Announcement
The global distribution of the Reddish Egret is characterized by disjunct colonies ranging from the Pacific side of Northern Mexico to the Caribbean. We examined distantly isolated breeding colonies of Reddish Egrets to determine the genetic structure of the global population. We used nine polymorphic microsatellites to accomplish seven goals: 1) to assess range wide population differentiation among Reddish Egret (Egretta rufescens) populations, 2) identify extent of gene flow, 3) determine any historical occurrence of bottlenecks, 4) assess genetic differentiation between color morphs, 5) clarify subspecies status of E. r. dickeyi, a completely dark morph population located in and around Baja, Mexico, 6) assess paternity of clutches and, 7) determine offspring sex ratio. We collected blood samples of 223 nestlings, each from a separate nest, from colonies in Texas, Baja California, Bahamas, and Florida. In nests where all offspring were sampled, multiple paternity was identified 15.4% of the time. Offspring sex ratio did not deviate significantly from expected. Differentiation occurred between 3 distinct regions but not between colonies/islands within regions. Genetic diversity is lower in Baja, Mexico and Great Inagua populations than the Texas/Florida population due to minimal immigration between regions and historical population reductions. Dark and white color morphs when present within the same region showed little to no differentiation. Patterns of recent population bottlenecks are not evident in each of the 3 regional populations. With evidence of limited gene flow in addition to low genetic diversity and prospects of habitat loss, we recommend that Reddish Egrets be managed as 3 distinct or evolutionary significant units (Baja, Texas/Mexico, and Inagua). Furthermore, our results do not refute the current subspecies status of E. r. dickeyi.
The invasion of Bothriochloa ischaemum (common name: King Ranch (KR) bluestem) into North American grasslands has caused a marked reduction in the biodiversity of native flora and fauna. Prescribed burns during the winter have had little success in controlling KR bluestem, but there is new evidence that summer burns may be more effective. Using this observation as a starting point, I examined in two experiments whether a) the phenological status of a perennial grass at the time of the burn affects meristem survivorship and b) whether fire conditions (e.g. temperature and duration) affect seed germinability. Both experiments were designed to investigate whether the circumstances of a prescribed burn can be honed to maximize damage to the invader, while moderating damage to its native competitors. Experiment 1 consisted of two factorial field experiments with burn time (September or October) x precipitation (ambient or less than ambient), using rain-out shelters to exclude rain for some time leading up to the burn. Results from this experiment suggest that phenological and physiological status at the time of burn can affect the ability of KR bluestem to re-grow in the following spring. Experiment 2 was a lab experiment, where I exposed the seeds of 6 species (KR bluestem and 5 natives) to heat of various temperatures and durations to simulate a range of fire conditions. Results from this experiment indicate that, in general, seeds of KR bluestem were less damaged by heat but moderate fire conditions were less damaging to native species. Both experiments suggest that it should be possible to develop a strategy for designing prescribed burns as a more selective tool for invasive species control.
The spread of urban and suburban habitats into what were once rural and undeveloped lands has left urban green spaces as refuges for wildlife populations in otherwise inhospitable environments. As human populations grow, so does the use of these green spaces for recreational activities. This study examined the effects of human recreational activities within green spaces on bird populations in Sunset Valley, Texas, an urban/suburban habitat southwest of Austin, Texas. Thirty fixed-radius point count stations were placed on walking trails throughout the city. Each point was visited five times during each of four seasons. I recorded birds seen or heard at each point count station, their distance from the center of the point, the number of recreationists passing through the point count site, and decibel levels at the point for a five minute duration. Vegetation information was taken at each point before and after leaf drop using a vegetation profile board and a densiometer. I use d a principal component analysis (PCA) to describe habitat characteristics at each site and a canonical correspondence analysis (CCA) to assess relationships between bird species, habitat, season, area of the study site, and recreational activities. I also conducted univariate tests to determine the relationship between urban bird guilds and different habitat and anthropogenic variables. The full model of the CCA explained 44.7% of the observed variation within bird abundances with the pure effects of habitat explaining 26.1 percent of the variation (P = 0.002) and season explaining 2.4 percent (P = 0.002) of the variation. Pure effects of area (0.9%; P = 0.18) and anthropogenic disturbances (4.9%; P = 0.11) were not significant. Univariate parameters significant in the stepwise procedure were mean canopy cover (17%; p = 0.002), mean vertical vegetation cover (6%; P = 0.002), area (5%; p = 0.002), high decibel level (5%; P = 0.002), and percent Ashe juniper cover (2%; P = 0. 05). My results indicate that vegetational characteristics are the main factor influencing bird populations in urban/suburban habitats, followed by the mean maximum decibel level at each point. My results also suggest that bird species that are already stressed under urban/suburban environments may be excluded from areas where decibel levels are too high.
The ocelot (Leopardus pardalis) was placed on the United States federal endangered species list in 1982. Historically these felids were hunted for their pelts, but other factors have contributed over the years to their placement on the list. Today, the major factor that causes ocelots to be endangered is loss of habitat. Previous research has demonstrated that ocelots prefer habitats of dense shrubs with greater than 95% canopy cover. However, little else is known about the total composition of vegetation in their habitat. The objectives of our study were to develop a geographic information system (GIS) containing vegetation, soil and satellite imagery for seven counties (Willacy, Cameron (Laguna Atascosa National Wildlife Refuge), Starr, Hidalgo, Jim Hogg, Kenedy, and Zapata) in South Texas to enhance prior research and define areas suitable to support ocelots. Ground-truthing on vegetation transects on public and private land across these counties was performed using a dens iometer, vegetation profile board (VPB), and Daubenmire frame techniques to determine key vegetative characteristics that comprise ocelot habitat. Through principal components analysis (PCA), we analyzed slope and intercept (VPB measures), percent canopy cover (overstory), percent grass, litter, bare ground, and forbs from Daubenmire frames, woody species richness, woody plant density, woody plant diversity, and average woody plant height per transect. We found the majority of ocelot habitat was characterized by greater plant diversity, greater vertical cover density at ground level, greater canopy cover, smaller shrubs, and more ground litter than habitat not occupied by ocelots. Along an east-west gradient in South Texas, eastern sites were more similar to ocelot habitat. Comprehensive vegetation information (i.e. plant density, percent grass, etc.) is lacking on satellite/ land-use images. Therefore, comparing habitat data through PCA analysis would be more effective in d elineating ocelot habitat.
Ecological surveys are a snapshot in time, providing biological inventories and important documentation about ecological communities. These data may be used to estimate population sizes and demographics as well as community parameters such as abundance, species richness and diversity. The results of such surveys assist land managers and agency personnel to formulate conservation protocols and serve as important tools in assessing impacts of conservation efforts and temporal changes in community parameters. Herpetofauna and rodents are particularly important because they are easily monitored, locally abundant, and have been used as indicator taxa of ecosystem diversity and health. From January 2008 to June 2009, amphibians, reptiles, and mammals of Palmetto State Park and the Ottine Wetlands were surveyed to produce a current mammalian and herpetofaunal inventory and produce estimates of relative abundance, evenness and diversity. I compared my data to the results of a sur vey performed in the late 1950s by Gerald Raun to determine if the composition of this community has changed through time or in relation to land use practices (agriculture vs. preserve/outdoor recreation). Standard survey methods were used equally among sites to sample amphibians, reptiles, and mammals. A total of 862 amphibians and reptiles representing 38 species (9 amphibians, 29 reptiles) were captured or observed. Time constrained counts (46.2%), nocturnal road surveys (30.9%), and drift fence arrays (10.1%) produced the highest amount of observations. Direct comparisons suggested noteworthy changes in the relative abundance within the snake assemblage between 1958 and 2008 despite little observed change in estimates of diversity and evenness. These data suggested that community composition of the herpetofauna has changed over the past 50 years resulting in a loss of amphibian richness (loss of five species) and changes to the composition and relative abundance of species within the reptile assemblage. Twenty-nine mammalian species were documented during the study. Differences in rodent evenness estimates approached significance with the private wetlands yielding higher values for species abundance and evenness. Furthermore, a greater richness and abundance of species within all groups were observed at the wetlands contained within boundaries of Palmetto State Park, compared to adjacent privately owned wetlands of Ottine. I propose that these changes resulted from changes in ground water availability through time (droughts and increased anthropomorphic use) and the geophysical attributes of the wetlands. Assemblage compositions between sites are consistent with differences in land use practice.
