Theses and Dissertations, Capstones, and Directed Research
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Electronic theses and dissertations, and graduate and undergraduate Capstones and Directed Research.
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Browsing Theses and Dissertations, Capstones, and Directed Research by Department "Biology"
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Item A comparative analysis of plant species distribution and growth response to edaphic features between the San Saba River and a tributary(2013-05) Henson, Jeremy D.; Lemke, David E.Riparian corridors are often a mosaic of vegetative communities that serve as interfaces between terrestrial and aquatic systems and, consequently, span multiple environmental gradients. As such, an interesting question is whether the interconnection of streams and tributaries within a drainage basin facilitates homogeneous community structure and development, or if these systems host distinctly different floras as a result of differing physiognomy and disturbance cycles. In relation to the size of the state, relatively few comprehensive qualitative or quantitative surveys of natural plant resources within managed areas of Texas have been conducted. As a result, quantitative data on vegetation are insufficient to support fine scale plant community classification for most of the natural regions in Texas. The objectives of this research were to 1) conduct a comprehensive floristic survey of the study site to identify, collect, and preserve specimens of each plant species located on-site and 2) conduct a comparative analysis to evaluate patterns of plant species richness and distribution in relation to edaphic characteristics between three riparian communities with different hydrologic regimes. Results show that, although multiple factors influence a particular ecological dynamic, only certain factors have a greater degree of importance in the development of plant communities. The most important factor in plant species distribution and richness at the study site appears to be moisture availability, with secondary effects of nutrient availability from flood deposits, as well as physical impacts from flood disturbance.Item A Comparative Primary Productivity Study of Three Ponds Consisting of Different Primary Producers(1968-08) Anderson, Bobby T.; Hannan, Herbert H.; Whiteside, Bobby Gene; Martine, FloydNo abstract prepared.Item A Comparative Study of the Distribution and Activities of the Ornithine Cycle Enzymes in Five Gastropods(1969-01) Boonkoom, Viroj; Horne, Francis R.; Green, Don C.; Willms, Charles R.No abstract prepared.Item A Comparative Study of the Hydracarina (Acarina) in Three Permanent Ponds(1969-05) Barker, Ernest David; Young, Willard C.; Hannan, Hebert H.; Yager, Billy J.No abstract prepared.Item A Comparative Study of Two Populations of Psephenus Texanus: (Coleoptera, Psephenidae) in the San Marcos and Comal Rivers(1978-08) Carrola, Harry Lee; Tuff, Donald W.; Young, Willard C.; Whiteside, Bobby G.No abstract prepared.Item A comparison of constitutive and induced immune response in coral colonies of variable symbiont densities(2022-12) Changsut, Isabella; Fuess, Lauren E.; McLean, Robert J.C.; Rodriguez, DavidScleractinian corals form the basis of diverse coral reef ecosystems. However, corals are in swift decline globally, in part due to rising disease prevalence. Most corals are dependent on symbiotic interactions with single-celled algae (family Symbiodiniaceae) to meet their nutritional needs. Preliminary evidence suggests that suppression of host immunity may be essential to this relationship. To explore potential immunological consequences of symbiotic relationships in corals, we investigated constitutive and induced immune activity in the facultatively symbiotic coral, Astrangia poculata. Brown (high symbiont density) and white (low symbiont density) colonies of A. poculata were collected from Rhode Island. First, we compared constitutive immune phenotypes between these two groups. Symbiont density was strongly correlated to several of these immune phenotypes; catalase activity and melanin were significantly positively correlated to symbiont density. Next, we investigated potential variation in induced immune response between the two groups. Colonies of A. poculata with variable symbiont densities were exposed to a pathogenic challenge. We then measured differences in constitutive and induced immunity using transcriptomic approaches. Preliminary results indicate significant differences in response to immune challenge as a result of variable symbiont density. Our results highlight the complex nature of symbiosis-immune interplay in cnidarians and emphasize the need for nuanced approaches when considering symbiosis.Item A Comparison