UNT Theses and Dissertations - 42 Matching Results

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Biodiversity and Genetic Structure of Benthic Macroinvertebrates along an Altitudinal Gradient: A Comparison of the Windhond and Róbalo River Communities on Navarino Island, Chile

Description: Altitudinal gradients in Sub-Antarctic freshwater systems present unique opportunities to study the effect of distinct environmental gradients on benthic macroinvertebrate community composition and dispersal. This study investigates patterns in biodiversity, dispersal and population genetic structure of benthic macroinvertebrate fauna across an altitudinal gradient between two watersheds on Navarino Island in southern Chile. Patterns in diversity, density, evenness and functional feeding groups were not significantly different across the altitudinal gradient in both the Windhond and Róbalo Rivers. Taxa richness in both rivers generally increased from the headwaters of the river to the mouth, and functional feeding group patterns were consistent with the predictions of the River Continuum Concept. Population genetic structure and gene flow was investigated by sampling the mitochondrial cytochrome oxidase I gene in two invertebrate species with different dispersal strategies. Hyalella simplex (Amphipoda) is an obligate aquatic species, and Meridialaris chiloeense (Ephemeroptera) is an aquatic larvae and a terrestrial winged adult. Contrasting patterns of population genetic structure were observed. Results for Hyalella simplex indicate significant differentiation in genetic structure in the Amphipod populations between watersheds and lower genetic diversity in the Róbalo River samples, which may be a result of instream dispersal barriers. Meridialaris chiloeense exhibited weak population structure but higher genetic diversity, which suggests this species is able to disperse widely as a winged adult.
Date: May 2016
Creator: Pulliam, Lauren
Partner: UNT Libraries

The Effects of Neonicotinoid Exposure on Embryonic Development and Organ Mass in Northern Bobwhite Quail

Description: Since their emergence in the early 1990s, neonicotinoid use has increased exponentially to make them the world's most prevalent insecticides. Although there is considerable research concerning the lethality of neonicotinoids, their sub-lethal and developmental effects are still being explored, especially with regards to non-mammalian species. The goal of this research was to investigate the effects of the neonicotinoid imidacloprid on the morphological and physiological development of northern bobwhite quail (Colinus virginianus). Bobwhite eggs (n = 650) were injected with imidacloprid concentrations of 0 (sham), 10, 50, 100 and 150 grams per kilogram of egg mass, which was administered at day 0 (pre-incubation), 3, 6, 9, or 12 of growth. Embryos were dissected on day 19 when they were weighed, staged, and examined for any overt structural deformities. Embryonic heart, liver, lungs and kidneys were also weighed and preserved for future use. Treated embryos exhibited increased frequency of severely deformed beaks and legs, as well as larger hearts and smaller lungs at the higher dosing concentrations. Some impacts are more pronounced in specific dosing periods, implying that there may be critical windows of development when embryos are highly susceptible to neonicotinoid exposure. This investigation suggests that imidacloprid could play a significant role in chick survival and declining quail populations in treated regions of the country.
Date: May 2016
Creator: Gobeli, Amanda
Partner: UNT Libraries

The Influence of Urban Green Spaces on Declining Bumble Bees (Hymenoptera: Apidae)

Description: Bumble bees (Bombus spp.) are adept pollinators of countless cultivated and wild flowering plants, but many species have experienced declines in recent decades. Though urban sprawl has been implicated as a driving force of such losses, urban green spaces hold the potential to serve as habitat islands for bumble bees. As human populations continue to grow and metropolitan areas become larger, the survival of many bumble bee species will hinge on the identification and implementation of appropriate conservation measures at regional and finer scales. North Texas is home to some the fastest-growing urban areas in the country, including Denton County, as well as at least two declining bumble bee species (B. pensylvanicus and B. fraternus). Using a combination of field , molevular DNA and GIS methods I evaluated the persistence of historic bumble bee species in Denton County, and investigated the genetic structure and connectivity of the populations in these spaces. Field sampling resulted in the discovery of both B. pensylvanicus and B. fraternus in Denton County's urban green spaces. While the relative abundance of B. fraternus in these spaces was significantly lower than historic levels gleaned from museum recors, that of B. pensylvanicus was significantly higher. Statistical analyses found that both bare ground and tree cover surrounding sample sites were negatively associated with numbers of bumble bee individuals and hives detected in these green spaces. Additionally, limited genetic structuring of bumble bee populations was detected, leading to the conclusion that extensive gene flow is occurring across populations in Denton County.
Date: May 2016
Creator: Beckham, Jessica Lorene
Partner: UNT Libraries

Informing Conservation Management Using Genetic Approaches: Greater Sage-grouse and Galápagos Short-eared Owls as Case Studies