Central to evolutionary biology are questions concerning the origin and maintenance of biodiversity. As all species have arisen out of previously existing taxa, investigations often seek to explain prominent examples of morphological variation within species. Color polymorphism is a widely studied example. The mottled rock rattlesnake (Crotalus l. lepidus) exhibits striking levels of color polymorphism associated with two distinct substrate types. I hypothesize that selective predation on high contrast color and blotching patterns for the two respective regions maintains the differing phenotypes. I performed predation experiments with urethane foam snakes at 12 field sites in the west Texas portion of the species range. The field sites were split between the eastern region composed primarily of light colored limestone and the western region composed primarily of dark volcanic rocks. Two color treatments were used; one mimicking the light colored eastern race and one the dark colored western race. Additionally, these models varied in their blotching pattern. Half had no blotching to simulate the eastern race which has high proportions of anterior blotch fading. The other half of the models were painted with complete blotching to simulate the western race resulting in four total treatments. I found that high contrast color models were attacked significantly more often; however there was no difference in the frequency of attacks on the different blotching treatments. Additionally, there were no significant differences in non-predator disturbances between the different color or blotching patterns. Predation attempts occurred significantly closer to the anterior end of models than did non-predator disturbances. These results are consistent with the hypothesis that color pattern has been maintained by selective predation. Despite a lack of difference in attack frequencies on the different banding patterns, differing behaviors may be influencing selective predation; however additional work is required to determine if this is occurring.
Ecosystem engineers can affect resource levels, habitat availability, nutrient cycling, and trophic dynamics. Invasive armored catfish (Loricariidae: Hypostomus sp.) in the San Marcos River (Texas) are of concern due to their potential to reduce algal resources, alter benthic sediment transport, and affect nutrient cycling. In contrast, native big claw river shrimp (Macrobrachium carcinus) are large and omnivorous which may affect sediment transport and organic matter (OM) processing. I present a two-part study in which I examined the influence of these two consumers on ecosystem processes in the San Marcos River. The first part of my study is a replicated stream channel experiment which examined the individual and interactive effects of these two species on ecosystem function. The presence of catfish decreased periphyton biomass, altered nutrient ratios of periphyton, and increased sediment transport and OM decomposition. The presence of shrimp affected sediment transp ort, but had little overall effect. However, the presence of shrimp mediated the effects of catfish on periphyton biomass and nutrient ratios. The second part of my study examined the nutrient excretion rates and ratios of invasive catfish and thirteen other common fish species from the San Marcos River. Fishes exhibited large variation in body nutrient composition (N, P) and nutrient excretion rates and ratios. Fish body nutrient content and excretion differed among the fishes, with body size and taxonomy (at the species and family level) influencing body stoichiometry and nutrient recycling. Invasive Hypostomus sp. exhibited among the highest P content, lowest mass-specific P excretion rates, and the highest excreted N:P of fishes examined in my study. My results indicate that variation in nutrient recycling in fishes is a function of phylogenetic constraints on stoichiometry, suggesting that variation in river fish community composition can influence ecosystem nutri ent recycling.
Astrocytes play a major role in nerve regeneration of the central nervous system. In response to any central nervous system (CNS) trauma or pathology such as neurodegeneration or ischemia, astrocytes react by exhibiting hypertrophy of their cellular processes and hyperplasia (proliferation), a process referred to as reactive astrogliosis. Reactive astrogliosis can be modeled in vitro using mechanical (scratch wound) or chemical stimuli to activate F98 rat glioblastoma cells from a quiescent state to a reactive-like state. Studies have shown monoclonal antibody (mAB) J131 may recognize a phospho-epitope found on the nuclear intermediate filament, lamin, as well as the cytoplasmic intermediate filament characteristic to mammalian astrocytes, glial fibrillary acidic protein (GFAP), suggesting that mAB J131 is an appropriate marker for astrocytes entering the reactive state. Reactive astrogliosis, as detected by increased labeling of cytoplasmic and nuclear epitopes by mAB J313, can be modeled in vitro by treatment of F98 cells with forskolin, an activator of adenylyl cyclase. Here I tested the hypothesis that a cAMP-mediated intracellular pathway is involved in eliciting reactive astrogliosis, and I attempted to elucidate that pathway using inhibitors of known cAMP-dependent downstream signaling molecules and Ca+2 fluorescent indicators and characteristic nuclear labeling of F98 cells by mAB J131. Forskolin was found to significantly up-regulate mAB J131 antigen expression in as little as 10 minutes, reaching a maximum after 30 minutes. Pretreatment of F98 cells with the protein kinase A (PKA) inhibitor, H89, abolished the effect of forskolin, while inhibitors of protein synthesis and L-type calcium channels had no effect. Forskolin was found to induce transient cytoplasmic increases in Ca+2 levels (as measured by Oregon Green conjugated to BAPTA-dextran), and the relation of this to PKA is currently under further investigation. On the basis of these results, it appears that induction of cAMP production in F98 cells results in a PKA dependent increased phosphorylation of cytoplasmic and nuclear intermediate filaments, which may indicate the first stages of F98 cell transition from normal to a reactive state. On the basis of the rapidity of the response, it is unlikely that nuclear pathways are involved.
The emergence of bacterial resistance to bacteriophage is a major obstacle for the use of phage in the treatment of bacterial disease. Studies have focused on the effect of phage infection in single-species planktonic cultures. In chronic disease, bacteria are most often found in mixed species biofilms. This study investigates the effects of mixed culture growth on bacterial susceptibility to phage infection. Escherichia coli was challenged with phage W60 and Pseudomonas aeruginosa was challenged with phage PB-1. Phage W60 infection of the two-species cultures resulted in the extinction of E. coli in planktonic but not biofilm populations. In contrast, monoculture planktonic and biofilm populations of E. coli were stable in the presence of W60. P. aeruginosa maintained high cell densities in all culture conditions when infected with its phage, PB-1. The heightened susceptibility of E. coli to its phage may be due in part to competition with P. aeruginosa. This is the first re port on the effect of bacteriophage infection in a mixed species biofilm and demonstrates the advantage bacterial populations gain by forming biofilm communities.
Diurnal rhythms allow organisms to synchronize physiological functions, such as feeding habits, with environmental cues such as light and temperature. Much is known about the diurnal and/or circadian regulation of neurotransmitters that act on G-protein coupled receptors (GPCRs) but there is little to no knowledge of the diurnal or circadian regulation of the receptors. This study sought to determine whether there was a diurnal pattern of gene expression for muscarinic and dopaminergic GPCRs and the GPCR regulator, arrestin. Real time quantitative polymerase chain reaction employed on mRNA extracted from whole eye of zebrafish at four timepoints - dawn, midday, dusk, and midnight - indicated a diurnal pattern of gene expression for 6 genes out of 15 analyzed, arrestin, D2A, D4A, D4C, M2, and M5. Reverse transcriptase-PCR of mRNA extracted from different regions of the eye was used to localize expression of the statistically differentially regulated genes. Immunohistochemical analysis of the muscarinic M3 receptor and arrestin revealed the protein to be localized to different layers within the retina depending upon the time of day. Taken together, these results suggest that dopaminergic and muscarinic receptors, which have been implicated by others in the regulation of various circadian and diurnal processes in the eye, are themselves along with arrestin subject to diurnal regulation.
The persistence of vertebrate unisexual-bisexual mating systems is of interest for evolutionary biologists because theory predicts that the unisexual species in the complex should go extinct relatively quickly for several reasons: lack of genetic recombination and accumulation of deleterious mutations, competition with heterospecific females for access to males, a two-fold reproductive advantage over the sexually reproducing species which will lead to the extinction of both species, and selection on the males to discriminate against heterospecific females.
The world is experiencing an increase in emergent infections as a result of a world market, urbanization and intensified animal husbandry. It is not just humans affected, but also domestic and wild animals. Many diseases affecting humans are of animal origin and because of population increases and globalization of society we will continue to see increased interactions between humans, domestic animals, and wildlife. The wildlife component of this triad has received inadequate focus in the past to effectively protect not only human health, but biodiversity, agriculture and trade.