of Eradication Techniques for a Nonindigenous Emergent Plant Species (Colocasia esculenta)(2006-12) Atkins, Eric O.; Williamson, Paula S.Colocasia esculenta (L.) Schott is a nonindiginous emergent plant species that was introduced to Spring Lake and the upper San Marcos River (Hays County, Texas) ecosystem in the 1900s. This species forms dense stands along the river and has demonstrated the ability to dominate many areas previously inhabited by native vegetation. Texas Parks and Wildlife Department has listed C. esculenta as an exotic species needing management consideration. In this study, four eradication techniques were applied to C. esculenta growing along the banks of Spring Lake and the San Marcos River at five week intervals from November 2004 to November 2005. The four techniques were manual removal, application of the herbicide glyphosate, mechanical cutting with hand shears, and a combination of mechanical cutting followed by application of glyphosate to the cut petiole. Data collected and analyzed included leaf cover of C. esculenta, number of treatment applications required to achieve eradication, amount of time required to apply each eradication technique, and percent cover of other plant species growing in each quadrat. The effectiveness of each eradication technique was based on four criteria: the extent of decrease in C. esculenta leaf cover, the number of treatment applications required to achieve eradication, the amount of time for the application of the technique, and the extent of growth by other plant species. After one year C. esculenta leaf cover following both manual removal and herbicide application was significantly less than the leaf cover of the mechanical cutting technique and the control (F4j2s - 34.704, p = <0.001). Manual removal required significantly fewer treatment applications to eradicate C. esculenta than the mechanical cutting and the combination mechanical cut/herbicide techniques (F4,25 = 16.671, p = <0.001) while the herbicide application required significantly fewer applications than the mechanical cutting technique (F4,25 = 16.671, p = <0.001). Neither the mechanical cutting nor the combination mechanical cut/herbicide technique resulted in eradication of C. esculenta. The manual removal technique required significantly less application time than both the mechanical cutting technique and the combination mechanical cut/herbicide technique (F4,25 = 17.364, p = <0.001). The herbicide application resulted in a significantly greater total percent plant cover, excluding C. esculenta, than the control (F4s 25 = 3.192, p = 0.03). Based on the four criteria manual removal and herbicide application techniques are the only techniques effective in eradicating C. esculenta.Item A Comparison of Fungal and Bacterial Activity on Decomposing Leaves of Colocasia Esculenta (Araceae)(1998-08) Cleveland, William A.; Koehn, Robert D.; Lemke, David E.; Williamson, Paula S.Decomposition of submerged and free standing terrestrial leaves of the aquatic macrophyte, Colocasia esculenta (Elephant Ear) by fungi and bacteria was studied. Leaves were cut from their petioles and submerged in waters of Spring Lake, San Marcos, Texas. Fungal activity was measured indirectly by the ergosterol method using a high performance liquid chromatograph. Bacterial activity was obtained using DAPI epifluorescent stain. Submerged leaves decomposed in 16 days. Bacterial concentration steadily increased over the 16 day period. No ergosterol was detected in submerged leaves indicating decomposition was due to bacterial activity. Free standing leaf decomposition occurred over a period of 40 days. Ergosterol content within the leaf plugs increased from 0 µg ergosterol/ g dry leaf mass to 3681.58 µg ergosterol/ g dry leaf mass whereas bacteria were found to be-at a minimal level indicating that fungi were most actively involved in the decomposition of the terrestrial leaves. A total of ten different fungal species were identified from the terrestrial leaf plugs.Item A consideration into ways biology-based student organizations facilitate participation in STEM(2019-08) Nolen, Zachary Lee; Daniel, Kristy; Bucklin, Carrie; Castro-Arellano, Ivan; Close, Eleanor; Williamson, PaulaStudent involvement on their campus is a vital part of their experience in higher education. A lack of involvement and engagement can lead to a decreased sense of belonging on campus and in their chosen field of study. Researchers speculate that one reason students leave STEM is because students have not developed a strong perceived attachment to the field of science. One way that students may build this perceived attachment to science is through increasing their engagement and participation in science-based activities. By participating in science-based social