three size-groups: small, medium, and large. Tagged Spot had lower survival rates than the untagged conspecifics with the exception of the larger Spot, where there was no difference in survival rates. Large Spot also had the highest tag retention (86%) and tagging “success” (i.e., 80% survived and retained their tag). There was no significant difference in the survival rate between the 12.5-mm tagged and untagged Mummichogs; there was no significant effect of Mummichog size on survival, tag retention, or success; and success for all 12.5-mm tagged Mummichogs was 87%....