Actinorhizal plants are characterized by their ability to form root nodules in symbiosis with the nitrogen-fixing bacterium Frankia which enables them to grow on sites with restricted nitrogen availability. They are therefore uniquely successful pioneer plants, frequently establishing themselves after environmental disturbances, but have also potential for use in forestry, e.g., as nurse trees in mixed plantations with valuable tree species. The establishment and success of the symbiosis depends on environmental conditions, but is ultimately determined by the genotypes of both partners of this symbiosis. Since very little is known about Frankia in soil, the current study was focused on the fate of introduced Frankia strains in soil and potential effect of simple and complex carbon sources on its saprophytic growth. Furthermore, the potential limitations of the bioassay analysis which is most commonly used method to study Frankia in soil were also highlighted. A major outcome of this study was the determination of differences in C source utilization of different Frankia strains that have the potential to serve as inoculum. This information could possibly be used for the establishment of an effective symbiosis from the applied point of view. The study has also demonstrated the role of plants in the selection of frankiae from soil for root nodule formation and the inadequacy of bioassays for the analysis of frankiae in soil, and highlights the need for methods enabling the direct analyses of Frankia populations in terrestrial environments.
Actinorhizal plants are characterized by their ability to form root nodules in symbiosis with the nitrogen-fixing bacterium Frankia which enables them to grow on sites with restricted nitrogen availability. They are therefore uniquely successful pioneer plants, frequently establishing themselves after environmental disturbances, but have also potential for use in forestry, e.g., as nurse trees in mixed plantations with valuable tree species. The establishment and success of the symbiosis depends on environmental conditions, but is ultimately determined by the genotypes of both partners of this symbiosis. Since very little is known about Frankia in soil, the current study was focused on the fate of introduced Frankia strains in soil and potential effect of simple and complex carbon sources on its saprophytic growth. Furthermore, the potential limitations of the bioassay analysis which is most commonly used method to study Frankia in soil were also highlighted. A major outcome of this study was the determination of differences in C source utilization of different Frankia strains that have the potential to serve as inoculum. This information could possibly be used for the establishment of an effective symbiosis from the applied point of view. The study has also demonstrated the role of plants in the selection of frankiae from soil for root nodule formation and the inadequacy of bioassays for the analysis of frankiae in soil, and highlights the need for methods enabling the direct analyses of Frankia populations in terrestrial environments.
Landscape conversion to urban and agricultural use can alter adjacent ecosystem properties, including stream water chemistry. The purpose of my study was to evaluate landscape-water chemistry interactions in a subtropical karst system at multiple spatiotemporal scales. Landscape characteristics (natural and anthropogenic) were quantified at three spatial scales (sub-catchment, riparian, stream reach) and related to water chemistry measures collected over a 13-month sampling period. An additional dataset was incorporated into analysis to evaluate seasonal and long-term (1984-2008) temporal trends across contrasting stream flow conditions.
Ecosystem functions, such as primary production, decomposition and community respiration in aquatic systems, are linked to abiotic factors and the functional roles of taxa inhabiting the system. I performed two experimental case studies to examine stream ecosystem function influenced by different mechanisms. The first study investigated the individual and interactive effects of native and non-native species on ecosystem function. I performed a 2 × 2 factorial experiment using the large-bodied native big claw river shrimp (Macrobrachium carcinus, Decapoda: Palemoides) and the invasive armored catfish (Hypostomus sp., Loricariidae), as my model species. Armored catfish significantly influenced ecosystem function by decreasing periphyton abundance, facilitating leaf breakdown, increasing sediment transport and reducing invertebrate collector-gatherer abundance. Shrimp decreased periphyton biomass, and interfered with periphyton consumption by the invasive catfish. This study shows that invasive armored catfishes influenced biodiversity and affected ecosystem functioning. The second experimental study investigated the effects of an abiotic process, i.e., benthic sand-sediment movement, on leaf litter breakdown and invertebrate community colonization. Leaf detritus in streams is often a major source of carbon and energy for the system, as well as habitat for benthic invertebrates. Low gradient sandy bottomed streams retain leaf detritus via the periodic covering and uncovering of detritus with sand substrate. I tested the hypothesis that burial of leaf litter in sand would alter the invertebrate community composition on leaf packs, and slow detrital decomposition. The results of the natural stream experiment indicate that leaf burial status at sampling time was the key factor influencing invertebrate abundances on leaf litter. Burial of leaf litter did not influence detrital decomposition in the short term. This study supplies the ecological understanding of community-scale consequences of sediment movement in a sandy bottomed stream ecosystem.
I compared presence and/or absence of White-winged Doves (Zenaida asiatica) and Mourning Doves (Z. macroura) in south Texas to the 2001 National Land Classification Database (NLCD) categories. My objective was to determine which, if any, category (or categories) from the NLCD classification scheme could be used to predict species occurrence. My study was conducted between 15 May and 15 August 2007 and 2008. I used point transect methodology to conduct presence/absence surveys of White-winged and Mourning Doves at 236 points encompassing 744 observations. Land classification categories were quantified using geographic information systems (GIS). Each point and a 300-m buffer were projected on NLCD maps. I then used GIS to determine proportions of each land classification type within the buffer area. Randomization tests were used to compare proportions of land cover types present at points with and without doves. I then used Program DISTANCE to determine if land cover types found to be associated with dove presence had a higher estimated density than those with lack of dove presence. My results indicated that White-winged Dove occurrence in south Texas was positively influenced by land cover categorized as urban and cropland, while Mourning Doves showed a positive affiliation only to crop land cover types. In land cover types found to be associated with dove presence, estimated density increased based on percentage land cover.
Astrophytum asterias is federally listed endangered and in the United States is found only in Starr County, Texas. It has a priority ranking of 2 by the U. S. Fish & Wildlife Service which means it has high recovery potential. One means to achieve recovery is by reintroduction. This study characterized A. asterias habitat by conducting vegetation transects and collecting soil samples. A pilot reintroduction was also established. Of the 15 A. asterias subpopulations sampled 9 were classified as saline-sodic; 2 saline; 2 sodic; and 3 non-saline, non-sodic. The five plant species with greatest dominance included: Varilla texana, Prosopis glandulosa, Acacia rigidula, Opuntia leptocaulis, and Castela erecta subsp. texana. Seeds and seedlings were used as propagule material for the pilot reintroduction. A total of 240 of each were planted in two treatments, spring and fall. Less than 4% of the planted seeds germinated. Seedling survivorship of the spring and fall treatments was 55 and 72.5%, respectively. Mortality of the seedlings was due to desiccation, herbivory, infestation by weevils, and burying by Mexican ground squirrel. Twenty-eight candidate models were developed to assess the potential influence of season of planting; state of the seedlings; precipitation; ground temperature; seedling diameter at the time of planting; and percent bare ground of each subquadrat on percent survivorship of the reintroduced seedlings. A temporal model was also included which assessed passage of time as the only factor influencing survivorship. Of the model statements analyzed, the temporal model was the best model (AICc = 1129.3094, Akaike weight = 0.99999854). Based upon this research, a draft reintroduction plan for A. asterias was developed to guide future reintroductions.
I collected 147 common musk turtles from Spring Lake, San Marcos, Hays County, Texas between April 2008 and February 2009, to examine their dietary habits based on fecal analysis. I collected 70 female and 77 male turtles from lentic and lotic areas of the lake during spring, summer, fall and winter. After voiding their digestive tract contents all turtles were returned to the point of capture. Fecal matter was sorted into five component categories: gastropods, crayfish, insects, plant matter and other. Five items per category per sample were identified to the lowest possible taxonomic level, resulting in the identification of 5 types of gastropods, 1 bivalve, 1 crayfish, 13 insects, 12 plants and 4 additional taxa. After identification samples were dried and weighed. Gastropod material was the most abundant component of fecal material, followed by crayfish. I performed 3-way ANOVA tests of fecal component categories across three independent variables: habitat, gender and season. The percent weight of gastropods, crayfish and plants showed significant seasonal variation, while the percent weight of insects showed greater variation by habitat. The results of the qualitative identification of food items agrees with previous research.