organizations, students are exposed to new experiences they would not normally have during their coursework. The purpose of my study was to investigate how biology-based student organizations functioned as affinity groups and how these groups influenced individuals’ perceived cohesion to science. I followed three biology-based student organizations, biological honor society, microbiology club, and wildlife club, over the course of one academic year to identify the extent they exhibited the characteristics of affinity groups. After collecting and analyzing data from field observations, I found that all three groups exhibited the criteria of affinity groups to various degrees. Through analyzing student responses to an open-ended questionnaire, I was able to uncover the motivations students had for joining their respective student organizations and what benefits they reported receiving from their participation. I found three major overarching themes for what motivated students to join their respective student organization: they liked the content the organization was based on, to have some form of social outlet, or the reputation of the organization drew them into the organization. Students reported a wide range of benefits they received from their participation in these organizations. I grouped these benefits into five overarching themes: Networking, Professional Development, Learning Opportunities, Community Involvement, and Prestige. I found that there was some overlap between students’ motivations for joining their student organization and what benefit they received from their participation. With this overlap, I speculate that a feedback loop exists where students join an organization for a specific reason that guides what events they choose to participate in which then leads into the benefit they receive from their participation. Now that we better understand how these organizations function, what motivates students to join content-based student organizations, and what they are getting from their experiences, we can further promote these groups to new students. By joining a content-based student organization, students will be better able to find their place in science through networking with others in their field and honing and developing skills that they can take into the workforce, ultimately making them more competitive on the job market.Item A GIS Model for Identifying Potential Breeding Habitat for the Houston Toad (Bufo houstonensis)(2008-08) Buzo, Daniela; Forstner, Michael R.J.; Green, M. Clay; Fonstad, Mark A.Identification and characterization of suitable habitat is fundamental for modern conservation biology and wildlife management. Threatened and endangered species are excellent candidates for a landscape level approach to habitat suitability predictive models. I used soil type, canopy cover, and distance to water source as environmental variables to predict potential habitat for the endemic and highly endangered amphibian Bufo houstonensis. The accuracy of the models was evaluated by overlaying species occurrence data onto predictive habitat suitability maps. I used a chi-square goodness of fit test to examine whether the observed frequencies of occurrence in each habitat category were different than would be expected if they occurred in the categories relative to their availability. These categories were: High, Medium, Low, Very Low and None. Overall, model evaluation demonstrated that habitat suitability models performed well when predicting species occurrence in High and Medium suitable habitat categories and species absence in Very Low and None categories. This study provides important information for the recovery of Houston Toad. It enables the evaluation of surveys, identifies localities that are not currently occupied but appear to have suitable habitat, and aids in the selection of suitable re-introduction sites.Item A Heat Budget for Canyon Reservoir, A Subtropical Impoundment in Southcentral Texas(2000-12) Bass, David A.; Groeger, AlanAnnual heat budgets were constructed for a subtropical (30°N) reservoir over its 31-year history and used to examine the influence of local climatic variability on hydrological and thermal processes. Heat balances were calculated using both observed and derived hydrological and meteorological data, and some of the heat flux equations were modified to more accurately reflect the local climate. During this study period, surface heat exchange accounted for 67% of the annual heat flux. The magnitude and patterns of surface heat fluxes observed at Canyon Reservoir were intermediate between those of tropical and temperate lakes. The reservoir showed the sinusoidal pattern of heat gain seen in temperate lakes, but the amount of heat flux was more similar to tropical reservoirs. The climate