Description: Small isolated populations are of particular conservation interest due to their increased extinction risk. This dissertation investigates two small wild bird populations using genetic approaches to inform their conservation. Specifically, one case study investigated a Greater Sage-grouse (Centrocercus urophasianus) population located in northwest Wyoming near Jackson Hole and Grand Teton National Park. Microsatellite data showed that the Jackson sage-grouse population possessed significantly reduced levels of neutral genetic diversity and was isolated from other Wyoming populations. Analysis with single nucleotide polymorphisms (SNPs) and microsatellite data provided further evidence that the population's timing of isolation was relatively recent and most likely due to recent anthropogenic habitat changes. Conservation recommendations include maintaining or increasing the population's current size and reestablishing gene flow with the nearest large population. The second case study investigated the genetic distinctiveness of the Floreana island population of the Galápagos Short-eared Owl (Asio flammeus galapagoensis). Mitochondrial DNA sequence data did not detect differences across nine island populations, yet microsatellite and morphometric data indicated that limited gene flow existed with the population and surrounding island populations, which appeared asymmetric in direction from Floreana to Santa Cruz with no indication of gene flow into Floreana. These results have important conservation implications and recommend that the Floreana Short-eared Owl population be held in captivity during the rodenticide application planned for an ecosystem restoration project in 2018. The population is less likely to receive immigrants from surrounding island populations if negatively effected by feeding on poisoned rodents.
Date: May 2016
Creator: Schulwitz, Sarah E
Partner: UNT Libraries

Residential Grid-Connected Photovoltaics Adoption in North Central Texas: Lessons from the Solarize Plano Project

Description: Residential Grid-Connected Photovoltaics (GPV) systems hold remarkable promise in their potential to reduce energy use, air pollution, greenhouse gas emissions, and energy costs to consumers, while also providing grid efficiency and demand-side management benefits to utilities. Broader adoption of customer-sited GPV also has the potential to transform the traditional model of electricity generation and delivery. Interest and activity has grown in recent years to promote GPV in north central Texas. This study employs a mixed methods design to better understand the status of residential GPV adoption in the DFW area, and those factors influencing a homeowner's decision of whether or not to install a system. Basic metrics are summarized, including installation numbers, distribution and socio-demographic information for the case study city of Plano, the DFW region, Texas, and the United States. Qualitative interview methods are used to gain an in-depth understanding of the factors influencing adoption for the Solarize Plano case study participants; to evaluate the effectiveness of the Solarize Plano program; and to identify concepts that may be regionally relevant. Recommendations are presented for additional research that may advance GPV adoption in north central Texas.
Date: August 2016
Creator: Jack, Katherine G.
Partner: UNT Libraries

Developing a Forest Gap Model to Be Applied to a Watershed-scaled Landscape in the Cross Timbers Ecoregion Using a Topographic Wetness Index

Description: A method was developed for extending a fine-scaled forest gap model to a watershed-scaled landscape, using the Eastern Cross Timbers ecoregion as a case study for the method. A topographic wetness index calculated from digital elevation data was used as a measure of hydrologic across the modeled landscape, and the gap model modified to have with a topographically-based hydrologic input parameter. The model was parameterized by terrain type units that were defined using combinations of USDA soil series and classes of the topographic wetness index. A number of issues regarding the sources, grid resolutions, and processing methods of the digital elevation data are addressed in this application of the topographic wetness index. Three different grid sizes, 5, 10, and 29 meter, from both LiDAR-derived and contour-derived elevation grids were used, and the grids were processed using both single-directional flow algorithm and bi-directional flow algorithm. The result of these different grids were compared and analyzed in context of their application in defining terrain types for the forest gap model. Refinements were made in the timescale of gap model’s weather model, converting it into a daily weather generator, in order to incorporate the effects of the new topographic/hydrologic input parameter. The precipitation model was converted to use a Markov model to initiate a sequence of wet and dry days for each month, and then daily precipitation amounts were determined using a gamma distribution. The output of the new precipitation model was analyzed and compared with a 100-year history of daily weather records at daily, monthly, and annual timescales. Model assumptions and requirements for biological parameters were thoroughly investigated and questioned. Often these biological parameters are based on little more than assumptions and intuition. An effort to base as many of the model’s biological parameters on measured data was made, including a new ...
Date: August 2014
Creator: Goetz, Heinrich
Partner: UNT Libraries

Effects of Macrophyte Functional Diversity on Taxonomic and Functional Diversity and Stability of Tropical Floodplain Fish Assemblages