Although the educational evaluation process is useful and valuable and is supported by the Higher Education Act, there remains a lack of a strong research base for program evaluation of college entry-level science courses. Studies in science disciplines such as, biology, chemistry, and physics have addressed various affective and demographic factors and their relationships to student achievement. However, no studies were found that specifically address student biology content knowledge skills (basics and higher order thinking skills) and identify factors that address students’ success in entry-level college science courses. These gate-keeping courses require detailed evaluation if an institution’s goal is to increase students’ performance and success in these courses, which is, in fact, a stepping stone for increasing the number of graduates in STEM majors. The present study measured students’ biology content knowledge and investigated students’ performance and success in college biology, chemistry, and physics entry-level courses. Six variables–gender, ethnicity, high school GPA, high school science, school financial aid support, and work hours were used as independent variables and course final performance as a dichotomous dependent variable. The sample comprised of voluntary student participants of entry-level science courses. The study attempted to explore eight research questions. Content knowledge assessments, demographic information analysis, multiple regression analysis, and binary logistic regression analysis were used to address research questions. The results suggested that high school GPA was a consistent good predictor of students’ performance and success in entry-level science courses. Additionally, high school chemistry was significant predictor variable for student success in entry-level biology and chemistry courses. Similarly, students’ performance and success in entry-level physics courses were influenced by high school GPA and high school physics course respectively. Finally, the study developed student success models with high school GAP, high school chemistry, and high school physics as good predictors of students’ success in entry-level biology, chemistry, and physics respectively.
Auxin is a pivotal plant hormone that plays a major role in plant growth and development. While Indole-3-acetic acid (IAA) is the major natural auxin found in plants, there are many synthetic chemicals with auxinic activity. 1-Naphthylacetic acid (1-NAA), 2, 4-dichlorophenoxyacetic acid (2, 4-D) and picloram are some examples of synthetic auxins. Of these, 2, 4-D and picloram are commonly used as herbicides in agriculture. While both natural and synthetic chemicals exhibit similar effects on plants, these chemicals are structurally different. Whether these structurally different chemicals function through similar molecular mechanisms is not known. Initial work in our laboratory indicates that picloram may function differently from other commonly known auxins. To identify genes that are associated with picloram response, we used a forward genetics approach to isolate Ethyl methanesulfonate (EMS) mutagenized Arabidopsis mutants that were resistant to picloram.
Molecular tools were developed to overcome some of the constraints to analyzing nitrogen-fixing bacteria in the environment. Two distinct plant-microbe systems were used to develop these tools, and to evaluate their utility and flexibility. The first system focused on nitrogen-fixing bacteria in the rhizosphere of salt-meadow grass (Spartina patens), a key plant species in high salt marshes. Members of the ε-subdivision of Proteobacteria were shown to be prominent nitrogen-fixers in this system, with specific populations changing seasonally and in response to the presence of arbuscular mycorrhizal fungi. The second system involved nitrogen-fixing bacteria of the genus Frankia that form root-nodules in symbiosis with certain woody plants. The diversity of nodule-forming frankiae was assessed in soils from 5 continents, and in natural populations in root nodules of alder trees growing on 3 different sky islands in southern Arizona. These studies provided significant databases for specific target sequences, i.e., the nifH gene, for both uncultured nitrogen-fixing members of the ε-subdivision of Proteobacteria and cultured and uncultured frankiae, and baseline data that demonstrated the usefulness of the molecular tools for studies on the ecology of both nitrogen-fixing members of the ε-subdivision of Proteobacteria and Frankia populations.
Microhabitats of small anurans are being encroached upon by land development in central Texas. Blanchard’s cricket frog (Acris crepitans blanchardi) is a small frog occupying small streams in these areas of disturbance. I investigated microhabitat affinity of Blanchard’s cricket frog to assess possible variability in microhabitat use due to disturbance in rural and urban areas of central Texas. Vegetative and substrate characteristics and moisture profiles of microhabitats were quantitatively assessed and categorized using line intercept and quadrat methods. Morphological data were analyzed by principal component analysis to depict associations of morphological characteristics to microhabitat association. I collected 424 Acris crepitans blanchardi from May to December 2008 in 12 rural and 12 urban habitats along Barton Creek and Onion Creek watersheds. Chi-square goodness of fit test indicated microhabitat affinity by cricket frogs was influenced by moisture level and substrate type. There was no difference in the distribution of cricket frogs between urban and rural environments. Analyses of morphological characteristics by PCA indicated larger cricket frogs associated with areas of dense vegetation in the more arid rural locations. I did not find that the current level of human-induced disturbance has affected microhabitat use by Blanchard’s cricket frogs; however, I would suggest a good management practice would be the establishment of a buffer zone in association with riparian habitats in central Texas.
North America holds the most diverse temperate freshwater fish assemblage in the world (S = 790). However, human actives such as dewatering and stream impoundment degrade stream-dwelling fish habitat and threaten biodiversity through extirpation and extinction. Purposes of my study were to address how riverscape fragmentation and altered flow regime have affected species abundances and fish assemblages in the Guadalupe and San Marcos rivers of Texas, and to develop habitat suitability criteria for conservation of the imperiled Texas state fish Guadalupe bass. Historical fish collections and stream flow data (1938-2006) were analyzed using Indicators of Hydrologic Alteration, linear and joinpoint regression, and multi-dimensional scaling to assess changes in fish composition and abundance related to instream and watershed stream flow alterations. Reductions in the number of small and large floods associated with impoundment was correlated with significant changes in species abundance (i.e., b1 ≠ 0, P < 0.05 for n = 47 taxa) and assemblage composition (i.e., ANOSIM global R = 0.409, P < 0.01 Guadalupe; R = 0.19, P < 0.01 San Marcos). Results from this study indicate instream and watershed stream flow alterations have impacts on stream fish communities, specifically causing increased abundance of cosmopolitan and lacustrine-adapted fishes and decreased abundance of obligate riverine fishes.
Numerous spring systems in the Edwards Plateau and Trans-Pecos regions of Texas support parapatric fish assemblages, spring-associated species and riverine species. Previous studies have identified constant water temperature as the segregating factor but have lacked the ability to effectively distinguish temperature from headwater influence. Multiple spring sources along a 64 km course of the Devils River, Texas allowed an opportunity to assess the influence of temperature and other variables (i.e., current velocity, depth, substrate) on spatial and temporal patterns in the fish assemblage. Physical parameters (10.6%), site (4.9%), and season (1.6%) explained 19.6% (CCA, P<0.01) of the Devils River fish assemblage. Current velocity, depth, and vegetation were among the strongest factors explaining fish segregation. Astyanax mexicanus and Cyprinella proserpina were generally found in riffle habitats, Etheostoma grahami, and Notropis amabilis were found in runs with moderate current velocities and depths, and Micropterus salmoides, Lepomis macrochirus, and Dionda diaboli were found in the deeper, vegetated pools. Water temperature influenced seasonal movement of spring associated species (i.e., A. mexicanus, N. amabilis, C. proserpina, Dionda argentosa, and E. grahami) into spring outflow habitats during summer and winter and resulted in a segregated assemblage. Surprisingly, the abundance and distribution of the federally threatened Dionda diaboli, a species listed as a spring-associate, did not correlate with spring outflows and was found diffuse throughout the Devils River. This study suggests spring flow (i.e., current velocity and depth) and constant water temperature are segregating factors and important for maintaining parapatric assemblages.
The potential role played by the host plant or the soil type in the selection of symbiotic, nitrogen-fixing Frankia strains from soil for root nodule formation was assessed by using molecular techniques. The diversity of Frankia populations in the root nodules of twelve Alnus species grown sympatrically was analyzed using rep-PCR (Repetitive Extragenomic Palindromic polymerase chain reaction). Analysis of 120 root nodules, i.e. 10 root nodules from each plant species revealed three rep-profiles which indicated the presence of only three Frankia strains in the root nodules. No variation was detected in Frankia populations among the root nodules of a single plant species, i.e., all nodules from one plant species had identical rep- profiles. Comparative sequence analyses of nifH gene fragments from three Frankia strains representing each rep-profile assigned these frankiae to different subgroups within the Alnus host infection group. None of these sequences, however, represented frankiae detectable in soil as analyzed by sequence analysis with 73 clones from a nifH gene clone library from frankiae in soil. Additional analyses of nodule populations from alders growing on different soils demonstrated the presence of different Frankia populations in nodules for each soil, with populations showing identical sequences in nodules from the same soil, but differences between plant species. These results suggest that soil environmental conditions and host plant species have a role in the selection of Frankia strains for root nodule formation and this selection is not a function of the abundance of a Frankia strain in soil.
