Browsing by Subject "invasive species"
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Item Amphibian and Reptile Trade in Texas: Current Status and Trends(2010-10-12) Prestridge, Heather L.The non-game wildlife trade poses a risk to our natural landscape, natural heritage, economy, and security. Specifically, the trade in non-game reptiles and amphibians exploits native populations, and is likely not sustainable for many species. Exotic amphibian and reptile species pose risk of invasion and directly or indirectly alter the native landscape. The extent of non-game amphibian and reptile trade is not fully understood and is poorly documented. To quantitatively describe the trade in Texas, I solicited data from the United States Fish and Wildlife Service's (USFWS) Law Enforcement Management Information System (LEMIS) and Texas Parks and Wildlife Department's (TPWD) non-game dealer permits. I surveyed amphibian and reptile pet owners, breeders, Internet sites, pet shops, and meat and seafood establishments by visits, electronic surveys, and observations. The trade in exotic species of amphibians and reptiles in the state of Texas was found to be popular in two ways; the importation of wildlife products and sale of live specimens for pets. Persisting in the pet trade were species known to be exotic, a problem made worse by lack of regulations governing the import, export, and keeping of exotic species. Trade in wild collected native species was primarily for export to foreign countries. Collection of turtles from the wild in Texas was heavy until 2008, when TPWD restricted collection to private waters. Collection of other species from the wild was minimal, with the exception of the Western Diamond-backed Rattlsnake (Crotalus atrox) for rattlesnake roundups. Native species were found to exist in the pet trade, but primarily as genetic color variants that do not occur in the wild, an indication that captive breeding may be relieving pressures on wild caught specimens. Minor changes in reporting requirements and permitting systems at the state and federal level would improve the management of exotic and native amphibians and reptiles that persist in the trade. Changes that include standardized taxonomic reporting requirements at state and federal level, streamlined permitting system for individuals wishing to collect from the wild in Texas, bag limits and seasons for wild collection, increased reporting requirements for owners of exotics, and enforcement of reporting errors would aid in management of exotic and native amphibians and reptiles in the trade.Item Bacteria in Ballast Water: The Shipping Industry's Contributions to the Transport and Distribution of Microbial Species in Texas(2010-10-12) Neyland, Elizabeth B.The transportation of organisms in the ballast water of cargo ships has been recognized as a source of invasive species despite current control measures. Pathogenic bacteria in the ballast tank have been studied but the total diversity of the ballast tank bacterial community has not been examined. This study is the first to characterize the total bacterial community within a ballast tank by constructing a clone library from a ballast water sample from a cargo ship in the Port of Houston, amplified ribosomal rDNA restriction analysis (ARDRA) and phylogenetic analysis. Bacterial communities in Texas ports and bays were also examined using denaturing gradient gel electrophoresis (DGGE), looking at both temporal and spatial variations for effects of deballasting activity. This ballast tank bacterial community had a high level of diversity (95%) with the clone library only representing 40% of the total community of the tank. Most probable originating habitats of the ballast bacteria were: marine pelagic (40%), estuarine (37%), coastal (6%), freshwater (3%) and other (14%), even though this ballast tank was exchanged with pelagic water. Predominate groups were alpha- and gammaproteobacteria, a few betaproteobacteria and bacteriodetes, and one each of verrucomicrobia, planctomycetes and actinobacteria, but no pathogens were detected. The data reveals a ballast tank that consists of half marine-pelagic, half port bacteria, revealing a low efficacy of exchange control methods and potentially invasive bacteria. The bacterial communities of five ships that exchanged ballast water in the Pacific Ocean shared on average 50% similarity. Two ships that exchanged ballast water in temperate latitudes were more similar than three other ships that exchanged in tropical latitudes, showing a correlation between location of exchange and community similarity. The bacterial communities of the Ports of Houston and Galveston exhibit stable, seasonal successions over one year. The port and bay systems of Texas exhibited spatial variations in bacterial communities related to salinity levels. Both experiments did not show evidence of community disruption by deballasting activities. This study shows that ballast water is a viable vector for invasive bacterial transport, although impact on Texas estuarine systems seems minimal.Item Dynamics of water use and responses to herbivory in the invasive reed, Arundo donax (L.)(2010-07-14) Watts, David A.The first objective of this study was to investigate the role of an invasive grass species, Arundo donax (L.), on the hydrologic cycle. At a site on the Rio Grande in South Texas, we measured the gas exchange of carbon dioxide and water vapor at the leaf scale and structural characteristics, such as leaf area and shoot density, at the stand scale. In order to assess the effect of water availability, this study was conducted along transects perpendicular to the edge of the river along a potential moisture gradient. The second objective was to quantify the effect of two herbivores, an armored scale, Rhizaspidiotus donacis (Leonardi), and a stem-galling wasp, Tetramesa romana (Walker),on the photosynthetic and transpiration rates of A. donax. Leaf gas exchange measurements were made to determine the direction and magnitude of the effect on physiological processes and by what mechanisms any effects arose. Stands of A. donax used approximately 9.1 ? 