Browsing by Subject "South Texas"
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Item Activity and kinetics of microbial extracellular enzymes in organic-poor sands of a south Texas estuary(2009-08) Souza, Afonso Cesar Rezende de, 1968-; Gardner, Wayne Stanley, 1941-; Pease, Tamara KayeThe respective kinetics of bacterial leucine aminopeptidase and [beta]-glucosidase activities were investigated to improve understanding of factors controlling activity and hydrolytic capacity in estuarine organic-poor sands. Depth distributions of enzyme activity and bulk organic matter content were determined in sediments of Aransas Bay and Copano Bay Texas, to investigate enzyme dynamics as related to the geochemical properties of the sediment. Vertical profiles of activity in sediment showed that the enzymes were more active at the surface and that the potential hydrolysis rate of leucine aminopeptidase was higher than that of [beta]-glucosidase. Vertical patterns of enzyme activity correlated (weakly) with variations in sediment organic matter (TOC, TN, and carbohydrates) content. Enrichments of sediment samples with monomeric organic compounds and inorganic nutrients did not affect leucine aminopeptidase and [beta]-glucosidase activities in short- and long-term incubations. Enzyme activity was independent of nutrient availability and suggested that microbial communities were not nutrient-limited. Time-course assays of bacterial hydrolysis of TOC, TN, and carbohydrates provided information about how substrate limitation may affect enzyme activity. Positive correlations between bulk TOC and TN content and enzyme activity indicated enzyme dependence on polymeric substrate content. Induction of enzyme activity after sediment enrichments with specific labile compounds confirmed the importance of available organic substrate to enzyme hydrolysis efficiency. A kinetic approach established the occurrence of enzyme inhibition and its effects on enzyme hydrolytic capacity. The addition of a specific-enzyme substrate to sediment samples modified enzyme parameters and indicated that a substrate-reversible type of inhibitor could reduce enzyme hydrolytic capacity. The addition of polyphenol, as a natural inhibitor of enzyme activity, to the sediment resulted in a concomitant reduction of leucine aminopeptidase activity and ammonium regeneration rate, and thus demonstrated a close coupling between enzyme activity and sediment ammonium regeneration. These research results demonstrate the dynamic nature of the hydrolytic enzymes, provide information about the mechanisms of induction and inhibition of activity, and demonstrate some implications of reducing the hydrolytic capacity to organic matter decomposition and nutrient regeneration rates.Item Algal biofuels : the effect of temperature on algal growth and lipid content(2009-08) Klenzendorf, Stephanie Marie; Marshall, Jill Ann; Mehdy, Mona Cynthia, 1955-; Sathasivan, KanagasabapathiReplacing fossil fuels with algae, a renewable resource, is an exciting possibility. This study evaluates the algae found in South Texas brackish water ponds used for aquaculture of fish as a possible source of biofuels. Samples of algae from these ponds were cultured at varying temperatures ranging from 15.5ºC to 36.5ºC. High levels of growth were observed at 20.5ºC and the highest lipid content was measured at 23.0ºC. Temperature was also a factor in the distribution of microalgal taxa throughout the temperature gradient. This information will be added to the growing body of research investigating similar cultures of algae for future biofuel production.Item The Borderlanders(2009-12) Rodriguez, Marcel Bernard; Stekler, Paul Jeffrey; Perez, Domino; Ramirez-Berg, CharlesThe following report describes the pre-production, production, and post-production of the short film, The Borderlanders, set and shot in South Texas. Its story centers on an immigrant youth who tries to escape the tensions that arise in one family coming together after many years of forced separation because of current immigration policies. It is a meditation on family dynamics and the intimate politics of the border. The report discusses the thought process behind creating images of Latinos in film, the writing of the film, and analyzes the creative choices that gave shape to the film. The original screenplay is included as well as the credits.Item The campus climate of a border HSI : redefining Latino student success(2011-05) Cortez, Laura Jean; Sáenz, Victor B.; Vincent, Gregory J.; Reddick, Richard J.; Rodriguez, Victoria E.; Yamamura, Erica K.The number of Hispanic-Serving Institutions (HSIs) is on the rise. Research suggests that institutions designated as HSIs graduate over fifty percent of Latinos enrolled in college (Santiago, 2006). However, few studies have examined the campus climate of HSIs and how such climate may influence the degree attainment of first-generation, Mexican American students. Considering the instrumental role HSIs have had in advancing the number of Latinos in postsecondary education, this study investigates the campus climate of an HSI along the U.S.