Description: Multiple dimensions of biodiversity within and across producer and consumer guilds in the food web affect an ecosystem’s functionality and stability. Tropical and subtropical aquatic ecosystems, which are extremely diverse, have received much less attention than terrestrial ecosystems in regards to the effects of biodiversity on ecosystem functioning. We conducted a field experiment that tested for effects of macrophyte functional diversity on diversity and stability of associated fish assemblages in floodplain lakes of the Upper Paraná River floodplain, Brazil. Three levels of macrophyte functional diversity were maintained through time in five floodplain lakes and response variables included various components of fish taxonomic and functional diversity and stability. Components of functional diversity of fish assemblages were quantified using a suite of ecomorphological traits that relate to foraging and habitat use. Response variables primarily distinguished macrophyte treatments from the control. Macrophyte treatments had, on average, double the number of species and total abundance than the control treatment, but only limited effects on stability. The high diversity treatment was essentially nested within the low diversity for assemblage structure and had similar or even slightly lower levels of species richness and abundance in most cases. Gymnotiformes and young-of-year were diverse and relatively abundant in macrophyte treatments contributing to the large differences in diversity between macrophyte and control treatments. Higher fish diversity in structured habitats compared to more homogenous habitats is likely associated with increased ecomorphological diversity to exploit heterogeneous microhabitats and resources provided by the macrophytes.
Date: August 2015
Creator: Treviño, Jessica Marie
Partner: UNT Libraries

Measuring Atmospheric Ozone and Nitrogen Dioxide Concentration by Differential Optical Absorption Spectroscopy

Description: The main objective was to develop a procedure based on differential optical absorption spectroscopy (DOAS) to measure atmospheric total column of ozone, using the automated instrument developed at the University of North Texas (UNT) by Nebgen in 2006. This project also explored the ability of this instrument to provide measurements of atmospheric total column nitrogen dioxide. The instrument is located on top of UNT’s Environmental Education, Science and Technology Building. It employs a low cost spectrometer coupled with fiber optics, which are aimed at the sun to collect solar radiation. Measurements taken throughout the day with this instrument exhibited a large variability. The DOAS procedure derives total column ozone from the analysis of daily DOAS Langley plots. This plot relates the measured differential column to the airmass factor. The use of such plots is conditioned by the time the concentration of ozone remains constant. Observations of ozone are typically conducted throughout the day. Observations of total column ozone were conducted for 5 months. Values were derived from both DOAS and Nebgen’s procedure and compared to satellite data. Although differences observed from both procedures to satellite data were similar, the variability found in measurements was reduced from 70 Dobson units, with Nebgen’s procedure, to 4 Dobson units, with the DOAS procedure.A methodology to measure atmospheric nitrogen dioxide using DOAS was also investigated. Although a similar approach to ozone measurements could be applied, it was found that such measurements were limited by the amount of solar radiation collected by the instrument. Observations of nitrogen dioxide are typically conducted near sunrise or sunset, when solar radiation experiences most of the atmospheric absorption.
Date: December 2011
Creator: Jerez, Carlos J.
Partner: UNT Libraries

Dynamics of Stream Fish Metacommunities in Response to Drought and Re-connectivity

Description: This dissertation investigates the spatio-temporal dynamics of intermittent stream fish metacommunities in response drought-induced fragmentation and re-connectivity using both field and experimental approaches. A detailed field study was conducted in two streams and included pre-drought, drought, and post-drought hydrological periods. Fish assemblages and metacommunity structure responded strongly to changes in hydrological conditions with dramatic declines in species richness and abundance during prolonged drought. Return of stream flows resulted in a trend toward recovery but ultimately assemblages failed to fully recover. Differential mortality, dispersal, recruitment among species indicates species specific responses to hydrologic fragmentation, connectivity, and habitat refugia. Two manipulative experiments tested the effects of drought conditions on realistic fish assemblages. Fishes responded strongly to drought conditions in which deeper pools acted as refugia, harboring greater numbers of fish. Variability in assemblage structure and movement patterns among stream pools indicated species specific habitat preferences in response predation, resource competition, and desiccation. Connecting stream flows mediated the impacts of drought conditions and metacommunity dynamics in both experiments. Results from field and experimental studies indicate that stream fish metacommunities are influenced by changes in hydrological conditions and that the timing, duration, and magnitude of drought-induced fragmentation and reconnecting stream flows have important consequences metacommunity dynamics.
Date: August 2015
Creator: Driver, Lucas J.
Partner: UNT Libraries

