Browsing by Subject "Invasive species"
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Item A Study on Biological Threats to Texas Freshwater Resources(2014-01-15) Neisch, MichaelThis thesis consists of two separate experiments on unique biological threats to Texas freshwater ecosystems. The first experiment sought to understand the interaction between the harmful alga Prymnesium parvum and the cyanobacteria, Anabaena sp. The second experiment sought to determine the effectiveness of triploid grass carp, Ctenopharyngodon idella, as a biological control for two species of invasive macrophytes, which were giant salvinia, Salvinia molesta, and hygrophila, Hygrophila polysperma. Prymnesium parvum blooms have become more frequent in the south-central United States, leading to significant ecological and economic impacts. Allelopathic effects from cyanobacteria were suggested as a mechanism that might limit the development of P. parvum blooms. This research focused on the effects of cultured cyanobacteria, Anabaena sp., on P. parvum. Over a 6-d period, daily additions of filtrate from the senescent Anabaena culture were made to P. parvum cultures growing in log phase. All treatments, including several types of controls, showed reductions in P. parvum biomass over the course of the experiment, but the treatments receiving Anabaena filtrate were reduced to a lesser degree, suggesting that filtrate from the senescent cyanobacteria culture was beneficial to P. parvum in some way. Aquatic vegetation is an important component of most freshwater systems and provides numerous valuable ecosystem services, providing food, habitat and refuge for a variety of organisms. A significant threat to beneficial aquatic vegetation abundant in many United States waterways is the introduction and spread of invasive macrophytes. Two of the newest invasive species, giant salvinia (Salvinia molesta) and hygrophila (Hygrophila polysperma), have quickly established in Texas waters. This research evaluated the potential use of triploid grass carp (Ctenopharyngodon idella) as a biological control agent for these two novel invasive species. Using a controlled mesocosm experiment, consumption rates and feeding preferences were measured. Giant salvinia and hygrophila were compared to six native and introduced species common in Texas and the Southern US. Grass carp were found to be potentially useful in controlling giant salvinia in the preliminary stages of an infestation but an overall poor control option for hygrophila.Item Dynamics of woody plant encroachment in Texas savannas : density dependence, environmental heterogeneity, and spatial patterns(2010-08) González, Ana Verónica; Fowler, Norma L.; Schwinning, Susan; Linder, Craig R.; Leibold, Mathew A.; Meyers, Lauren A.Woody plant encroachment, that is, a substantial increase in the abundance of woody plants in a grassland or savanna, occurs in many parts of the world. It often has large effects on plant and animal populations and communities and on ecosystem properties and processes. However, little is known about the dynamics of woody plant encroachment and how these are affected by soils, by topography, and by the spatial pattern of the vegetation. Encroachment in turn can affect the spatial pattern of the vegetation. Using data from historical aerial photographs, I measured changes in woody plant cover and constructed, parameterized and compared a set of dynamic models of woody plant encroachment in central Texas savannas. These models predicted final woody cover from initial woody cover and the initial spatial configuration of woody plants. Then I incorporated soil and topography into these models to determine their effects. Finally, I examined the effects of encroachment on the spatial pattern of the vegetation. Incorporating negative density dependence in our models improved their fit, demonstrating that encroachment is density-dependent. A function that predicted the formation of new woody patches from a density-independent seed supply also improved the models' performance. The improvement in the models that resulted from incorporating the total length of woody-herbaceous edges confirmed that encroachment in this system occurs in part by the outward expansion of woody patches. The spatial pattern of the vegetation changed during woody plant encroachment. Spatial pattern (measured as degree of fragmentation) often had a non-linear relationship with cover. Furthermore, the spatial heterogeneity in fragmentation, that is, plot-to-plot variation in the degree of fragmentation, also changed during encroachment. Topography and soil type had, in general, little effect the dynamics of woody plant encroachment. Therefore, a relatively simple model of woody plant