-Mexico Border. By utilizing the theoretical frameworks of funds of knowledge (Moll, Amanti, Neff & Gonzalez, 1992) and organizational habitus (McDonough, 1997) this qualitative study involved first-generation, Mexican American students, faculty, and administrators from the University of Texas-Pan American (UTPA). Data collection methods included: student focus groups, individual interviews, observations, reflective notes and a review of relevant documents. Instrumentation used for this study incorporated a student questionnaire as well as pre-established interview questions. Findings revealed students’ perceptions of a Border HSIs, the experiences they describe as helpful in allowing them to obtain a degree; and the institutional characteristics faculty and administrators found critical in allowing first-generation, Mexican American students to persist. This study builds upon a pilot conducted in 2009-2010, that assessed Latino students’ perceptions of HSIs. The goal of this study is 1) to contribute to the literature on first-generation, Mexican American student success and 2) to further enrich our knowledge about the campus climate of Border HSIs and their role in degree attainment of Latinos.Item Diffusion of Innovation: The Introduction of a Point-Of-Use Ceramic Water Filter to South Texas Colonia ResidentsBuentello, Sara A.; Kilburn, John C.People living in South Texas colonias continue to face developing world living conditions. Many residents of the colonias still live without basic and fundamental utilities including running water in their homes. Worldwide lack of access to clean running water is a major social problem and found in new colonias. Research has found that point-of-use ceramic water filters (CWFs) are a viable and cost effective way to purify water and developing countries throughout the world use them today. This study employs Everett Rogers’s 1964 Diffusion of Innovation Theory. Rogers’s theory has been applied in countless studies to analyze the processes through which communities adopt new technologies or practices. One adoption technology, CWFs are made by a facility in the general area in which the residents interviewed for this study live. Results found that residents were interested in the CWF but had not been introduced to the filter and were unaware that a filter making facility was near their homes. While the focus of this study was to determine whether residents would adopt CWF technology, what came into question was why the innovation had not diffused. Research has found that a major reason attributed to a failure to diffuse is that outreach services do not rapidly adapt to the creation of new colonia residents through contact and education about the water filter. Potential adopters did show interest in the CWF when its use was explained as a part of this study. State and local resources need to be deployed to prevent communication of water-borne diseases and preserve new colonia resident’s health.Item Ecotoxicological simulation modeling: effects of agricultural chemical exposure on wintering burrowing owls(Texas A&M University, 2008-10-10) Engelman, Catherine AllegraThe western burrowing owl, Athene cunicularia hypugaea, is a Federal Species of Concern, whose numbers and range have been drastically reduced from historic levels in Texas. Burrowing owls roost and forage in agricultural areas, and it has been hypothesized that exposure to insecticides may be a factor in the decline of their population. Burrowing owls wintering in southern Texas use agricultural culverts in cotton fields as roost sites, which may increase their risk of exposure to agricultural chemicals, either through ingestion of contaminated prey or through dermal exposure to agricultural runoff. Simulation modeling was used to characterize the risks to individual burrowing owls wintering in agricultural landscapes in southern Texas due to effects of exposure to insecticides or other agricultural chemicals. The simulation model was created using Stella? VII software (High Performance Systems, Inc., New Hampshire, USA). The