Spatially Explicit Modeling of West Nile Virus Risk Using Environmental Data

Description: West Nile virus (WNV) is an emerging infectious disease that has widespread implications for public health practitioners across the world. Within a few years of its arrival in the United States the virus had spread across the North American continent. This research focuses on the development of a spatially explicit GIS-based predictive epidemiological model based on suitable environmental factors. We examined eleven commonly mapped environmental factors using both ordinary least squares regression (OLS) and geographically weighted regression (GWR). The GWR model was utilized to ascertain the impact of environmental factors on WNV risk patterns without the confounding effects of spatial non-stationarity that exist between place and health. It identifies the important underlying environmental factors related to suitable mosquito habitat conditions to make meaningful and spatially explicit predictions. Our model represents a multi-criteria decision analysis approach to create disease risk maps under data sparse situations. The best fitting model with an adjusted R2 of 0.71 revealed a strong association between WNV infection risk and a subset of environmental risk factors including road density, stream density, and land surface temperature. This research also postulates that understanding the underlying place characteristics and population composition for the occurrence of WNV infection is important for mitigating future outbreaks. While many spatial and aspatial models have attempted to predict the risk of WNV transmission, efforts to link these factors within a GIS framework are limited. One of the major challenges for such integration is the high dimensionality and large volumes typically associated with such models and data. This research uses a spatially explicit, multivariate geovisualization framework to integrate an environmental model of mosquito habitat with human risk factors derived from socio-economic and demographic variables. Our results show that such an integrated approach facilitates the exploratory analysis of complex data and supports reasoning about the underlying spatial ...
Date: December 2015
Creator: Kala, Abhishek K.
Partner: UNT Libraries

Photo-induced Toxicity of Deepwater Horizon Spill Oil to Four Native Gulf of Mexico Species

Description: The 2010 Deepwater Horizon oil spill resulted in the accidental release of millions of barrels of crude oil into the Gulf of Mexico (GoM). Photo-induced toxicity following co-exposure to ultraviolet (UV) radiation is one mechanism by which polycyclic aromatic hydrocarbons (PAHs) from oil spills may exert toxicity. Blue crab (Callinectes sapidus) are an important commercial and ecological resource in the Gulf of Mexico and their largely transparent larvae may make them sensitive to PAH photo-induced toxicity. Mahi-mahi (Coryphaena hippurus), an important fishery resource, have positively buoyant, transparent eggs. These characteristics may result in mahi-mahi embryos being at particular risk from photo-induced toxicity. Red drum (Sciaenops ocellatus) and speckled seatrout (Cynoscion nebulosus) are both important fishery resources in the GoM. They spawn near-shore and produce positively buoyant embryos that hatch into larvae in about 24 h. The goal of this body of work was to determine whether exposure to UV as natural sunlight enhances the toxicity of crude oil to early lifestage GoM species. Larval and embryonic organisms were exposed to several dilutions of water accommodated fractions (WAF) from several different oils collected in the field under chain of custody during the 2010 spill and two to three gradations of natural sunlight in a factorial design. Here, we report that co-exposure to natural sunlight and oil significantly reduced larval survival and embryo hatch compared to exposure to oil alone.
Date: December 2015
Creator: Alloy, Matthew Michael
Partner: UNT Libraries

Photoinduced Toxicity in Early Lifestage Fiddler Crab (Uca longisignalis) Following Exposure to Deepwater Horizon Spill Oil

Description: The 2010 Deepwater Horizon (DWH) oil spill resulted in a large release of polycyclic aromatic hydrocarbons (PAH) into the Gulf of Mexico. PAH can interact with ultraviolet radiation (UV) resulting in increased toxicity, particularly to early lifestage organisms. The goal of this research was to determine the sensitivity of fiddler crab larvae (Uca longisignalis) to photo-induced toxicity following exposure to Deepwater Horizon spill oil in support of the DWH Natural Resource Damage Assessment. Five replicate dishes each containing 20 larvae, were exposed to one of three UV treatments (10%, 50%, and 100% ambient natural sunlight) and one of five dilutions of water accommodated fractions of two naturally weathered source oils. A dose dependent effect of PAH and UV on larval mortality was observed. Mortality was markedly higher in PAH treatments that included co-exposure to more intense UV light. PAH treatments under low intensity sunlight had relatively high survival. These data demonstrate the importance of considering combined effects of non-chemical (i.e. UV exposure) and chemical stressors and the potential for photo-induced effects after exposure to PAH following the Deepwater Horizon spill.
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Date: December 2015
Creator: Taylor, Leigh M.
Partner: UNT Libraries

Analysis of Students' Knowledge, Perceptions, and Interest in Engineering Post Teacher Participation in a National Science Foundation (NSF) Research Experience for Teachers (RET) Professional Development