encroachment provided good predictions of woody cover at the end of the time periods. Other systems experiencing woody plant encroachment, forest succession, or invasion by non-native plants could be modeled using the same approach.Item Ecophysiology and ecosystem-level impacts of an invasive C4 perennial grass, Bothriochloa ischaemum(2013-12) Basham, Tamara Sue; Fowler, Norma L.; Litvak, Marcy E.The anthropogenic introduction of species into new ecosystems is a global phenomenon, and identifying the mechanisms by which some introduced species become dominant in their introduced ranges (i.e., invasive) is crucial to predicting, preventing, and mitigating the impacts of biological invasions. Introduced perennial C₄ grasses are invading semi-arid grassland and savanna ecosystems throughout the south-central U.S. We hypothesized that in these semi-arid ecosystems, where variable precipitation patterns strongly influence vegetation dynamics, the success of an invasive plant species may be due in part to ecophysiological traits that enable high performance in response to unpredictable water availability. We also hypothesized that increased primary productivity and decreased plant input quality associated with these grass invasions have the potential to alter ecosystem carbon and nitrogen cycling and storage by altering the ratio of inputs (productivity) to outputs (decomposition/respiration). We tested the first hypothesis by quantifying ecophysiological performance differences between an invasive C₄ grass, Bothriochloa ischaemum, and co-occurring C₃ and C₄ native grasses under wet and dry conditions in the field and under two levels of simulated precipitation frequencies in a greenhouse experiment. We tested the second hypothesis by examining whether increased primary productivity and decreased C₃:C₄ grass ratios in savanna grass-matrices associated with B. ischaemum invasion altered (1) plant input quality and thus nutrient cycling and/or (2) net ecosystem carbon uptake in invaded areas. B. ischaemum's success as an invader was not directly related to its ability to cope with precipitation variability and availability, but its ability to rapidly produce large amounts of biomass may allow it to directly out-compete native species. B. ischaemum invasion decreased plant input quality and soil nitrogen availability. B. ischaemum invasion shifted ecosystem C-uptake from being nearly year-round to occurring predominantly in the summer. Greater C-uptake during the summer and under drier conditions compensated for a shorter growing seasons in B. ischaemum-invaded areas and cumulative annual NEE was similar between invaded and native-dominated areas. We conclude that B. ischaemum's impacts on soil nitrogen availability and plant-canopy microhabitat may allow it to exclude native species from invaded areas, but that its impacts on ecosystem C sequestration may be small.Item Ecosystem under Pressure: Examining the Phytoplankton Community in the High Ballast Water Discharge Environment of Galveston Bay, Texas (USA)(2013-01-15) Steichen, Jamie LWith steady growth in global commerce and intensified ship traffic worldwide, comes the increased risk of invasion by non-indigenous organisms. Annually, >7000 vessels traveled across Galveston Bay, Texas from 2005-2010. These vessels discharged ~106 million metric tons of ballast water, equivalent to ~3.4% of the total volume of the Bay. A majority of these discharging vessels originated from around the Gulf of Mexico and the Caribbean Sea. By evaluating the source and frequency of inoculations from various locations, we are striving to assess the invasibility risk to Galveston Bay by way of ballast water. We identified organisms from Galveston Bay, ballast water samples and growout experiments using molecular methods. To our knowledge, this is the first utilization of molecular methods to identify the phytoplankton community within Galveston Bay. Within Galveston Bay, we identified 15 genera of dinoflagellates, 2 of which have previously gone undetected including Takayama and Woloszynskia. Thirteen ballast water samples yielded twenty genera of Protists, Fungi or Animalia from at least ten different phyla. With more than seven genera identified, dinoflagellates were the most diverse group: including the known toxin producer Pfiesteria and Scrippsiella which has not previously been detected in Galveston Bay. The most common diatoms in the ballast water samples were Actinocyclus, Ditylum, Nitzschia, Stephanopyxis and Thalassiosirales. At the termination of the growout experiments eight genera of phytoplankton were identified including: Dinophysis, Gymnodinium, Gyrodinium, Heterocapsa, Peridinium, Scrippsiella, Chaetoceros and Nitzschia. With these findings, Galveston