model is broken into four submodels simulating (1) foraging behavior of burrowing owls, (2) chemical applications to crops, (3) chemical transfer and fate in the crop soil and prey items, and (4) chemical exposure in the burrowing owl. This model was used to evaluate (1) which components of the model most affect the endpoints, (2) the relationship between increased concentrations of agricultural chemicals in culverts and subsequent lethal and sublethal effects from dermal exposure to agricultural runoff, and (3) which agricultural chemicals have the greatest potential to cause adverse effects in burrowing owls. Model results suggested (1) the half-lives of agricultural chemicals in birds caused the most variation in the results, and data gaps exist for several important model components (2), exposure to increased concentrations of agricultural chemicals in culverts is unlikely to result in lethal effects, but is likely to lead to sublethal effects in burrowing owls, and (3) the chemicals with the greatest potential to negatively affect burrowing owls wintering in southern Texas are the OP insecticides chlorpyrifos, dicrotophos, and disulfoton, the oxadiazine insecticide indoxacarb, the herbicide trifluralin, and the defoliants tribufos and paraquat. The results of this model demonstrate the usefulness of simulation modeling to guide future research related to the conservation of burrowing owls.Item From vaqueros to mafiosos : a community history of drug trafficking in rural South Texas(2011-05) Guerra, Santiago Ivan, 1982-; Menchaca, Martha; Hartigan, John; Limon, Jose E.; Foley, Doug; Martinez, AnneMy dissertation, From Vaqueros to Mafiosos: A Community History of Drug Trafficking in Rural South Texas is an ethnographic study of the impact of the drug trade in South Texas, with a specific focus on Starr County. This dissertation examines drug trafficking along the U.S-Mexico Border at two levels of analysis. First, through historical ethnography, I provide a cultural history of South Texas, as well as a specific history of drug trafficking in Starr County. In doing so, I highlight the different trafficking practices that emerge throughout South Texas’ history, and I document the social changes that develop in Starr County as a result of these illicit practices. The second half of my dissertation, however, is devoted to a contemporary analysis of the impact of the drug trade on the border region by analyzing important social practices in Starr County relating to drug abuse, policing and the criminal justice system, youth socialization and family life. Through ethnography I present the devastating effects of the drug trade and border policing on this Mexican American border community in rural South Texas.Item "History should be told as a fact": Elena Zamora O'Shea's reconstruction of the Texas past(2010-05) Pasternack, Natasha Miller; Cordova, Cary, 1970-; Gonzalez, John M.This report examines the life and works of Elena Zamora O'Shea, reading them as a form of resistance to the dominant narrative of Anglo conquest in south Texas.Item Is That What I Sound Like When I Speak?: Attitudes Towards Spanish, English, and Code-Switching in Two Texas Border Towns(2013-08-28) Rangel, NatalieThe present study observes and compares the language attitudes towards standard English, standard Spanish, and code-switching in two U.S. and Mexico border cities (Laredo and Edinburg) by employing the matched-guise technique Three attribute dimensions (solidarity, status, and personal appeal) were used by participants to evaluate the three varieties in question. Situated just 150 miles from one another, Laredo and Edinburg are both border cities with a majority Hispanic-origin population. Yet, the histories of Laredo and Edinburg differ: while Laredo was a fully established community before the arrival of the Anglos in the 19^(th) century and succeeded in protecting its lands from Anglo encroachment, the Hispanic population where Edinburg is located suffered land loss during the same time . The present study examined if these historical differences have had consequences on the contemporary linguistic attitudes in these two cities. For the matched-guise experiment, an original code-switching recording was produced in Spanish and English versions. These three texts went through grammaticality testing and were then recorded by four Mexican American bilingual speakers, two males and two females. Ninety-six participants from Laredo and ninety-one participants from Edinburg answered a demographic questionnaire and then were told to listen and evaluate each voice on a