Description: This study examined the impact of the National Science Foundation's Research Experience for Teachers (RET) in engineering at University of North Texas on students after their teachers' participation in the program. Students were evaluated in terms of self-efficacy, knowledge of engineering, perceptions of engineering, and interest in engineering. A 22-item Likert pre/post survey was used for analysis, and participants included 589 students from six high schools, one middle school, and one magnet school. Paired surveys were analyzed to determine if there was a statistically significant difference in attitudes and knowledge after teachers implemented lessons from their time at the RET. Surveys were also analyzed to determine if there was a statistically significant difference in student response based on gender or student school type. Results showed no statistically significant difference in the self-efficacy of students, however there was a statistically significant difference in knowledge, perceptions, and interest in engineering. In addition, there was a statistically significant difference between genders on an isolated question, and seven out of the 22 Likert questions showed a statistically significant difference between student school types.
Date: December 2016
Creator: Reeder, Christina
Partner: UNT Libraries

Hepatotoxicity of Mercury to Fish

Description: Tissue samples from spotted gar (Lepisosteus oculatus) and largemouth bass (Micropterus salmoides) were collected from Caddo Lake. Gar and bass livers were subjected to histological investigation and color analysis. Liver color (as abs at 400 nm) was significantly correlated with total mercury in the liver (r2 = 0.57, p = 0.02) and muscle (r2 = 0.58, p = 0.01) of gar. Evidence of liver damage as lipofuscin and discoloration was found in both species but only correlated with liver mercury concentration in spotted gar. Inorganic mercury was the predominant form in gar livers. In order to determine the role of mercury speciation in fish liver damage, a laboratory feeding study was employed. Zebrafish (Danio rerio) were fed either a control (0.12 ± 0.002 µg Hg.g-1 dry wt), inorganic mercury (5.03 ± 0.309 µg Hg.g-1 dry wt), or methylmercury (4.11 ± 0.146 µg Hg.g-1 dry wt) diet. After 78 days of feeding, total mercury was highest in the carcass of zebrafish fed methylmercury (12.49 ± 0.369 µg Hg.g-1 dry wt), intermediate in those fed inorganic mercury (1.09 ± 0.117 µg Hg.g-1 dry wt), and lowest in fish fed the control diet (0.48 ± 0.038 µg Hg.g-1 dry wt). Total mercury was highest in the viscera of methylmercury fed zebrafish (11.6 ± 1.86 µg Hg.g-1 dry wt), intermediate in those fed inorganic diets (4.3 ± 1.08 µg Hg.g-1 dry wt), and lowest in the control fish (below limit of detection). Total mercury was negatively associated with fish length and weight in methylmercury fed fish. Condition factor was not associated with total mercury and might not be the best measure of fitness for these fish. No liver pathologies were observed in zebrafish from any treatment.
Date: August 2010
Creator: Barst, Benjamin Daniel
Partner: UNT Libraries

Ultraviolet Radiation Tolerance in High Elevation Copepods from the Rocky Mountains of Colorado, USA

Description: Copepods in high elevation lakes and ponds in Colorado are exposed to significant levels of ultraviolet radiation (UV), necessitating development of UV avoidance behavior and photoprotective physiological adaptations. The copepods are brightly pigmented due to accumulation of astaxanthin, a carotenoid which has photoprotective and antioxidant properties. Astaxanthin interacts with a crustacyanin-like protein, shifting its absorbance from 473 nm (hydrophobic free form, appears red) to 632 nm (protein-bound complex, appears blue). In six sites in Colorado, habitat-specific coloration patterns related to carotenoprotein complex have been observed. The objective of this study was to determine whether pigment accumulation or carotenoprotein expression has a greater effect on resistance to UV exposure. For each site, copepod tolerance to UV was assessed by survivorship during UV exposure trials. Average UV exposure was determined for each habitat. Astaxanthin profiles were generated for copepods in each site. Ability to withstand UV exposure during exposure trials was significantly different between color morphs (p < 0.0001). Red copepods were found to tolerate 2-fold greater levels of UVB than blue or mixed copepods. Additionally, red copepods have much higher levels of total astaxanthin than blue or mixed copepods (p < 0.0001) and receive a higher daily UV dose (p < 0.0003). Diaptomid carotenoprotein sequence is not homologous with that of other crustaceans in which crustacyanin has been characterized which prevented quantification of carotenoprotein transcript expression. Overall, diaptomid color morph may be an important indicator of UV conditions in high elevation lentic ecosystems.
Date: December 2011
Creator: Hudelson, Karista
Partner: UNT Libraries

Bioconcentration of Triclosan, Methyl-Triclosan, and Triclocarban in the Plants and Sediments of a Constructed Wetland