Bay has the potential to be both a recipient and donor region of dinoflagellates. Dinoflagellates, capable of forming harmful algal blooms leading to fish and shellfish kills, are being transported to Galveston Bay via ballast water. Our results suggest that Galveston Bay is at risk for invasive species introductions via ballast water and support the idea that a monitoring system within the ports as well as the bay should be put in place. The actions would help to maintain the current health of this ecosystem and aide in preventing a negative impact in the event of successful establishment of a non-indigenous species of phytoplankton transported to Galveston Bay via ballast water.Item Effects of the Arundo donax L. on Hydrological Regime of the Rio Grande Basin(2012-07-16) Li, FanThis study investigated the role of an invasive tall cane, Arundo donax L. (Arundo), in the riparian water cycle. Four 100 meter transects were arrayed perpendicular to the lower Rio Grande in southwest Texas. The first objective was to determine the primary water source for Arundo by using naturally occurring stable isotopes. Surface soil, river water, groundwater, precipitation and rhizome samples were collected every month during 2010 and 2011 growing seasons, which coincided with a major flood that saturated soils in the first year followed by extreme drought in the second year. The second objective was to characterize how Arundo water use varied with water availability gradients in the riparian zone. Leaf gas exchange and leaf delta13C were measured along potential moisture gradients. The third objective was to understand the interaction between groundwater and surface water, and whether Arundo water use affected daily groundwater fluctuations. The isotope ratio of rhizome water was consistent with shallow soil moisture uptake and with previous observations of a relatively shallow, fibrous root system. Floodwater from July 2010 persisted in the soil for at least a year despite a severe drought, and became the dominant water source for Arundo during much of the study period. Although the alluvial water table in this floodplain was shallow (< 6 m) and subject to changes in river level, groundwater seemed not to be an important source for Arundo, so long as the soil moisture was sufficient. In this study, Arundo was not found to experience soil moisture limitation, and the spatial variability of Arundo transpiration was not associated with any soil moisture availability gradients. Arundo was found to close its stomata in response to increasing vapor pressure deficit (VPD), causing declining transpiration rate and increasing leaf delta13C composition. Significant exchange between the river and the alluvial groundwater was reflected in the similarity of isotopic compositions and the high correlation between river and groundwater elevations. Cross correlation analysis showed that over 50% of the diurnal groundwater fluctuations were caused by river stage changes. Consistent with the above ecophysiological and stable isotope results, Arundo water use was not found to influence daily groundwater fluctuations.Item Evaluation of Ships' Ballast Water as a Vector for Transfer of Pathogenic Bacteria to Marine Protected Areas in the Gulf of Mexico(2013-05-10) Morris, Theresa LAn average of three to five billion tons of ballast water (BW) is transported globally per year; 79 million tons of which is released into U. S. waters. Ballast water is necessary for large ships to maintain balance and stability while loading and unloading cargo as well as during transit. As a ship unloads it?s cargo at a port, it takes on ballast water and then when it loads cargo at the next port, it discharges the ballast water, thus transferring water from port to port. Aquatic organisms are transported around the globe via ballast water. These organisms can potentially cause serious environmental and human health impacts. Historically, transfer of macro-organisms such as fish, snails, and vascular plants via ballast water have been the focus of ballast water research. More recently, microorganisms such as toxin producing dinoflagellates and diatoms i.e. ?harmful algal blooms? and pathogenic bacteria (e.g. Vibrio cholerae), have been found to survive in ballast tanks for several weeks. These organisms have moved to the forefront of ballast water management (BWM) trepidations because they compose serious threats to human health as well as Marine Protected Area (MPA) ecosystems such as coral reefs. Ballasting activities of ships calling at the Port of Houston were used as a model for other major ports in U.S. Gulf States. Ballast water management reports, submitted to the U.S. Coast Guard by all overseas vessels calling at the Port of