list of characteristics grouped into the three dimensions mentioned above (solidarity, status, and personal appeal), unaware that they were in fact listening to bilingual speakers speaking in different language varieties. Code-switching received the lowest evaluations in all three dimensions. Also, Spanish and English were judged relatively the same in status and personal appeal, but Spanish ranked much higher than both code-switching and standard English in solidarity. When the variables of speaker and student gender were considered, differences emerged in the evaluations within and between both cities. In regards to the differences found between locations, female students from Edinburg appear to be more tolerant towards code-switching than female students in Laredo, particularly when the speaker is male. Edinburg males also appear to evaluate females who speak English higher than Laredo male students. Yet at the same time these same male students evaluate males who use English less favorably in solidarity and higher in personal appeal, while the Laredo males display the inverse tendency. The fact that differences between locations were found upon considering the speakers? and students? gender indicates that differing linguistic attitudes exist among residents in the South Texas region and deserves further investigation.Item Lithologic heterogeneity of the Eagle Ford Formation, South Texas(2014-05) Ergene, Suzan Muge; Milliken, K. L.Grain assemblages in organic-rich mudrocks of the Eagle Ford Formation of South Texas are assessed to determine the relative contributions of intra- and extrabasinal sediment sources, with the ultimate goal of producing data of relevance to prediction of diagenetic pathways. Integrated light microscopy, BSE imaging, and X-ray mapping reveal a mixed grain assemblage of calcareous allochems, biosiliceous grains (radiolaria), quartz, feldspar, lithics, and clay minerals. Dominant fossils are pelagic and benthic foraminifers and thin-walled and prismatic mollusks; echinoderms, calcispheres, and oysters are present. Early-formed authigenic minerals, including calcite, kaolinite, dolomite, albite, pyrite, quartz, and Ca-phosphate, some reworked, add to the overall lithologic heterogeneity. Point counting of images produced using energy-dispersive X-ray mapping in the SEM provides observations at a scale appropriate to classifying the mudrocks based on the composition of the grain assemblage, although grains and other crystals of clay-size cannot be fully characterized even with the SEM. Each sample is plotted on a triangle, whose vertices correspond to terrigenous and volcanic grains (extrabasinal components), calcareous allochems, and biosiliceous grains. As a subequal mix of grains of intrabasinal and extrabasinal origins the detrital grain assemblage of the Eagle Ford, presents a formidable challenge to the task of lithologic classification of this unit, as neither conventional limestone nor sandstone classifications can be readily applied. The abundant marine skeletal debris in the Eagle Ford is accompanied by abundant calcite cementation and the dissolution and replacement of biosiliceous debris is accompanied by authigenic quartz, suggesting that mudrock grain classification has potential for yielding diagenetic predictions.Item Middle-Hauterivian to Lower-Campanian sequence stratigraphy and stable isotope geochemistry of the Comanche platform, south Texas(2011-05) Phelps, Ryan Matthew, 1982-; Kerans, C. (Charles), 1954-; Loucks, Robert G.; Janson, Xavier; Scott, Robert W.; Fisher, William L.; Quinn, Terrence M.Carbonate platforms contain a wealth of information regarding the changing biota, sea level, ocean-chemistry, and climate of the Cretaceous Period. The Comanche platform of the northern Gulf of Mexico represents a vast, long-lived carbonate system that extended from west Texas through the Florida panhandle. In central and south Texas, excellent outcrops and an extensive suite of subsurface data provide an opportunity to document the evolution of this system, from the shoreline to the shelf-margin and slope. This study examines the changing facies, platform morphologies, and shelf-margin architectures of the mixed carbonate-siliciclastic, middle-Hauterivian to lower-Campanian interval. Stratigraphic results are integrated with stable-isotope geochemistry to document the detrimental effects of oceanic anoxic events on the carbonate platform. Seven second-order, transgressive-regressive supersequences of 3-14 Myr duration are defined in south Texas using sequence stratigraphic analysis of shelf-interior facies