In short lived phytophagous insects specialized to exploit specific plant tissues, phenological synchronization between plant and insect life cycle events is crucial and likely under selection. Here I report on past (1995¬–2001) and recent (2006–2007) patterns of emergence phenology and survivorship of the asexual generation of the host specific gall-former, Belonocnema treatae (Hymenoptera: Cynipidae) that develops within leaf galls on Quercus fusiformis, live oak. Comparisons of these patterns document an apparent shift in the timing of B. treatae emergence (Past: Oct.–Dec., Recent: Dec.–Mar.) and survivorship (Past: 0–50%, Recent: 0–13%) in the presence of natural enemies. These shifts in conjunction with past and recent defoliation of live oaks by oak leaf rollers (which alter the timing of tissue formation coinciding with B. treatae oviposition) motivated a manipulative experiment that tested the following hypotheses: variation in the timing of leaf formation, induced by defoliation, creates temporal variation in the timing of oviposition, affecting subsequent gall maturation schedules, and B. treatae emergence phenology and survivorship. On each of five trees, 48 screen enclosures were placed around branches and B. treatae were allowed to oviposit into (1) the initial spring leaf flush (n = 24 enclosures), and (2) a six–eight week delayed leaf flush (n = 24 enclosures) induced by stripping braches of leaves to mimic natural defoliation. After each oviposition event, 12 of the 24 enclosures/flush/tree were then opened to allow natural enemies to attack throughout development. Galls were monitored throughout development, harvested at maturity and placed in collection traps. B. treatae emergence phenology was monitored by weekly surveys and survivorship, in the presence and absence of natural enemies, was calculated by the number of B. treatae emerged/total number of galls/tree. Galls induced by early and delayed oviposition have the same maturation schedules and produce adult B. treatae that have similar emergence phenologies and survivorship in the presence of natural enemies. Thus B. treatae development is a plastic trait. However, survivorship, when exposed to natural enemies, differed significantly between early (x ± SE = 1.37 ± 1.29) and delayed (x ± SE = 20.99 ± 1.43) oviposition events. These results indicate that defoliation, as manipulated herein, created variation in oviposition timing but is not responsible for observed shifts between past and recent emergence phenologies. However, variation in oviposition timing, driven by defoliation can explain differences in survivorship in the presence of natural enemies. These results highlight the effects that common but patchy outbreaks of defoliators, driving variation in oviposition timing, can have on the timing of life cycle events and survivorship on this host specific phytophagous insect.
Assessing and maintaining genetic diversity is a concern for the conservation and management of a species, since variations within a species dictates the species evolutionary potential. The Reddish Egret is a relatively rare heron species that has a distinct white and dark plumage morph. Different regions within the Reddish Egret’s geographic range have different ratios of dark and white morphs. This may imply different microevolutionary processes affecting the frequency of the two morphs in different habitats and populations. I investigated how this phenotypical difference influences the behavior and reproductive ecology of the white and dark morph Reddish Egrets in the upper Laguna Madre of Texas. On dredge spoil islands in the Laguna Madre, Reddish Egret nesting pairs were observed at forty minute intervals as they courted, built nests, and raised young. I collected time-spent behavioral data, reproductive ecology information, and characterized vegetation of nests and the surrounding area. Regurgitant from chicks was collected opportunistically to determine differences in diversity and abundance of prey fed to young. Nest vigilance and nest initiation did not differ between morphs or nest sites, but nest attendance varied between morphs depending on nest site. Feeding time of chicks differed between morphs and is potentially related to foraging efficiency and time of day. Nest cover did not vary between morphs within sites, but varied significantly between sites and between random points and nests within sites. This indicates strong selection of nest sites within colonies. The information obtained provides valuable insights into the ecological diversity of polymorphic species, and information on nest site selection and prey diversity that could be considered for the conservation of this rare waterbird.
The dissertation proposal presented here describes a project which is an examination of the movement of organic matter and contaminants within and across aquatic-terrestrial interfaces in arid and semi-arid ecosystems. I will examine riverine organism utilization of terrestrial- and aquatic-derived organic matter (OM) along a climatic ecological gradient (arid to semi-arid landscapes) as well as determine the dominant OM sources for food webs along this environmental gradient. These patterns will be examined in small (order 1-2) streams and a large (order >6) river system in Texas (e.g., the lower Rio Grande and several of its tributaries).
Potential threats to springs are concerns because of their roles in water quality, indicators of pollution, and ultimately, geographic isolation. The discharge and relative permanence of springs currently is threatened by increased pumping of aquifers in locations proximate to or up gradient from the springs in west Texas (Porter et al. 2009). Because of the intrinsic value of springs in arid to semi-arid climates, a political solution needs to be achieved to balance human needs (i.e. water for livestock and irrigation) and ecological values.
Biofilms are the communities of bacteria encased within extracellular matrix which helps them to survive during adverse environmental situations. In the present study, we demonstrated that bacterial biofilms can act as a potential reservoir for largemouth bass virus (LMBV), a model eukaryotic virus which has no obligation to be associated with biofilms. LMBV, a member of family Iridoviridae is one of the naturally occurring fish viruses which cause fatal disease of largemouth bass (Micropterus salmoides) without any definite source of origin. Glass fibers were incubated with a mixture of different dilutions of LMBV stock of known titer and broth culture of Pseudomonas fluorescens ATCC13525, a naturally abundant bacterial strain. Using LMBV288F (5’-GCGGCCAACCAGTTTAACGCAA-3) and LMBV535R (5’-AGGACCCTAGCTCCTGCTTGAT-3’) primers, LMBV was detected in lab grown biofilms. Real Time PCR was able to quantify a maximum 6.22% of total LMBV in the adjacent bulk environment incorporated within biofilms following the SYBR Green method. The results also indicated that LMBV associated with lab grown biofilms is directly correlated to the LMBV concentration in the adjacent micro-environment. Real Time PCR could detect 100 fold less LMBV copy number than conventional PCR. Epifluorescent microscopy of biofilms grown in presence and absence of LMBV did not show any structural differences. The LMBV recovered from biofilms were further observed under transmission electron microscope (TEM) followed by negative staining by phosphotungstinic acid (PTA) and undergone a series of infectivity test following the TCID50 method. The later indicates that the LMBV isolated from biofilms are still infective. In a separate experiment, natural biofilm samples were collected from 4 different ponds of A. E. Wood Fish Hatchery, San Marcos, Texas; all of which were screened negative for LMBV by PCR. However, biofilm samples were positive when incubated with corresponding pond water spiked with LMBV stock. This study demonstrates the importance of examining microbial and ecological niches as potential reservoirs in the control of viral diseases. Similar experiments with other target viruses and host bacterial strains would determine if biofilms are reservoir for pathogenic viruses.
The sustainable use of the Rio Grande Basin is a continuing bi-national goal of Mexico and the United States. To address one major element of this goal – water quality issues associated with non-point source pollution (NPSP) – this research focused on two main objectives: (1) identifying critical areas in the Rio Grande Basin physically likely to generate NPSP, and (2) evaluating the effectiveness of different land management practices within critical areas to develop integrated solutions. To fulfill these objectives, a novel methodology integrating Geographic Information System (GIS) technology, a hydrologic model (Hydrological Simulation Program–Fortran, or HSPF), and social assessments, was developed and implemented.