Houston in 2010 were examined for the ballast management strategies utilized prior to docking. Currently, all ?coastwise? ships are not required to conduct ballast water exchanges (BWE) if they do not transit beyond the 200nm EEZ. Close inspection of BW management report forms for ?overseas? ships determined that the degree of completeness was variable. By comparing the frequency of vessels entering the Port of Houston, ballast water capacities, the management types utilized, and the locations of ballast water exchanges and discharges, it can be concluded that larger vessels present the highest risk of bacterial transfer to coral reefs. Five coral diseases were discovered to be prevalent throughout the ballast management areas their presence has significantly increased in these areas over the past thirty years. The combination of this disease growth along with an increase in shipping and ballast exchanges suggests that the vector at which pathogens are being displaced must lie within the shipping lanes.Item Global change : projecting expansion of invasive species and climate change impacts at the tree-tundra ecotone in the Himalaya(2014-08) Mainali, Kumar Prasad; Parmesan, Camille, 1961-; Singer, Micheal; White, Joseph; Young, Kenneth; Simpson, BerylModeling the distribution of species, especially of invasive species in non-native ranges, has multiple challenges. We develop some novel approaches to species distribution modeling aimed at reducing the influences of these challenges and improve realism of projections. We estimated species-environment relationship with four modeling methods, viz., random forest (RF), boosted regression trees (BRT), generalized linear models (GLM), and generalized additive models (GAM), running each of them with multiple scenarios of (1) sources of occurrences and geographically isolated background ranges, (2) approaches of drawing background points, (3) alternate sets of predictor variables. When a species' distribution is in a non-equilibrium state, as is the case for most invasive species, model projections are very sensitive to the choice of training dataset. Contrary to previous studies, we found that model accuracy is much improved by using a global dataset for model training (both presences and background points from the world), rather than restricting data input to the species' native range. Projections outside the training region, especially in invaded regions, can be very different depending on the modeling method used. Globally projecting, we show that vast stretches of currently uninvaded geographic spaces in multiple continents harbor highly suitable habitats for Parthenium. Projections away from the sampled space (i.e. into areas of potential future invasion), can be very different with different modeling methods, raising questions about the reliability of ensemble projection. Data-driven models that efficiently fit the dominant pattern but exclude highly local features in dataset and model interactions as they appear in data (e.g., boosted regression trees) improve generalization of the species distribution modeling. Alpine treelines are responding to current climate change worldwide. To understand tree line dynamics and its potential drivers, we studied the primary two dominant tree species, Abies spectabilis (AS) and Rhododendron campanulatum (RC), on the north facing slope of two mountains in central Nepal. We determined spatial pattern of regeneration potential, mortality and abundance for various size/age classes, and we identified the most important drivers of such patterns. We also conducted a reciprocal transplant experiment on saplings of RC, moving them between species limit and treeline that were spaced apart by 150m. Young plants (<2m tall) of RC have higher density above treeline than below treeline. Mature plants (>2m tall) of RC, on the contrary, show insignificant trend towards higher density below treeline than above. Mortality of RC was always lower above treeline than below, independent of size class. AS saplings have extremely lower density above treeline than below, with mature plants being virtually absent above treeline. Elevation was identified as the only significant predictor of the decrease in density of both species above treeline. The saplings are progressively younger and shorter with distance above treeline. Both species are regenerating faster above treeline than below. These results are consistent with upward shift of the tree line of RC as a result of recent amelioration of temperature. Climatic extremes during spring affect mortality and leaf size whereas growth is affected by summer climate. Individuals from the species limit, if they survive, perform better when moved downhill than they do at home, and also