successions. Second-order supersequences are subdivided into several third-order depositional sequences of 1-3 Myr duration. In these sequences, facies proportions and stratal geometries of the shelf-interior are found to be the result of changing platform morphology and temporal evolution from distally-steepened ramp to rimmed-shelf depositional profiles. Shelf-margin trajectories, stratigraphic architectures, and facies proportions are a function of long-term accommodation trends expressed in second-order supersequences. These characteristics are modified by lateral variability in the underlying structural/tectonic setting and localized syndepositional faulting. The stratigraphic equivalents of oceanic anoxic events 1a, 1b, 1d, 2, and 3 are documented in the Cretaceous section of south Texas. These oceanic anoxic events coincided with maximum flooding zones of supersequences and are linked to carbonate platform drowning events on four separate occasions. The occurrence of oceanic anoxic events is found to be a fundamental driver of carbonate platform morphology, faunal composition, and facies evolution in transgressive-regressive supersequences of the northern Gulf of Mexico.Item Population Dynamics of Plain Chachalacas in the Lower Rio Grande Valley(2011-02-22) Gandaria, Adan G.The Lower Rio Grande Valley (LRGV) of Texas is an ecologically diverse region in the United States and marks the northernmost extension for many tropical species of plants and animals. Since the early 1900s, 95% of the native Tamaulipan brushlands have been cleared due to agricultural practices and urban development. The plain chachalaca (Ortalis vetula) is a medium sized bird endemic to the native brushlands of the LRGV. In 2003, I trapped and radio-tagged 29 birds (16 males, 13 females) to evaluate the effects of fragmentation on the population dynamics (i.e., survival, mortality, and movements) of this brushland species. My study objectives were to estimate (1) seasonal survival of chachalacas by sex, and (2) ranges, core areas, and movements using radio telemetry. Mammalian predation (43%, n = 6) and unknown (43%, n = 6) deaths accounted for the majority of mortality observed. I found no difference (P > 0.05) in estimated 8-month survival (December 2003-July 2004) between males (S = 0.364, SE = 0.132) and females (S = 0.405, SE = 0.153). In comparing seasonal survival for all birds (males and females combined), I observed a difference (P < 0.05) in survival between the nesting (S = 0.414, SE = 0.103) and breeding seasons (S = 0.917, SE = 0.079). Female ranges (x? = 117 ha, range = 42?177 ha) and core areas (x? = 23 ha, range = 5?46 ha) during the nesting season were larger than male ranges (x? = 41 ha, range = 31?46 ha) and core areas (x? =10 ha, range = 7?14 ha) during the same period. During the breeding season, female ranges (x? = 59 ha, range = 10?188 ha) and core areas (x? = 9 ha, range = 2?33 ha) were similar to male ranges (x? = 48 ha, range = 4?130 ha) and core areas (x? = 9 ha, range = 1?23 ha). Mean distances between seasons were similar for both sexes (females, nesting, x? = 486, breeding, x? = 345; males, nesting, x? = 184, breeding, x? = 292), though females distances generally were greater. Dispersal defined as movement off the Santa Ana National Wildlife Refuge was observed for 3 birds. In 2 cases, a radio-tagged female and male were observed crossing the Rio Grande River (approximately 100-m wide) to habitat in Mexico. Study results suggested mammalian predation may limit the growth of chachalaca populations. Though land use changes such as agricultural uses may not directly limit chachalaca populations in providing cover and food, concentration of populations in remnant native brushlands may serve as ecological ?sinks? to the species. Greater range and movement data observed in my study may be attributed to suboptimal habitat (i.e., increased fragmentation) for plain chachalacas.Item Quantification of potential arsenic bioavailability in spatially varying Geologic Environments at the Watershed Scale Using Chelating Resins(Texas A&M University, 2004-09-30) Lake, Graciela EstherPotential arsenic toxicity in different geologic environments is dependent on total arsenic concentration and arsenic bioavailability. It is important to identify the geologic environments that may sequester arsenic because these systems can act as long-term sources for arsenic as well as retard transport and limit toxicity. Bioavailability is defined as the readiness of a compound or element to be taken up by organisms (Gregorich et al., 2001), while potential bioavailability is possible uptake of a compound or element by organisms. The objective of this research is to quantify the potential bioavailability of arsenic in laboratory microcosms and in different geologic environments in the Nueces and San Antonio River Watersheds, Texas, using a chelating resin as an infinite sink. To assess the applicability of chelating resins to estimate potential arsenic bioavailability in the field, iron-loaded DOWEX M4195 resin was used to extract arsenic from solutions and sediments (pond sediment, river sediment, and ephemeral stream sediment). The average percentage of arsenic sorbed from solution was 66% ? 