Homogenization of the ichthyofauna of the United States is occurring in part as a result of introductions of nonnative fishes. Sport fishes are among the most widely introduced species in aquatic ecosystems and introgressive hybridization between introduced species and their native congeners has threatened many native sport fish species. The Guadalupe Bass, Micropterus treculii, is native to streams of the Texas Hill Country from the Brazos Drainage to the San Antonio Drainage. Introgression with introduced Smallmouth Bass, M. dolomieu, and degradation of stream habitats has lead to declines in Guadalupe Bass throughout its range. The purpose of this study is to 1) assess the introgressive status of Guadalupe Bass across its range using microsatellite and AFLP markers, 2) determine the population genetic structure of Guadalupe Bass using microsatellite, AFLP, and mitochondrial DNA markers to identify factors that have historically produced and presently affect this structure, and 3) test the hypothesis that populations with reduced genetic diversity associated with restorative stocking will also have narrower population niche widths and lower levels of individual level resource specialization by using stable isotope analysis. The results of this study will help to guide conservation and restoration efforts for Guadalupe Bass, elucidate mechanisms that have influenced the distribution and population genetic structure of aquatic species of the Texas Hill Country, and reveal the importance of genetic diversity to individual niche diversity at the population level.
Mercury (Hg) contamination of aquatic ecosystems is a global environmental problem and high levels of Hg can cause adverse health effects in humans and wildlife. Organisms at the base of the food web absorb methylmercury (MeHg) and this highly toxic and bioaccumulative form is passed onto fish and humans through their diets. While there is abundant data on Hg contamination and factors that affect Hg bioaccumulation in lake food webs, there is comparatively little data on large river systems. This thesis examines Hg concentrations of fish from the Lower Rio Grande drainage, Texas and several of its major tributaries in order to assess: (1) the overall level Hg contamination and potential risk to piscivorous organisms, (2) whether there is spatial variation in Hg concentrations in fishes of the lower Rio Grande drainage, and (3) if patterns of Hg contamination of Rio Grande fishes are related to abiotic and/or biotic factors that vary among sites (i.e., dissolved organic carbon (DOC), organic matter in sediments, and sulfates). We sampled fish at 15 sites from the Big Bend reach to the lower Rio Grande Valley and found that 56% of small-bodied trophic level 3+ fish had Hg concentrations exceeded EPA Wildlife Criteria (≥ 77 ppb). However, there was significant spatial variation in fish Hg concentrations with the highest concentrations found in the Big Bend reach. Principal Components Analysis revealed that fish Hg were positively related to river DOC, sediment total Hg, and sediment MeHg. Previous studies indicate that these factors are known to facilitate bacterial production of MeHg and its bioaccumulation. I hypothesize that high levels of inorganic Hg inputs to the Big Bend reach, such as runoff from abandoned cinnabar mines, Hg-rich rock formations, and atmospheric deposition from coal burning power plants in Mexico exacerbate Hg contamination of the fish community.
Maintaining adequate water supplies in the face of population growth and increasing urban development has been a serious issue in central Texas for decades. While traditional water resource management has focused on establishing a minimum standard of integrity for aquatic ecosystems, typically less emphasis is placed on the multi-scale linkages between human and ecological health, surface- and ground-water sources, ecological and economic well-being, and thus integrity of the linked riverine-terrestrial ecosystem as a whole. This recognition has led to increasing understanding of the need for systemic approaches that take into account the various biophysical, economic, legal, environmental, and other factors that impact the availability and use of water resources. The purpose of this study is to develop, through a participatory process, a decision support system (DSS) that will enable stakeholders and decision-makers to evaluate the impacts of management decisions in and around the Cypress Creek watershed, located in west central Hays County. A DSS incorporates both quantitative modeling and qualitative data to aid decision-makers in the integrated evaluation of management and policy impacts on both social and ecological aspects of a system. The DSS will take the form of linked surface- and ground-water flow models that capture the major processes affecting water quantity and quality in Cypress Creek, with additional analytical modules allowing for assessment of alternative management strategies given likely future scenarios. This study will develop scenarios that depict likely futures for the watershed, and analyze the impacts of these scenarios on water quantity, quality, and socio-economic factors identified by stakeholders. The impacts of the DSS development process on participants’ perceptions of problem structure, possible solutions, and model legitimacy will also be evaluated.
Biological invasions are significant components of human-caused global change, and invasive species pose major threats to rare and endangered native species and the integrity of native ecosystems. Cryptocoryne beckettii, native to Sri Lanka, has been reported from two sites in the United States: the Rainbow River in Florida, where it is an aggressive colonizer, and the San Marcos River in Texas. Cryptocoryne beckettii, a relatively recent introduction into the San Marcos River, represents a potential threat to habitat normally occupied by native aquatic plant species. Occurrence in shallow, rapidly flowing waters makes it a potentially serious threat to the endangered Zizania texana. Improved understanding of the characteristics of successful invaders and their interactions with natives will enable development of tools and management strategies to counteract both invasions and their negative impacts on ecosystems. Since C. beckettii has potential to become invasive, it is important to determine what characteristics it possesses that might contribute to its success as an invader. Objectives of this study are to confirm species taxonomy; determine the plant’s sexual and asexual reproductive capacity; determine extent of its competitive ability; and, determine community awareness, perceptions, and attitudes towards invasive species. Flowering will be induced in the laboratory and floral morphology used to verify correct taxonomy. The breeding system will be tested using hand pollination experiments. Asexual reproductive ability will be tested by conducting a series of growth treatments under laboratory conditions. An additional laboratory study will test competitive ability of C. beckettii with native and nonnative species. A survey administered to San Marcos River stakeholders will assess their perceptions of invasive species. This multifaceted body of research is critical for developing a framework for control of this invasive species in the San Marcos River and other aquatic ecosystems in the United States where it may become invasive.
This study focuses on a version of the historically popular approach called “integrated science and math.” Integrating science and math typically means making linkages between the two disciplines. Science uses math as a tool or way to teach science or math uses a science topic or phenomenon as an application of a math concept. The present study will evaluate a new instructional model of integrated science and math, Correlated Science and Math (CSM). This model is unique because the concepts in each discipline are taught with two fundamental goals: (1) acquisition by the learner of conceptual understanding of both science and math, not just as a tool or an example and (2) use each discipline’s proper language. Therefore, whether the lesson or course is science or math led, to be considered as using a CSM model both goals must be met. This study will evaluate certain components of the CSM professional development program especially designed for middle school science and math teachers. The study consisted of three cohorts of inservice teachers within the study time frame from the summer of 2006 to the spring of 2008. The mixed methods research design which has components of both qualitative and quantitative elements was used to explore the research questions. The data consisted of inservice teachers’ demographics including analysis of transcripts, certification and current teaching assignment; pre and posttests results; teacher evaluations of various components of the CSM program, and classroom observations. The data analyses suggested that the teachers acquired new knowledge in the science content areas more than in the math content areas, as a result of the CSM professional development program. The teachers gained a better understanding of CSM and were able to adopt either a CSM or integrated mode in the classroom.
Armored catfishes (Loricariidae), native to Central and South America, were introduced into North American waters through the aquarium trade, and became established in Texas waters in 1964. There is concern that breeding populations of these exotics could affect native species through dietary overlap, egg predation, and other factors. This study focused on two related topics: 1. the reproductive biology of Hypostomus in the San Marcos River, Texas; and 2. the potential effect of the foraging activities of the exotic on the egg survival of two native central Texas fishes (the endangered fountain darter, Etheostoma fonticola, and the threatened Devils River minnow, Dionda diaboli). Based on the oocyte diameters and estimated mean fecundity of the exotics (2,109), the Hypostomus population in the San Marcos River is reproducing as well in their new habitats as could be expected, and is not yet suffering from the effects of crowding. Photoperiod was the only environmental influen ce that could be associated with a peak in spawning activity, which occurred during the months of March through September. Size-frequency distribution plots of oocyte diameters from Ripe ovaries revealed two distinct modal diameters, suggesting a modified group-synchronous mode of ovarian development. Potentially deleterious effects of Hypostomus foraging on Devils River minnow and fountain darter eggs were assessed experimentally to evaluate the threat to these native species. The survival rate for fountain darter eggs was substantially lower when exposed to foraging Hypostomus, and three whole eggs were found in the digestive tract of the two experimental Hypostomus. These findings suggest that the exotic is positively trophotaxic toward fountain darter eggs, and may substantially reduce the breeding success of the darter in shared habitats. In contrast, egg survival rates for the Devils River minnow were only slightly lowered by foraging Hypostomus, and no eggs were re covered from the digestive tract.