out-perform the locals. Although the upper elevational boundary of RC is shifting upward, these results indicate that strong differences still exist between individuals across a short elevational gradient, with individuals at the extreme limit of the species range being more tolerant to extreme climate conditions but less tolerant of competition compared to individuals only 150m lower in elevation.Item Invasion risk and impacts of a popular aquarium trade fish and the implications for policy and conservation management(2014-05) Dugan, Laura Elizabeth; Hendrickson, Dean; Parmesan, Camille, 1961-Invasive species, a top threat affecting global biodiversity, become invasive through a process including four stages: transport, establishment, spread, impact and integration. Species currently in this process provide opportunities to empirically derive the mechanisms driving each of these stages, make predictions based on these mechanisms and then to test these predictions. This research examines the current invaded distribution, potential invasion and community-level impacts of a popular aquarium trade fish (Hemichromis guttatus Günther, 1862) in an endemic hotspot, Cuatro Ciénegas, in Coahuila, México and discusses the policy and conservation management implications of these findings. In Chapter 1, the problem of invasive species, the study site and the focal species of this work are introduced. In Chapter 2, the critical thermal minimum and maximum temperature limits and temperature preference of H. guttatus are identified because temperature is hypothesized to be an important factor controlling this fish’s distribution. The results indicate that H. guttatus has a wide temperature tolerance range (a characteristic of a ‘good’ invader), that preference is a more informative metric for predicting invasion than absolute tolerances, and that resource-poor environments may promote searching behaviors that cause an invasive fish to increase its range. In Chapter 3, the results of a field survey are analyzed and temperature, pH, depth and the presence of vegetation are all found to be related to H. guttatus presence. Invasion risk of several as-of-yet uninvaded sites in Cuatro Ciénegas is assessed. In Chapter 4, competitive and predatory interactions of H. guttatus on an endemic, threatened cichlid (Herichthys minckleyi) and a macroinvertebrate community respectively are investigated. The results suggest that while H. guttatus does not directly impact H. minckleyi through competition in these conditions, it may inhibit reproduction and alter H. minckleyi’s behavior through aggressive interactions. In Chapter 5, all results are synthesized and a determination of the invasive status of H. guttatus in Cuatro Ciénegas is made. The results presented here will be useful in identifying areas with a high risk of invasion by this popular ornamental fish, thus allowing the implementation of policy and management actions to prevent or at least ameliorate the impacts of an invasion and will add to the growing knowledge of how invasive species affect native systems.Item Investigation of an Invasive Ant Species: Nylanderia fulva Colony Extraction, Management, Diet Preference, Fecundity, and Mechanical Vector Potential(2012-11-15) McDonald, Danny 1983-Invasive species often threaten biodiversity and environmental processes in their introduced range by extirpating native species due to competition for resources. Nylanderia fulva (formerly N. (=Paratrechina) sp. nr. pubens) is an ecologically dominant and economically important invasive species in the United States. This dissertation addresses aspects of the biology, behavior, management, and collection techniques for N. fulva. Specifically, topics investigated include a modified drip technique for extracting ants from their substrate, the effectiveness of a broadcast ant bait as a stand-alone treatment, the foraging preference and peak activity of workers, the reproductive potential of queens, and the ability of this species to translocate pathogenic microorganisms. The primary goal of these works was to better understand the biological idiosyncrasies of this species that may ultimately lead to the mitigation N. fulva populations. A modified drip technique was developed to quickly and efficiently extract N. fulva from their nesting substrates. Ants and their associated substrates were collected in 18.9 L buckets lined with talcum powder and transported to the laboratory. Substrates were weighted down and a cardboard tower was provided for the immigration of ants as they were forced out of substrates with a slow influx of water. Three applications of Advance Carpenter Ant Bait (ACAB) were applied to a N. fulva population in East Columbia, TX. A series of GIS