1.1 mm of water per day. This rate of water use was at the high end of the spectrum for plants. The major controls on stand scale transpiration were evaporative demand, leaf area index, and water availability. During two summer seasons, stand scale transpiration varied greatly, following the pattern of variability in precipitation, suggesting that recent rainfall constituted a significant proportion of the water taken up by this species. Herbivory by a stem-galling wasp and a sap-feeding scale, both separately and together, reduced the rates of leaf scale physiological processes in A. donax. The efficacy of the wasp was density dependent, and this herbivore reduced the carboxylation rate of Rubisco. The effect of the scale took approximately five months to manifest, which coincided with generation time. Scale reduced photosynthesis by decreasing the maximum rate of electron transport. When the two insects were both present, the effect of their herbivory seemed to be additive. These results will assist the responsible management agencies in evaluating the propriety of using one or both of the insect herbivores as biological control agents.Item Ecohydrological Controls and Effects of Rhizome Integration on the Performance of Arundo donax in a Rio Grande Riparian Zone(2012-10-19) Kui, LiThis study focused on an invasive riparian reed grass, Arundo donax L., a clonal plant of the family Poaceae that is widely distributed in North America. Water availability, including water taken up from the roots locally or transported from the neighboring ramets, may affect the performance of A. donax in riparian zones. The first objective was to find out how moisture gradients affected the performance of A. donax in riparian zones. I measured leaf photosynthetic rate, leaf ?13C ratio, and plant growth-related parameters across two summer growing seasons at four transects perpendicular to the water course on the Rio Grande in South Texas. The second objective was to find out whether physiological integration existed in A. donax and how resource sharing, if any, affected plant growth. A rhizome severing experiment was conducted on five paired plots to compare growth-related parameters between plots with rhizomes severed and intact at 3, 7, and 11 weeks after treatment. Heavy water (? 2H ~1800?) was applied on three 1-m2 area over 3 successive days and rhizome samples were collected beyond the watering zone after 5, 24, and 48 hours of last watering. At short-term scales, A. donax performance was adversely affected by both drought and inundated conditions; over longer time scales, plant performance decreased as water availability declined in general, but biomass and stem density were similar across moisture gradients. I also found evidence of physiological integration in A. donax. Water was transported through interconnected rhizomes at least 3.5 m; transport distances averaged 1.67 m. Rhizome severing stimulated higher ramet production initially but over longer periods produced shorter thinner stems with lower flood tolerance. However, after 11 weeks of re-growth, plot-level biomass was similar between plots with severed and intact rhizomes. These results suggest that performance of A. donax is affected by water availability in riparian zones; however, clonal plant plasticity, water use efficiency, and clonal integration ameliorate impacts of water stress on the performance of A. donax. Such traits enhance its resource use, which could potentially increase competitive ability rate of establishment, and extent of this invasive species in heterogeneous riparian environments.Item Effects of Local Adaptation of Invasion Success: A Case Study of Rhithropanopeus harrisii(2013-06-04) Boyle, Terrence MichaelA major trend in invasion biology is the development of models to accurately predict and define invasive species and the stages of their invasions. These models focus on a given species with an assumed set of traits. By doing so, they fail to consider the potential for differential success among different source populations. This study looked at the inland invasion of Rhithropanopeus harrisii in the context of a current invasion model. This species has been introduced worldwide, but has only invaded freshwater reservoirs within the state of Texas (United States) indicating a potential difference amongst source populations. Previous studies indicate that this species should not be capable of invading inland reservoirs due to physiological constraints in the larvae. A more recent study gives evidence to the contrary. To investigate whether the inland populations are in fact successfully established, I attempted to answer the following questions: Can inland populations successfully reproduce in the inland reservoirs and rivers? If so, what factors in the native environment could have led to the evolution of this ability? What are the impacts of this species in the inland reservoirs and what is its potential spread? I combined a larval developmental study, conspecific and heterospecific crab competition trials, field collections, gut content analysis, shelter competition trials with crayfish, and larval and adult dispersal study to answer