Description: Triclosan and triclocarban are antimicrobial compounds added to a variety of consumer products that are commonly detected in waste water effluent. The focus of this study was to determine whether the bioconcentration of these compounds in wetland plants and sediments exhibited species specific and site specific differences by collecting field samples from a constructed wetland in Denton, Texas. The study showed that species-specific differences in bioconcentration exist for triclosan and triclocarban. Site-specific differences in bioconcentration were observed for triclosan and triclocarban in roots tissues and sediments. These results suggest that species selection is important for optimizing the removal of triclosan and triclocarban in constructed wetlands and raises concerns about the long term exposure of wetland ecosystems to these compounds.
Date: August 2011
Creator: Zarate, Frederick M., Jr.
Partner: UNT Libraries

Soil and Forest Variation by Topography and Succession Stages in the Greenbelt Corridor, Floodplain of the Elm Fork of the Trinity River, North Texas.

Description: The Greenbelt Corridor (GBC), located in a floodplain of the Elm Fork of the Trinity River, contains patches of bottomland forest and serves as part of Lake Lewisville’s flood control backwaters. This study examines forest structure and composition in relation to topographic position and forest stage in the GBC. Thirty two plots were surveyed within various stage classes, topographic positions, and USDA soil types. Trees were identified and measured for height and DBH. Density, basal area, and importance value for each of species was calculated. Soil and vegetation were analyzed using ANOVA, Principal Component Analysis, Canonical Correlation, Canonical Correspondence Analysis and Cluster Analysis. Tests confirmed that calcium carbonate and pH show significant differences with topographic positions but not with forest stage. Potassium shows no significant difference with soil texture class. Sand shows a strong negative correlation with moisture, organic matter, organic carbon and negative correlation with calcium carbonate and potassium. Silt shows positive correlation with moisture, organic matter, organic carbon, and calcium carbonate. Clay shows strong positive correlation with moisture, organic matter and organic carbon but negative correlations with pH. Swamp privet is dominant tree types in wetland forest. Sugarberry cedar elm, green ash and American elm are widely distributed species in the study area covering low ridges, flats, and slough. In total, density is significantly different in wetland low forest and late successional stage and basal area is significantly different in early successional stage and late successional stage. Other results show that clay is negatively correlated with American elm but positively correlated with cedar elm. Organic matter and moisture shows a strong positive correlation with cedar elm. Calcium carbonate is associated with green ash and swamp privet, sand is associated with sugarberry and red mulberry, silt and pH with cedar elm and bur oak.
Date: August 2011
Creator: Rijal, Rajan
Partner: UNT Libraries

Effect of Rancher’s Management Philosophy, Grazing Practices, and Personal Characteristics on Sustainability Indices for North Central Texas Rangeland

Description: To assess sustainability of privately owned rangeland, a questionnaire was used to gathered data from ranches in Cooke, Montague, Clay, Wise, Parker, and Jack counties in North Central Texas. Information evaluated included: management philosophy, economics, grazing practices, environmental condition, quality of life, and demographics. Sustainability indices were created based on economic and land health indicator variables meeting a minimum Cronbach‘s alpha coefficient (α = 0.7). Hierarchical regression analysis was used to create models explaining variance in respondents’ indices scores. Five predictors explained 36% of the variance in rangeland economic sustainability index when respondents: 1) recognized management inaction has opportunity costs affecting economic viability; 2) considered forbs a valuable source of forage for wildlife or livestock; 3) believed governmental assistance with brush control was beneficial; 4) were not absentee landowners and did not live in an urban area in Texas, and; 5) valued profit, productivity, tax issues, family issues, neighbor issues or weather issues above that of land health. Additionally, a model identified 5 predictors which explained 30% of the variance for respondents with index scores aligning with greater land health sustainability. Predictors indicated: 1) fencing cost was not an obstacle for increasing livestock distribution; 2) land rest was a component of grazing plans; 3) the Natural Resource Conservation Service was used for management information; 4) fewer acres were covered by dense brush or woodlands, and; 5) management decisions were not influenced by friends. Finally, attempts to create an index and regression analysis explaining social sustainability was abandoned, due to the likely-hood of type one errors. These findings provide a new line of evidence in assessing rangeland sustainability, supporting scientific literature concerning rangeland sustainability based on ranch level indicators. Compared to measuring parameters on small plots, the use of indices allows for studying replicated whole- ranch units using rancher insight. Use ...
Date: December 2011
Creator: Becker, Wayne
Partner: UNT Libraries

Integrating Selective Herbicide and Native Plant Restoration to Control Alternanthera philoxeroides (Alligator Weed)