interpolated maps depict achieved management and subsequent rebound of N. fulva populations. As great as 77% population reduction was achieved by 1 week post treatment, but N. fulva populations rebounded within 3-4 weeks. As a stand-alone treatment, this bait did not provide adequate ant management in treatment plots. Diet preference experiments were performed using artificial diets and food lures. These results of these trials indicated that N. fulva preferred the most carbohydrate rich diet offered through all seasons and that mint apple jelly or hot dog slices were the favored food lures. Diel foraging behavior was observed when temperatures were between 9.95 and 37.26 degrees C. Peak foraging activity occurred at 28.24 +/- 3.12 degrees C. A laboratory investigation of N. fulva suggested that as the number of queens increased, individual queen fecundity increased. This phenomenon is a novel observation among ants and suggests an alternative mechanism for intracolony dominance. Hexagyne colony fecundity of 0.25 +/- 0.12 eggs/queen/hr was the maximum fecundity observed. Results of laboratory experiments showed that N. fulva were capable of transferring E. coli up to 4.5 m in 6 hrs after acquisition from a contaminated source. Pyrosequencing of ectomicrobial assemblages revealed a suite of 518 bacteria and 135 fungi species associated with N. fulva, many of which are known pathogens of plants and animals, including humans. These results suggested that N. fulva should be regarded as both a medically and agriculturally important species.Item Modeling the Hydrologic Impact of Arundo Donax on the Headwaters of the Nueces River Using the Swat Model(2014-08-06) Jain, ShaileeThe invasive species Arundo donax (hereafter Arundo), has invaded the riparian zones of the Rio Grande River and the rivers of the Texas Hill Country over the last two decades. Arundo, also known as the giant cane, is a robust herbaceous plant that can grow in many different climatic conditions. Arundo was first observed along the Nueces River in 1994 by the Nueces River Authority (NRA). It then spread rapidly downstream due to its high growth rate and/or stream flow and completely displaced the native vegetation, primarily P. virgatum (hereafter switchgrass), in the riparian zone wherever it got established. An eradication program was started in 2010 by the NRA to remove Arundo from the Nueces River. The objective of this research project was to (1) develop an algorithm to simulate the propagation of Arundo, (2) study changes in streamflow patterns during pre- and post- Arundo invasion periods, (3) calibrate and validate the Soil Water Assessment Tool (SWAT) for the Nueces River Headwater (HUC 12110101) watershed in central Texas, and (4) assess the effects of the invasion of Arundo on the watershed hydrology by comparing it to the native grass species switchgrass (Panicum virgatum) that used to be the dominant species in the watershed. Arundo parameters appropriate for the Nueces River were added to create a new crop category in the SWAT database. Calibration and validation of SWAT were based on measured streamflow data available at the USGS gage (USGS 08910000) on the Nueces River for the period 1960 to 1994. Switchgrass, the native vegetation, was chosen as the plant to compare Arundo with so that the difference in hydrology could be understood. The results revealed that accumulated evapotranspiration was not statistically different between Arundo and switchgrass for the period of 16 years (1995-2010). There was also no difference in the water yields of Arundo and switchgrass. In conclusion it appears that Arundo in the Nueces River has not caused any changes in water uptake compared to the native grass, switchgrass, that previously dominated the headwaters.Item Parasitism and Fatty Liver Disease in the Invasive Red Lionfish, Pterois Volitans (Linnaeus), Along the Gulf of Mexico(2017-11-14) Fails, Danielle M.; Cook, Tamara; Smith-Herron, AutumnInvasive species are detrimental to both the economy as well as to environmental stability. One of the most successful to date is the red lionfish, Pterois volitans, which first invaded the western hemisphere around 30 years ago. Lionfish have decimated native fish populations at roughly 7,500 lbs. per acre per year, have no natural predators, and seem fairly resistant to parasitism. Few species (<50) of parasites have been found in lionfish. Not only is parasitic prevalence low in lionfish, but they also seem to exhibit resistance to the effects of fatty liver disease. This research provides an updated parasite survey and reports six species of parasites, three of which are parasite species reported for the first time in lionfish; (1) one Cymothoid isopod: Olencira praegustator, (2) one