0.16. Competition studies between arsenate, phosphate, and vanadate suggest there is moderate competition, reducing overall arsenic sorption to the resin in the presence of competing ions. Iron-loaded resin was then exposed to sediment samples spiked with increasing amounts of arsenic over 15, 30, 60 and 90 days. Results of the sediment study showed 1) increased arsenic sorption to the resin over time, 2) small variations of potential bioavailable arsenic among geologically different sediments, and 3) evidence of arsenic sequestration. Field devices that housed iron-loaded resin were used to extract potentially bioavailable arsenic from sediment in six different geologic environments (i.e. lake, river, perennial stream, ephemeral stream, pond, and wetland) in the watersheds over a twenty-eight day period. The wetland (15.7 mmol As/g wet resin) and perennial stream sediments (11.0 mmol As/g wet resin) represented the maximal and minimal calculated potential bioavailability, respectively. However, the potentially bioavailable index calculated from mmol As/g wet resin extracted from field environments and mmol As/ g sediment in digested samples showed sequestration would be high in the wetland environment and high bioavailability in the perennial stream and river environments.Item Quantitative assessment of pore types and pore size distribution across thermal maturity, Eagle Ford Formation, South Texas(2014-08) Pommer, Maxwell Elliott; Milliken, K. L.Scanning electron microscopy of Ar-ion milled samples from the Eagle Ford Formation, South Texas shows that the character and abundance of porosity changes significantly across burial conditions as a result of compaction, cementation, bitumen generation, and generation of secondary porosity within organic matter (OM). Samples displaying a range of compositions and maturities are imaged and quantified to provide insight into the effects of these processes. Porosity in low-maturity samples (Ro~0.5%) is volumetrically dominated (0.1% -12.5% bulk volume, average 6.2%) by relatively large, mostly interparticle, primary mineral-associated pores (median sizes range 35.9-52.7 nm). Larger pores are generally associated with coccolith debris that is commonly aggregated into pellets. Porosity and pore size correlate directly with calcite abundance and inversely with OM volumes. OM is dominantly detrital kerogen "stringers" that range in size and have spatial distributions and character suggestive of detrital origin. Destruction of primary porosity in low-maturity samples has occurred due to compaction of ductile kerogen and clays and, to a minor degree, as a result of cementation and infill of early bitumen. Smaller, secondary OM-hosted pores (median size range 11.1-14.9 nm) volumetrically dominate porosity (0.02%-3.6% bulk volume, average of 1.36%), in most high-maturity samples (Ro~1.2%-1.3%). Mineral-associated pores are present, but are typically smaller (median size range from 20.3-40.6 nm) and less abundant (0.0%-10.0% bulk volume, average of 2.5%) than at low maturity. Abundant mineral-associated porosity is present locally in samples where incursion of primary pore space by bitumen has not occurred. OM within high-maturity samples is distributed more evenly throughout the rock fabric, occupying spaces similar in size and morphology to primary interparticle pores, coating euhedral crystals (probable cements), and filling intraparticle porosity. These observations, and positive correlation between calcite and OM volumes (OM-hosted pore volume included) in samples with dominantly OM-hosted pore networks, suggests that a large portion of OM within high-maturity samples is diagenetic in origin and has filled primary pore space. Destruction of primary porosity in high-maturity samples has occurred through cementation, bitumen infill, and, possibly greater compaction. Additional porosity, however, has been generated through maturation of OM.Item REPRODUCTIVE SUCCESS AND ANNUAL