of southcentral Texas is quite variable, and over its history Canyon Reservoir has experienced several major floods and droughts, providing insight into the role advection plays in reservoir heat dynamics. The reservoir acted as a trap for advected heat. The contribution advected heat made to the total heat budget averaged 33%, but varied from < 1% to > 95% depending on the volume of water entering the reservoir and time of year. To further explore the role advection played in Canyon Reservoir’s heat dynamics, data on the three wettest and driest years were compared. Net heat balances were quite different between the two groups of years. In the driest years, the reservoir lost 52 cal cm"2 d"1 more heat than the 31-yr mean, making the reservoir an overall heat source to its environment. During the wettest years, the reservoir gained 19 cal cm"2 d"1 more heat than the 31 -yr annual mean, increasing its role as a heat trap.Item A Key for Identifying Grasses (Paoceae) of the Balcones Canyonlands of Texas by Vegetative Characters(2002-12) Hagenbuch, KarlNo abstract prepared.Item A lamprey gonadotropin-releasing hormone in the bovine brain(2001-05) Warner, Kara E.; Koke, JosephMammalian gonadotropin release from the anterior pituitary is under control of the hypothalamic luteinizing hormone-releasing hormone (LHRH) and a putative analog, follicle stimulating hormone-releasing factor (FSHRF). Analogs of mammalian LHRH and their receptors have been isolated in various animals; of these, the lamprey-gonadotropin-releasing hormone-IH (lampreyGnRH-IH) analog seems the most likely candidate as a possible independent FSHRF in the mammalian system. On the basis of these studies, I hypothesized that lamprey-GhRH-III may be a FSHRF in mammals, and if so, it should be possible to demonstrate the presence of this hormone during bovine brain development. To test this hypothesis, I used immunofluorescence to determine 1) if lamprey-GnRH-in is present in the fetal bovine brain and 2) at what stage during development this hormone is expressed. Additionally, I sought 3) to localize a receptor to which lamprey-GnRH-IH may bind on anterior pituitary cells, and 4) to determine the level of colocalization of GnRH receptor and the downstream effect of this ligand-receptor interaction: FSH. Three trimester ages of brain were studied in order to determine the presence of this gonadotropinreleasing hormone associated with neurons during fetal bovine development The antibody to lamprey-GnRH-in was found bound to neuronal membranes in the diencephalon region of the fetal brain at all ages studied. Additionally, GnRH receptor antibody was found on fetal anterior pituitary cells colocalized with FSH. These results indicate that the lamprey-GnRH-III analog or a closely related peptide is present in the bovine brain, and may be a mammalian FSHRF.Item A Limnological Study of the New Braunfels-Gonzales Stretch of the Guadalupe River(1970-01) Parsons, David StanleyNo abstract prepared.Item A Morphological and Molecular Reassessment of Robergea albicedrae (Ascomycota)(2019-12) Bernardin, Jessica Rae; Lemke, David E; Rodriguez, David; Hahn, DittmarHistorically, ascomycete fungi have been classified based on key morphological characteristics such as spore size and shape, ascus morphology, and biochemical indicators. This approach has resulted in groups of organisms that are microscopically and macroscopically similar, however, in some situations these groupings are not supported by the results of modern phylogenetic studies. Robergea albicedrae is a fungus that grows on the bark and twigs of a single species of tree, the Ashe juniper (Juniperus ashei). First described in 1910, the fungus has been reassigned at the generic and family levels several times over the past century and is now classified in Stictidaceae. The goal of this study was to provide new morphological and molecular data to better understand the life cycle and relationships of the species. Procedures were designed to culture the fungus both in situ and in vitro. Plastic coverslips were placed on the bark of Ashe juniper for 17 months in an attempt to document the stages of the life cycle of the fungus. Samples of Robergea albicedrae were also cultured using a variety of media and plating techniques. Robergea albicedrae, along with a diversity of other fungi, was successfully grown on coverslips and in pure culture. Robergea albicedrae was also sequenced and analyzed at the 18S SSU rDNA and ITS 1 and 2 regions. Analyses of these sequences using Bayesian phylogenetics provided strong support for the placement of Robergea albicedrae in the order Ostropales and the family Stictidaceae of the class Lecanoromycetes.Item A Morphometric Study of Plagioporus sinitsini Mueller (Digenea: Opecoelidae) from the