Corallanidae isopod: Excorallana truncata, and (3) an acanthocephalan: Serrasentis sagittifer. Overall parasite prevalence and intensity was low for all hosts, and were significantly higher in males. A baseline study of fatty liver analysis in lionfish revealed that >85% of examined fish displayed evidence of fatty liver disease, and most exhibited moderate degrees of disease. Sex, location, and standard length of lionfish did not play a significant role in degree of disease, though slight disease differences were observed among locations. Outward condition (i.e. skin/scale integrity, coloration, observed mass) of specimens observed in relation to fatty liver disease and parasitism seemed relatively unaffected.Item A review of the impacts of invasive grasses on herpetofauna(2015-08) Wright, Ian Michael; Gilbert, Lawrence E.; Leibold, Mathew ASpecies invasions pose one of the greatest threats to the maintenance and stability of biodiversity in ecosystems across the globe (Vitousek 1990). Plant species in particular are uniquely predisposed to successfully invade and establish themselves in novel habitats. In the United States alone invasive plants are responsible for nearly 35 billion dollars in economic and environmental damage. Grasslands are among the most productive ecosystems in the US and their biodiversity is threatened by continual introduction of alien grass species. These invasive grasses have a variety of direct and indirect effects on native grassland communities and have the ability to alter fire regimes, displace native species, and simplify grassland food webs. Little is known about the impacts invasive grasses have to amphibians and reptiles but there is evidence to suggest that these and other small organisms suffer direct mortality, impoverished prey sources, and reduced reproductive opportunities as a consequence of grass invasions. Here I summarize the current literature surrounding invasive grass impacts on herpetofauna and suggest topics of further research.Item Root Water Uptake and Soil Water Dynamics in a Karst Savanna on the Edwards Plateau, TX(2013-05-09) Tokumoto, IeyasuWoody plants are encroaching into a karst savanna on the Edwards Plateau in central Texas, but their impact on hydrology is unclear because of high variability in soil depth and uncertainties about shallow and deep root contributions to water uptake, and water dynamics in rocky soil. The overall objectives of this study are to quantify contributions of shallow and deep roots to water uptake, and to quantify the impact of rock on soil hydraulic properties and water storage. A study was conducted in a karst savanna with ~50% woody cover to monitor spatial and temporal variations in soil moisture and root water uptake with neutron probe and time-domain reflectometry measurements. Bulk density was measured using gamma densitometry. Measurements were made to a depth of 1.6 m in a 25 m ? 25 m grid (5 m node spacing). The results showed that rock created high spatial variability in water storage. Water storage capacity in the measurement grid ranged from 185 to 401 mm, and coupled with heterogeneous distribution of trees led to high spatial variability in root water uptake. Most of the water uptake came from the upper 1 m of the soil profile, but 10% came from below 1.6 m. This indicated that roots had access to water stored within the bedrock, possibly in soil pockets. Statistical analysis showed that spatial distribution of ? was significantly correlated with rock distribution in the profile. Laboratory evaporation measurements showed that Small volume fractions of rock can increase evaporation from soils by slowing upward movement of water, thereby maintaining capillary connectivity to the surface for a longer period of time. Two simulation models, van Genuchten (VG) and Durner, were compared with the data from evaporation experiments. Results showed that the Durner model was more appropriate than the VG model for describing water retention and hydraulic conductivity of rocky soils.Item The Cuban tree frog (Osteopilus septentrionalis): distribution, diet, and reproduction of an invasive species in the British Virgin Islands(Texas Tech University, 2005-08) Owen, Jennifer L.; Perry, Gad; Densmore, Llewellyn D.; Thorvilson, Harlan G.; LeVering, KateInvasive species have the ability to inflict monetary and ecological damage on the systems they invade. Because of this, invasives and the characteristics that facilitate their invasion have received much attention including the compilation of set of key characteristics that make a species a successful colonizer. The Cuban tree frog (CTF) (Osteopilus septentrionalis) is an invasive species that has spread through Florida and the Caribbean. Because of