Description: Exotic invasive aquatic weeds such as alligator weed (Alternanthera philoxeroides) threaten native ecosystems by interfering with native plant communities, disrupting hydrology, and diminishing water quality. Development of new tools to combat invaders is important for the well being of these sensitive areas. Integrated pest management offers managers an approach that combines multiple control methods for better control than any one method used exclusively. In a greenhouse and field study, we tested the effects of selective herbicide application frequency, native competitor plant introduction, and their integration on alligator weed. In the greenhouse study, alligator weed shoot, root, and total biomass were reduced with one herbicide application, and further reduced with two. Alligator weed cumulative stem length and shoot/root ratio was only reduced after two applications. In the greenhouse, introduction of competitors did not affect alligator weed biomass, but did affect shoot/root ratio. The interaction of competitor introduction and herbicide did not significantly influence alligator weed growth in the greenhouse study. In the field, alligator weed cover was reduced after one herbicide application, but not significantly more after a second. Introduction of competitor species had no effect on alligator weed cover, nor did the interaction of competitor species and herbicide application. This study demonstrates that triclopyr amine herbicide can reduce alligator weed biomass and cover, and that two applications are more effective than one. To integrate selective herbicides and native plant introduction successfully for alligator weed control, more research is needed on the influence competition can potentially have on alligator weed growth, and the timing of herbicide application and subsequent introduction of plants.
Date: December 2011
Creator: Adams, Justin
Partner: UNT Libraries

Adaptive Advantages of Carotenoid Pigments in Alpine and Subalpine Copepod Responses to Polycyclic Aromatic Hydrocarbon Induced Phototoxicity

Description: Alpine zooplankton are exposed to a variety of stressors in their natural environment including ultraviolet radiation. Physiological coping mechanisms such as the accumulation of photoprotective compounds provide these zooplankton protection from many of these stressors. Elevated levels of carotenoid compounds such as astaxanthin have been shown to help zooplankton survive longer when exposed to ultraviolet radiation presumably due to the strong antioxidant properties of carotenoid compounds. This antioxidant capacity is important because it may ameliorate natural and anthropogenic stressor-induced oxidative stress. While previous researchers have shown carotenoid compounds impart increased resistance to ultraviolet radiation in populations of zooplankton, little work has focused on the toxicological implications of PAH induced phototoxicity on zooplankton containing high levels of carotenoid compounds. This thesis discusses research studying the role that carotenoid compounds play in reducing PAH induced phototoxicity. By sampling different lakes at elevations ranging from 9,500' to 12,700' in the front range of the Colorado Rocky Mountains, copepod populations containing different levels of carotenoid compounds were obtained. These populations were then challenged with fluoranthene and ultraviolet radiation. Results discussed include differences in survival and levels of lipid peroxidation among populations exhibiting different levels of carotenoid compounds, and the toxicological and ecological implications of these results.
Date: May 2010
Creator: Kovach, Matthew James
Partner: UNT Libraries

Wind Energy-related Wildlife Impacts: Analysis and Potential Implications for Rare, Threatened and Endangered Species of Birds and Bats in Texas

Description: Texas currently maintains the highest installed nameplate capacity and does not require publicly available post-construction monitoring studies that examine the impacts of wind energy production on surrounding fauna. This thesis examines potential wind energy impacts on avian and bat species in Texas through a three-part objective. The first two objectives synthesize literature on variables attractive to species within wind development areas and estimate impacted ranges outside of Texas, based on studies examining wind energy's environmental impacts. The third objective focuses on Texas wind development potential for interaction with rare, threatened and endangered species of birds and bats using GIS analysis with a potential hazard index (PHI) model, which addresses broad-spectrum, high risk variables examined within the first two objectives. Assuming areas with higher wind speeds have potential for wind development, PHI values were calculated for 31 avian and ten bat species, based on an analysis of species range data obtained from the Texas Parks and Wildlife Department and wind data obtained from the National Renewable Energy Laboratory. Results indicate one avian species, Tympanuchus pallidicinctus, is at high risk for wind development interaction on an annual basis, with 20 species of birds and nine species of bats at higher risk during the spring season. This macro-scale approach for identifying high risk species in Texas could be used as a model to apply to other conterminous states' preliminary evaluation of wind energy impacts.
Date: August 2010
Creator: Graham, Tara L.
Partner: UNT Libraries

Evaluation of the Developmental Effects and Bioaccumulation Potential of Triclosan and Triclocarban Using the South African Clawed Frog, Xenopus Laevis