For the past three decades North American grassland birds have been on the decline. Loss of habitat from urbanization, agricultural land use, and encroachment of woody species may account for this decline. One method of restoring remnants of grassland habitat is prescribed burning, typically performed in wet, cool periods when fire behavior is more benign. Fires historically helped in maintaining grasslands by suppressing woody plants and encouraging herbaceous growth; however, the majority of these natural fires occurred in the summer growing season. To determine if this shift in burn season affects avian forage, I looked at avian species foraging on summer, fall and winter burns plus unburned control plots over a year. The results indicated no difference in avian species use of these different burn treatments for forage. Future studies should investigate how changes in vegetation on different seasonal burns influence avian foraging. My results did show that managing grassla nds with prescribed burns in dormant periods would not negatively affect grassland bird species.
The phyto-hormone auxin is vital for the plant growth and development throughout its lifecycle. At molecular level, auxin rapidly modulates the expression of auxin responsive genes by degrading a family of negative regulators known as Aux/IAA proteins. Besides the major natural auxin Indoleacetic acid (IAA), there are several other natural and many synthetic auxins. Picloram and 2,4-dichlorophenoxyacetic acid (2,4-D) are two such synthetic auxins that are commonly used as herbicides. Our initial results suggest that picloram may functions somewhat differently from other commonly used auxins such as IAA, 2, 4-D and 1-NAA.
Abstract. The Texas tortoise (Gopherus berlandieri) is a state threatened species in Texas. Expanding agricultural practices and urban development are the major causes of habit degradation for G. berlandieri. However, the need to develop a range wide management plan for this species has rarely been discussed. In order to provide further information for future management planning for this tortoise, the existing genetic variability, population structure and its history within the U.S. species range were examined. We hypothesized geographic distribution of genetic diversity being shaped by the Nueces River basin that bisects the species range. We used 11 microsatellite loci for 127 individuals across nine sampling sites. Statistical analyses indicate moderate genetic diversity in G. berlandieri and some evidence of genetic differentiation into northern and southern populations separated at the south of Duval County. The weak population structure detected is probably as a result of ongoing gene flow. The relationship between the population structure and the Nueces River basin was not clear, necessitating further investigation to evaluate the current and alternative hypotheses. We recommend a conservative approach of population management by treating the two populations as separate management units. We strongly feel that cooperative effort by the state and private stakeholders is necessary to initiate range wide management of this diminishing tortoise.
Substantial commercial harvesting of wild freshwater turtles has occurred in the lower Rio Grande Valley of Texas since the 1990s. State regulations were created in 2007 to eliminate turtle harvesting in public waters, while common turtle species have no harvest protection in private waters. In addition to harvest, road mortality may be increasing due to extensive human population growth since the 1970s. I repeated a study conducted in 1976 to determine if demographic changes have occurred in freshwater turtle populations over the last three decades. Original trapping locations were re-located and when possible re-trapped with similar trapping effort using baited hoop nets. Species, sex, carapace length and width, plastron length and width, body depth, and weight were recorded for individual turtles. Data were analyzed for red-eared slider (Trachemys scripta elegans) and Texas spiny softshell (Apalone spinifera emoryi) captures. Capture-rates and carapace lengths were compared using unequal variance t-tests or randomization tests, adult sex-ratios were compared using Chi-square goodness-of-fit tests, and correlations between red-eared slider carapace lengths and roads were tested using Spearman Rank Correlation Coefficient tests. The mean red-eared slider capture-rate was significantly lower in 2008. Mean male and female red-eared slider carapace lengths were significantly longer in 2008. Red-eared slider adult sex-ratios were typically more male-biased in 2008. The mean female Texas spiny softshell carapace length was significantly longer in 2008, and the adult sex-ratio was significantly more male-biased. A significant positive weak correlation was detected for female red-eared slider carapace lengths and road density within 1 km and 5 km of trapping locations. The changes detected cannot be attributed solely to harvest. They are likely the result of several factors including harvest, differential mortality, changes in habitat availability, and natural fluctuations.
As Texas Hill Country communities continue to experience rapid growth, the Pedernales River Watershed faces increased human pressure and demands on its ecological services. The Texas Water Development Board (TWDB) projects that the population of the two principle counties, that comprise the majority of the Pedernales River Watershed (Gillespie and Blanco Counties) will have a combined increase of about 62% from 2000 to 2060. Combined water demand, for Gillespie County and Blanco County, is expected to increase by 25%. Though, increased demand for water resources pose a more obvious threat to fluvial ecosystems, changes in land cover associated with increased population may pose a more severe threat. Several studies have identified human manipulation of land cover in the contributing watershed as profoundly affecting riverine systems. P. Molnar recently noted that a vision of river management relative to the watershed is critical for the evaluation of conservation projects and potential anthropogenic impacts. Many water resources managers are beginning to broaden their views concerning landscape change and its effects on river systems, since land use and land cover changes at the watershed scale are the primary ways that humans affect water resources and aquatic ecosystems.
The Comal Springs Riffle Beetle, Heterelmis comalensis, is an endangered endemic species, occurring in only two spring complexes in the Texas Hill Country, Comal Springs and San Marcos Springs. I surveyed molecular genetic variation in H. comalensis and three congeners from Texas using mitochondrial and nuclear sequence markers and amplified fragment length polymorphisms (AFLPs), to determine whether H. comalensis is experiencing reduced genetic variability within and among populations in its limited geographic range, and to determine evolutionarily significant units (ESU)s for the species. Additionally, a morphological analysis of a cri tical character for distinguishing Heterelmis species in the current taxonomic key was conducted, and was used to assess the concordance between the characters used to delineate Heterelmis species and the patterns of molecular genetic variation found within and among them. Mitochondrial DNA (mtDNA) analyses revealed a surprising amount of genetic variation within and differentiation among three of the seven H. comalensis populations sampled, specifically when compared to the common flight- and drift-dispersed species of Heterelmis, suggesting isolation among populations, with little to no current gene flow. However, sequencing of the single-copy nuclear gene ITS revealed a single haplotype within H. comalensis and its most closely related congener, suggesting recent divergence of the two species. Partially supporting mtDNA results, AFLP analyses clustered the H. comalensis population into two groups, those with high and those with low genetic diversity. Finally, this study f ound that nominal species designations using the current taxonomic key are incongruent with morphological and molecular data, necessitating amendment to the key. Genetic variation is exceptionally high in three of the H. comalensis populations. However, common summer droughts in Texas in combination with human withdrawal of water threaten the springs that H. comalensis inhabit, and may have caused severe population bottlenecks in the four remaining (invariant) populations.
As the concern for potentially declining biodiversity grows, it is increasingly necessary for environmental management decisions to be made on the local scale, often with limited data. It is imperative to have a good mechanistic understanding of local processes and how they affect biodiversity as well as a readily available, widespread data source. Variation in local plant diversity can be a result of differences in alpha or beta diversity. Alpha or within-habitat diversity is increased by processes that slow or stop competitive exclusion within a relatively homogeneous area. Beta or between-habitat diversity increases in areas with greater environmental heterogeneity which creates habitat patches with differing conditions and species mixtures. Differences in local resources between habitat patches can facilitate coexistence of plant species through increased beta diversity. Topography and climate are easily described with remote sensing and each can create heterogeneous moisture conditions across a landscape. My emphasis however, will be on the interaction between topographic heterogeneity and local climate. I hypothesize that over the same topography, differences in precipitation can create a wide range of soil moisture heterogeneity with the most “effective heterogeneity” for promoting high plant diversity occurring at moderate levels of aridity. The proposed studies will explore the relationship between plant species diversity, specifically the beta component, and “effective heterogeneity” of moisture gradients in different environments. A computer model will be used to test the topography/climate interaction mechanisms that generate “effective heterogeneity”. Field data collected in a hierarchical format will be used to compare the relationship between “effective heterogeneity” and plant beta diversity across spatial scales and through time. Analysis of remotely sensed data will be compared to field data and if consistent will be a potentially powerful tool to explain geographic patterns of plant species diversity. If a generalized mechanistic relationship between environmental heterogeneity and species diversity can be shown, then local land management will be able to more effectively buffer against potential species loss. Current and future high-resolution environmental data from remote sensing can be used to more accurately estimate the local species richness of unknown areas and improve predictions of the effects of land use change.