HABITAT PREFERENCE BY RED-SHOULDERED HAWKS IN SOUTHERN TEXAS(2011-05) Strobel, Bradley N.; Boal, Clint W.; Andersen, David E.; Haukos, David A.; Griffis-Kyle, Kerry; Blankenship, TerryIdentifying the vegetation characteristics resulting in habitat use by nesting raptors provides information important to species conservation and management. I examined nesting habitat preference of red-shouldered hawks (Buteo lineatus) using conditional logistic regression on characteristics measured at 27 occupied nest sites and 68 randomly selected unused sites in 2005–2009 in southern Texas. I measured vegetation characteristics of individual trees (nest trees and unused trees) and corresponding surrounding 0.04 ha plots. I evaluated the importance of tree and plot characteristics to nesting-habitat selection by comparing a priori tree-specific and plot-specific models using Akaike‘s Information Criterion corrected for small sample size (AICc). Models with only plot variables carried 14% more weight than models with only center-tree variables. The model-averaged odds ratios indicated red-shouldered hawks selected to nest in taller trees and in areas with higher average diameter at breast height (dbh) than randomly available within the forest stand. Relative to randomly selected areas, each 1-m increase in nest-tree height and 1-cm increase in the plot-average dbh increased the probability of selection by 85% and 10%, respectively. My results indicate characteristics of individual trees and the structure of the 0.04 ha area surrounding the tree, were associated with red-shouldered hawk nesting habitat selection. My results show red-shouldered hawks preferred taller nest trees (average 16.4 m) surrounded by larger diameter trees (average 25.4 cm) relative to the surrounding forest in southern Texas. Preference for taller nest trees by raptors is well documented and suggests an association with increased fitness. Further study is required to understand the mechanism responsible for this preference. Widespread alteration of forest communities combined with the well-documented preference for mature forests by breeding red-shouldered hawks (Buteo lineatus) has caused concern over the conservation of the species. Although habitat preferences of breeding red-shouldered hawks have been well documented, few data describe non-breeding-period habitat selection. I studied the seasonal habitat preferences of 12 adult red-shouldered hawks in southern Texas. I used radio-telemetry to collect >1,800 locations during 3 discrete phenological periods (winter, breeding-spring, and non-breeding-spring). I constructed phenological stage-specific discrete-choice models to compare the proportion of a 0.5-ha circle around each location (used and available) comprised of mature forests, young forests, brush, grass, wetland, and open-water cover types. I used general linear models to assess whether the amount of mature forest covertypes within used areas was dependent upon the sex of the individual, its breeding status, or the time of year the data were collected. During the breeding-spring-period, red-shouldered hawks preferred areas with greater amounts of mature forest cover types (selection ratio = 1.40, 95% CI = 1.16 - 1.69) and higher cover-type richness (selection ratio = 1.10, 95% CI = 1.04 - 1.21). Characteristics associated with habitat use during the breeding-spring-period were different than those associated with winter-period or non-breeding-spring-period habitat selection. Habitat use during the winter was associated with greener vegetation measured using the Normalized Difference Vegetation Index (NDVI), and avoidance of grasslands, brushlands, and wetlands. My data indicate the amount of forested cover types preferred by individual red-shouldered hawks depends upon the sex of the individual as well as its breeding stage (i.e., breeding, non-breeding). Habitat quality is often evaluated based on relative resource preferences, usually by examining disproportionate use of available resources. Alternatively, the Ideal Despotic Distribution hypothesis predicts that given a suite of territories to select from, an individual will select the highest quality territory in regards to its perceived fitness benefit. Presumably, the long-term occupancy rates of specific territories will be positively correlated with their quality. However, the predictions of the ideal despotic distribution hypothesis hinge upon the individual‘s ability to accurately assess territory quality (perfect knowledge), a condition that is difficult to meet under temporally and spatially variant