Description: Triclosan (TCS) and triclocarban (TCC) are antimicrobials found in U.S. surface waters. This dissertation assessed the effects of TCS and TCC on early development and investigated their potential to bioaccumulate using Xenopus laevis as a model. The effects of TCS on metamorphosis were also investigated. For 0-week tadpoles, LC50 values for TCS and TCC were 0.87 mg/L and 4.22 mg/L, respectively, and both compounds caused a significant stunting of growth. For 4-week tadpoles, the LC50 values for TCS and TCC were 0.22 mg/L and 0.066 mg/L; and for 8-week tadpoles, the LC50 values were 0.46 mg/L and 0.13 mg/L. Both compounds accumulated in Xenopus. For TCS, wet weight bioaccumulation factors (BAFs) for 0-, 4- and 8-week old tadpoles were 23.6x, 1350x and 143x, respectively. Lipid weight BAFs were 83.5x, 19792x and 8548x. For TCC, wet weight BAFs for 0-, 4- and 8-week old tadpoles were 23.4x, 1156x and 1310x. Lipid weight BAFs were 101x, 8639x and 20942x. For the time-to-metamorphosis study, TCS showed an increase in weight and snout-vent length in all treatments. Exposed tadpoles metamorphosed approximately 10 days sooner than control tadpoles. For the hind limb study, although there was no difference in weight, snout-vent length, or hind limb length, the highest treatment was more developed compared to the control. There were no differences in tail resorption rates between the treatments and controls. At relevant concentrations, neither TCS nor TCC were lethal to Xenopus prior to metamorphosis. Exposure to relatively high doses of both compounds resulted in stunted growth, which would most likely not be evident at lower concentrations. TCS and TCC accumulated in Xenopus, indicating that the compound has the potential to bioaccumulate through trophic levels. Although TCS may increase the rate of metamorphosis in terms of developmental stage, it did not disrupt thyroid function and metamorphosis in ...
Date: December 2010
Creator: King, Marie Kumsher
Partner: UNT Libraries

Habitat Fragmentation by Land-Use Change: One-Horned Rhinoceros in Nepal and Red-Cockaded Woodpecker in Texas

Description: This research focuses on the spatial analysis of the habitat of two vulnerable species, the one-horn rhinoceros in the grasslands of southern Nepal, and the red-cockaded woodpecker in the Piney woods of southeast Texas, in the USA. A study sites relevant for biodiversity conservation was selected in each country: Chitwan National Park in Nepal, and areas near the Big Thicket National Preserve in Texas. Land-use differs in the two study areas: the first is still undergoing agrarian development while the second is in a technological phase and undergoing urbanization processes. Satellite remote sensing images were used to derive land-cover maps by supervised classification. These maps were then processed by Geographic Information Systems methods to apply habitat models based on basic resources (food and cover) and obtain habitat suitability maps. Several landscape metrics were computed to quantify the habitat characteristics especially the composition and configuration of suitable habitat patches. Sensitivity analyses were performed as the nominal values of some of the model parameters were arbitrary. Development potential probability models were used to hypothesize changes in land-use of the second study site. Various scenarios were employed to examine the impact of development on the habitat of red-cockaded woodpecker. The method derived in this study would prove beneficial to guide management and conservation of wildlife habitats.
Date: December 2010
Creator: Thapa, Vivek
Partner: UNT Libraries

Role of N-Acylethanolamines in Plant Defense Responses: Modulation by Pathogens and Commercial Antimicrobial Stressors

Description: N-acyl ethanolamines (NAEs) are a class of lipids recently recognized as signaling molecules which are controlled, in part, by their degradation by fatty acid amide hydrolase (FAAH). On the basis of previous studies indicating increased NAE levels in a tobacco cell suspension-xylanase elicitor exposure system and the availability of FAAH mutants, overexpressor and knockout (OE and KO) genotypes in Arabidopsis thaliana, further roles of NAEs in A. thaliana plant defense was investigated. The commonly occurring urban antimicrobial contaminant triclosan (TCS) has been shown to suppress lipid signaling associated with plant defense responses. Thus, a second objective of this study was to determine if TCS exposure specifically interferes with NAE levels. No changes in steady state NAE profiles in A. thaliana-Pseudomonas syringae pv. syringae and A. thaliana-flagellin (bacterial peptide, flg22) challenge systems were seen despite evidence that defense responses were activated in these systems. There was a significant drop in enoyl-ACP reductase (ENR) enzyme activity, which catalyzes the last step in the fatty acid biosynthesis pathway in plants, on exposure of the seedlings to TCS at 10 ppm for 24 h and decreased reactive oxygen species (ROS) production due to flg22 in long term exposure of 0.1 ppm and short term exposure of 5 ppm. However, these responses were not accompanied by significant changes in steady state NAE profiles.
Date: August 2010
Creator: Vadapalli, Vatsala
Partner: UNT Libraries