Gallbladder of Three Cyprinid Hosts from the Blanco, San Marcos, and Comal Rivers in Central Texas(1993-12) Mathis, Suzette DeniseNo abstract prepared.Item A non-linear spotlight line transect method for estimating white-tailed deer population densities(2000-05) Pierce, Brian L.; Baccus, John T.; Manning, Richard W.; Simpson, Thomas R.Accurate estimates of population density are a prerequisite for managing exploited white-tailed deer (Odocoileus virginianus) populations. Many state agencies rely upon density estimates obtained from spotlight strip transect surveys to regulate annual harvest Yet, density estimates from the standard spotlight strip transect method are known to be inaccurate in areas of dense vegetation, and alternatives such as the Hahn method, mark-recapture, or aerial strip transects are cost prohibitive for state wide surveys~ The line· transect method is an alternative which has been criticized for inaccuracy of distance estimates and the additional time required to collect perpendicular distance data. Results from a two year study of white-tailed deer in central Texas are presented to demonstrate the utility of a new spotlight line transect sampling method. The method generates accurate perpendicular distance data from non-linear transects using inexpensive GPS, GIS, and laser range finding equipment. The new spotlight line transect method is relatively fast (0.15 ± 0.05 hours/km SD), spatially accurate to within limits of the equipment used (15.2 ± 13.9 m SD), consistently obtains larger sample sizes per transect (> 50% ), and returns more information per sighting (count, composition, and spatial location) than traditional spotlight strip transect sampling method. Results indicate the new spotlight line transect method is less biased than the traditional spotlight strip transect method, more efficient in terms of cost per unit effort (hours/km), and yields spatial data (deer locations) applicable for monitoring habitat use without identification of individuals (Design 1, Thomas and Taylor 1990).Item A Recreational Use Survey of the San Marcos River(1994-05) Bradsby, David D.; Whiteside, Bobby G.; Arsuffi, Tom L.; Longley, GlennNo abstract prepared.Item A spatiotemporal habitat fragmentation analysis for the endangered Houston toad (Bufo houstonensis)(2015-08) Wallace, Derek Michael; Forstner, Michael R. J.; Veech, Joseph A.; Jensen, JenniferNo abstract prepared.Item A Statistically Designed Karst Feature Survey, and Factors Controlling Karst Feature Density and Distribution(2019-12) Martinez, Lorena; Schwartz, Benjamin; Jensen, Jennifer; Swannack, ToddKarst feature inventories provide essential information used to evaluate a site’s degree of hydrogeologic connectivity to local and regional flow systems, as well as its environmental and ecological sensitivity. For developments proposed on the Edwards Aquifer recharge zone, TCEQ rules require a full-coverage karst feature inventory of karst features during a geological assessment. However, visual surveys may be subjective, depending on the experience of the person performing a survey. Considering this, my research focused on whether it is possible to develop an independent method for identifying the most sensitive recharge areas for visual surveys, when time and resources are limited, as well as provide a means for assessing the accuracy of surveys. The question motivating this research is: can relationships be identified between predictor variables and karst feature density that allow estimation of density without physical surveys? A partial, statistically-designed, karst feature survey of the 17 km2 Freeman Center of Texas State University in San Marcos, Texas resulted in 60 documented karst features, including three sinkholes ground-truthed from a GIS-based sinkhole detection method. The survey design used for Freeman was then tested on Camp Bullis, near San Antonio, TX, an area with known karst feature density, revealing that random surveying does not yield representative karst feature density results, as karst features tend to cluster. The entirety of Camp Bullis was analyzed for factors that influence karst feature density. An Ordinary Least Squares model determined that slope, distance to nearest flowline, lithology, and apparent resistivity were significant predictors of karst feature density (R= 0.30; p<0.01). A Geographically Weighted Regression was also used to visualize the nonstationarity of predictor variables (R= 0.81). However, both models resulted in spatial autocorrelation of residuals, indicating model misspecification. Despite concluding that karst features density is difficult to model, these methods offered a more nuanced understanding of factors controlling the distribution of karst features and the significance of these factors on Camp Bullis.