environments. Using a 5-year data set on a resident population of red-shouldered hawks in southern Texas, I examined the predictions of the ideal despotic distribution hypothesis. My results were consistent with the prediction of the ideal despotic distribution hypothesis that the proportion of years a territory supported a nesting attempt was negatively related to the relative nest initiation dates. However, in contrast to the predictions of the ideal despotic distribution hypothesis, my data show that proportion of years a territory supported a nesting attempt was unrelated to the average number of eggs laid and negatively related to the average number of young fledged annually. Whereas the proportion of years a territory supported a nesting attempt varied across territories, the annual reproductive success of breeding red-shouldered hawks varied markedly from year to year and was positively associated with the number of breeding pairs observed. Overall, my results suggest that red-shouldered hawk reproductive success is influenced heavily by stochastic characteristics that violate the ideal despotic distribution hypothesis‘ assumption of perfect knowledge by individuals.Item U-Pb geochronology of the Late Cretaceous Eagle Ford Shale, Texas; defining chronostratigraphic boundaries and volcanic ash source(2014-08) Pierce, John Donald; Fisher, W. L. (William Lawrence), 1932-; Ruppel, Stephen C.The Eagle Ford Shale and equivalent Boquillas Formation (Late Cretaceous) contain abundant volcanic ash beds of varying thickness. These ash beds represent a unique facies that displays a range of sedimentary structures, bed continuity, and diagenetic alteration. They are prominent not only in West Texas outcrops, but also in the subsurface of South Texas where hydrocarbon production is actively occurring. The ash beds have the potential to be used for stratigraphic correlation for understanding early diagenesis and — most importantly — for obtaining high-resolution geochronology, which can then be used for defining depositional rates and chronostratigraphy. Study of the ash beds was conducted at outcrops along U.S. 90, west of Comstock, Texas, the subsurface in Atascosa and Karnes County, and at a construction site in South Austin. Bed thicknesses range from 0.1–33 cm and were collected throughout the entirety of the Eagle Ford succession. Mineral separation yielded abundant non-detrital zircons for U-Pb dating. Dating was conducted using LA-ICP-MS at The University of Texas at Austin, to attain a base level understanding of the age range for the Eagle Ford. High-resolution ages for the base and top of the Eagle Ford were obtained, in addition to radioisotopically defining the Cenomanian-Turonian boundary within the section. U-Pb ages for the Eagle Ford Shale range from Early Cenomanian to Late-Coniacian near Comstock, Mid-Cenomanian to the Turonian-Coniacian boundary in the subsurface, and Early Cenomanian to Late Turonian in Austin area. These findings contrast with many of the regional biostratigraphic studies across the Eagle Ford and indicate a more prolonged period of Eagle Ford deposition than previously observed.Item Understanding college readiness and the role of the community college in South Texas : listening to the voices of public school leaders and parents in three school districts(2009-05) Johnson, Wallace Dodge; Roueche, John E.The researcher/writer of this treatise has used qualitatively based data to develop a better understanding of the perceptions of college readiness initiatives in three public school districts in the service area of a community college in South Texas. The researcher has also used these methods to understand the perceptions of participants in a community based parental outreach program about the subject of college readiness. More specifically, through the use interviews with public school district superintendents, focus groups with educational professionals in the corresponding school districts, and similar focus group interviews with the parent/facilitators in the outreach group; critical issues, incidents, and events have been identified to improve and better inform the processes of college readiness initiatives for the college. The end product of this treatise will help both the researcher/practitioner and the leadership of the college improve their educational service to the community, and add new voices to the character of this service. The researcher as an outsider to the language and culture of the region, has also reflected on his positionality and professional growth within this community through these processes.