these questions. I showed that Rhithropanopeus harrisii is established in the inland reservoirs and capable of spreading. I demonstrated that in the native populations along the Gulf coast of the United States, this species is the least aggressive and is therefore likely excluded into lower salinity waters during reproductive periods. This likely led to a lowered salinity tolerance in the larval stages, which predispose these populations to successful introductions in inland freshwater bodies. I showed that the crabs are capable of outcompeting juvenile crayfish for shelter at high densities and therefore warrant management in order to reduce their effect. This study indicates a need for the invasion models to take the source population into account in order to ensure effective and prudent management strategies.Item Select Economic Implications for the Biological Control of Arundo donax along the Rio Grande(2010-10-12) Seawright, Emily KayeArundo donax, or giant reed, is a large, bamboo-like plant native to Spain that has invaded several thousand acres of the Rio Grande riparian in Texas. The plant grows to 18-24 feet, consuming large quantities of water per acre per year. With concern of increased water demands in the Texas Lower Rio Grande Valley region, the United States Department of Agriculture-Agricultural Research Service (USDA)ARS) is investigating four herbivorous insects as potential biological control agents for Arundo donax to facilitate increased water supply. This study examines select economic implications for agricultural water users in the United States of applying these biological control agents along the Rio Grande. The research includes (a) estimating the value of the water saved due to the reduction of Arundo donax, (b) a benefit-cost analysis, (c) regional economic impact analysis, and (d) an estimate of the per-unit cost of water saved over a 50-year planning horizon (2009 through 2058). The model ArundoEcon is used to perform a deterministic analyses using low- and high-marginal-composite acre values. Regional results indicate present values of farmlevel benefits ranging from $97.80 to $159.87 million. Benefit-cost ratios are calculated with normalized prices and range from 4.38 to 8.81. Sensitivity analyses provide a robust set of results for Arundo water use, replacement species water use, Arundo expansion rate after control, value of water, and the cost of the program. The pre-production processes and farm-gate economic impact analysis is estimated using multipliers from the IMPLAN model. Regional results reveal a range of $8.90 to $17.94 million annually in economic output and 197 to 351 new jobs for the year 2025. Further results show the cost per acre-foot of water saved is $44.08. This amount is comparable to other projects designed to conserve water in the region. The USDA)ARS, Weslaco, Texas Arundo donax biological control project realizes positive results for the benefit-cost ratios, economic impact analyses, and competitive results for the per-unit cost of saving water. These positive results indicate this project will have positive economic implications for the U.S. and the Texas Lower Rio Grande Valley.Item Ticks and Tick-Borne Pathogens Associated with Feral Swine in Edwards Plateau and Gulf Prairies and Marshes Ecoregions of Texas(2012-07-16) Sanders, David M.Feral swine (Sus scrofa domesticus) are spreading across North America at an alarming rate. Four Canadian provinces and 39 states within the continental United States now report standing populations of feral pigs. Estimates place the number of feral hogs in Texas >2M, accounting for more than half of the United States population. It is known that feral swine impact local ecology following establishment, with regard to shifts in local flora and fauna. The overall objective of this research was to investigate the role of feral swine in tick-borne pathogen transmission in Texas. The underpinning objectives were to establish host records for tick species parasitizing feral swine, determine the species assemblages associated with feral swine among different ecoregions of Texas, determine by immunoassay to which tick-borne bacteria feral pigs were being exposed, and detect the DNA of tick-borne bacteria by polymerase chain reaction assay in the event of poor or early immune response by the host. Feral pigs (N=432) were harvested from June 2008 to June 2010 using box and corral traps and by aerial gunning. Seven species of ticks, Amblyomma americanum, A. cajennense, A. maculatum, Dermacentor albipictus, D. halli, and D. variabilis; and Ixodes scapularis, were collected. Immature stages of A. cajennense and A. americanum were collected as well. All classes of feral pigs, gender by age, were infested with ticks. Serum was collected through a multi-organizational effort from 2006 to 2010 and tested by ELISA for previous exposure to tick-borne pathogens in the genera Rickettsia and Ehrlichia (N=888) and Borrelia (N=849). Prevalence percentages by immunoassay were 27.59 percent, 13.18 percent and 2.12 percent for Rickettsia, Ehrlichia, and Borrelia, respectively. Samples positive by ELISA for exposure to Borrelia were further screened by Western Blot for exposure to Borrelia turicatae. The results were equivocal in most cases. Blood samples (N=233) were collected from 2008 to 2010 and analyzed by polymerase chain reaction for the detection of the DNA of these same three genera of bacteria. Two of the samples were positive by PCR for the presence of Borrelia DNA. Texas feral swine are serving as hosts for at least seven species of ticks and are interacting with tick-borne pathogen transmissions cycles in Texas.