its success as an invader, the CTF has been utilized as a model for examining successful invaders and invasions. To gain further insight into the CTF as a successful colonizing species, three of the putative characteristics of successful colonizing ability are investigated here through research on the invasive Cuban tree frog populations in the British Virgin Islands (BVI). The CTF is native to Cuba, the Bahamas, and the Cayman Islands. As a successful invasive species, the Cuban tree frog has increased its distribution and is now recorded as an invasive in Florida, Hawaii, Puerto Rico, Anguilla, Bonaire, the U.S. Virgin Islands, and most recently the British Virgin islands (BVI). In Chapter II, I examine one proposed characteristic of a successful colonizing species, the vagility of the CTF. This is accomplished by first establishing that CTFs are indeed populating the BVI, and then, tracking their spread throughout the islands. Since 1990, the CTF has been collected on five islands within the BVI, several of which I document for the first time. Four of the islands currently sustain breeding populations which were the basis for the studies that follow. I conducted an examination of the methodology of studying dietary composition. It is common in studies of the diet of reptiles and amphibians to solely rely on items found in the stomach. Chapter III addresses the potential biases entailed in this approach. Prey items found in the stomach and intestine were compared and found to be significantly different. I recommend the use of both methods to gain a complete view of a population’s diet and to gain a more complete view of what effect it may have on its prey. Chapter IV addresses another putative characteristic of successful colonizers, a generalist or broad diet. When the invasive CTF population in Florida was examined by Walter Meshaka, their diet was found to be quite broad, consisting of many orders of invertebrates as well as vertebrates. I assessed dietary breadth of the CTF in the BVI by analyzing stomach and intestinal contents of 428 frogs. Additionally, I examined the dietary plasticity of the CTF by comparing the diet of the CTF between islands within the BVI and between the BVI and Florida. Both traits, generalist diet and plasticity of diet, are demonstrated by the CTF. Chapter V focuses on another proposed characteristic of successful colonizers, high fecundity. I monitored reproductive ability and potential output in the BVI compared then to data collected by Meshaka in Florida. Both year-round reproductive ability and potential high reproductive output are present in the CTF population of the BVI, which also showed an increased body size, and increased clutch production compared to the Florida CTF population. On the whole, data collected on the CTF in the BVI support the validity of the proposed characteristics of successful colonizing species. This may help the ongoing increase in the CTFs range throughout the BVI, the Caribbean, and other novel habitats. Future research should be turned towards management and control methods for this pest species.Item The impacts of nitrogen utilization and allocation strategies on photosynthesis for an invasive grass, Phalaris arundinacea, in comparison to the native sedge, Carex stricta.(2012-08) Guvvala, Hasitha; Holaday, A. Scott; Schwilk, Dylan W.; Zak, JohnPhalaris arundinacea (reed canary grass) is an invasive C3 perennial grass of temperate/boreal wetland communities. It is more abundant in areas with high nitrogen (N) inputs. Our hypothesis is P. arundinacea gains a competitive advantage over Carex stricta, the native sedge it often displaces, with increased N, because it allocates more N to features that enhance net carbon gain than C. stricta does. To test this hypothesis, we are comparing the responses of photosynthetic parameters and leaf morphology to various N levels (0.15 to 45 mM N) for P. arundinacea and C. stricta. We grow the plants in a course medium whose N content is controlled by varying the nitrate and ammonium in standard Hoagland’s solution. With an increase in the N concentration provided, we observed an increase in net CO2 assimilation on an area basis (A), leaf N content, leaf area, and specific leaf area (SLA) for P. arundinacea, but the effect on chlorophyll content was not clear. At low concentrations of N supplied C. stricta, had the higher A, leaf N content and leaf area compared to P. arundinacea. It appears that N level affects total carbon gain for P. arundinacea by affecting A, leaf area, and SLA, allowing it to rapidly attain its full height and shade C. stricta. These advantages of high nitrogen had made the P. arundinacea become more aggressive and invade the wetlands displacing the C. stricta.