Turtle eggs and embryos may succumb to a variety of causes of mortality, including vertebrate and invertebrate predators. Characteristics of nest sites selected by turtles may influence survival of offspring. Spring Lake in San Marcos, Hays County, Texas supports several native, non-native, and endangered species. It also serves as an educational and recreational area. This study investigated the survival and causes of mortality of the eggs of Texas river cooters (Pseudemys texana) and red-eared sliders (Trachemys scripta elegans) at Spring Lake. A total of 122 nests were monitored during the 2006 and 2007 nesting seasons. Random nests were protected from vertebrate predators and excavated approximately 70 days after oviposition to determine hatchling success, while others were not protected from predation. Combined data from both years reflected a 59.21% (n = 45) predation rate by raccoons on unprotected nests. After excavation, 45.65% (n = 21) of protected nests yielded live hatchlings, 45.65% (n = 21) were unsuccessful, and 8.7% (n = 4) were false nests. Protected nests that were unsuccessful were a result of excessive water (rainfall), desiccation, or various other causes including incomplete development and ants. Six parameters (distance from water, distance from nearest tree, distance from nearest man-made structure, substrate, slope, direction of slope in relation to water, and canopy cover) were recorded from 60 nest sites and 60 random non-nest sites. A MANOVA of these data suggested that nest-site selection did occur (P < 0.0001). Principal Components Analysis (PCA) suggested that distance from water was the principal component in nest-site selection. These data suggest that raccoon predation and moisture-related factors are the primary causes of mortality of turtle nests at Spring Lake.
Exotic ruminants were introduced into Texas with little knowledge of how the species would interact with native white-tailed deer (Odocoileus virginianus). Axis deer
Turtle eggs and embryos may succumb to a variety of causes of mortality, including vertebrate and invertebrate predators. Characteristics of nest sites selected by turtles may influence survival of offspring. Spring Lake in San Marcos, Hays County, Texas supports several native, non-native, and endangered species. It also serves as an educational and recreational area. This study investigated the survival and causes of mortality of the eggs of Texas river cooters (Pseudemys texana) and red-eared sliders (Trachemys scripta elegans) at Spring Lake. A total of 122 nests were monitored during the 2006 and 2007 nesting seasons. Random nests were protected from vertebrate predators and excavated approximately 70 days after oviposition to determine hatchling success, while others were not protected from predation. Combined data from both years reflected a 59.21% (n = 45) predation rate by raccoons on unprotected nests. After excavation, 45.65% (n = 21) of protected nests yielded live hatchlings, 45.65% (n = 21) were unsuccessful, and 8.7% (n = 4) were false nests. Protected nests that were unsuccessful were a result of excessive water (rainfall), desiccation, or various other causes including incomplete development and ants. Six parameters (distance from water, distance from nearest tree, distance from nearest man-made structure, substrate, slope, direction of slope in relation to water, and canopy cover) were recorded from 60 nest sites and 60 random non-nest sites. A MANOVA of these data suggested that nest-site selection did occur (P < 0.0001). Principal Components Analysis (PCA) suggested that distance from water was the principal component in nest-site selection. These data suggest that raccoon predation and moisture-related factors are the primary causes of mortality of turtle nests at Spring Lake.
Exotic ruminants were introduced into Texas with little knowledge of how the species would interact with native white-tailed deer (Odocoileus virginianus). Axis deer
The Red-tailed Hawk (Buteo jamaicensis) is a species that has shown a positive ability to adapt and populate urbanized environments in some U.S. cities while displaying a negative ability to adapt in others. The purpose of this study was to determine if Red-tailed Hawk occupancy was affected by differing characteristics of urbanization along roadway corridors in Austin, Texas.
The Red-tailed Hawk (Buteo jamaicensis) is a species that has shown a positive ability to adapt and populate urbanized environments in some U.S. cities while displaying a negative ability to adapt in others. The purpose of this study was to determine if Red-tailed Hawk occupancy was affected by differing characteristics of urbanization along roadway corridors in Austin, Texas.
Reproductive isolation restricts genetic exchange between species. Various pre- and post- mating barriers, such as behavior, physiology and gametic incompatibility, have been shown to evolve in sympatry. In certain scenarios, isolation can be asymmetrical, where species differentially prefer conspecifics. We examined reproductive isolation from a behavioral and physiological standpoint in both sexes of Gambusia affinis and Gambusia geiseri. These species are sympatric in various river systems in Texas. To investigate male contribution to reproductive isolation, we compared number of gonopodial thrusts directed at either a conspecific or a heterospecific female, in both species. We then measured female association preference for either a conspecific or heterospecific male, in both species. Lastly, we examined sperm priming and expenditure in males in the presence of conspecific or heterospecific females. We found that males thrust more at conspecific females in both species. Females, of both species however, did not associate more with conspecific or heterospecific males. In our final experiment, males in either species did not prime or expend more sperm for either species of female. These results suggest that reproductive isolation is mediated by male mate choice in this system and not female choice, suggesting that there is asymmetrical isolation between the sexes in G. affinis and G. geiseri, however, species isolation is symmetrical.
Spinal cord injuries and neurodegenerative diseases in mammals result in a loss of function due to the failure of neurons in the central nervous system (CNS) to survive and regenerate their axons. Unlike mammals, fish and amphibians possess the ability to regenerate their CNS following damage. To gain a better understanding of the factors necessary for successful CNS regeneration, I conducted a temporal analysis of the changes in gene expression in the retina caused by optic nerve injury to identify genes specifically involved in regeneration. Dual color oligo-nucleotide microarrays and subsequent confirmation by qRT-PCR was used to compare total RNA from retinas of sham and optic nerve injured fish at 3, 24 and 168 hours. Statistical analyses identified 722 genes differentially expressed by at least 1.5-fold in one or more time points, and 142 genes with at least a 2.0-fold difference. Gene ontology analysis indicated genes expressed at the earlier time points (3 hours and 24 hours) included hox genes, transcription factors, genes involved in chromatin remodeling and developmental pathways such as Wnt, BMP, and Notch signaling pathways. Genes expressed at the later time point (168 hours) correspond to transcription factors, protein metabolism, cytoskeleton, and cell metabolism. These results confirm that differential gene expression analysis can provide insight into process of CNS regeneration. The mechanisms governing optic nerve regeneration are complex and may require the partial reactivation of developmental pathways for successful axon growth and re-enervation.
Bothriocephalus acheilognathi is native to Asia and was introduced worldwide as an incidental hitchhiker of its native host, Ctenopharyngodon idella. It is established in ten states in USA with the most recent discovery in the Rio Grande in Texas. Occurrence of this exotic tapeworm in the Rio Grande potentially is detrimental to native fishes, causing intestinal blockage and perforation, hemorrhaging, reduced growth, significantly decreased survivorship, and mortality. Endemic fishes of conservation concern in the Rio Grande include Hybognathus amarus, Dionda diaboli, Notropis jemezanus, and Notropis chihuahua and likely are affected by the tapeworm.
Little is known about resource selection patterns of scimitarhorned oryx (Oryx dammah) in Texas, information that is vital for informed management decisions. Scimitarhorned oryx are less dimorphic in body size (males approximately 12% larger than females) than most ruminants (males 20 50% larger than females). Ruminants dimorphic in body size display intersexual differences in diet and spatial patterns, presumably because of body size differences. Consequently, scimitar-horned oryx is an ideal species to test for intersexual differences in spatial patterns, diet and food selection. I hypothesized that male and female scimitar-horned oryx associate in mixed-sex groups and do not exhibit intersexual differences in forage selection. My study was initiated in June 2006 at Mason Mountain Wildlife Management Area in central Texas and was completed in April 2007. In six different months, I measured grouping patterns from systematic vehicle surveys conducted at dawn and evening, observed males and females through binoculars and collected fecal samples from known sex individuals. I determined food habits by identifying plant fragments in fecal samples. Forage availability was measured seasonally by establishing 100 m transects in areas where fecal samples were collected. Mixed-sex groups were encountered more frequently than any other group type and ≥ 69 percent of males and females encountered were in mixed-sex groups. There were no differences between the diet of males and females. Scimitar-horned oryx displayed differences among months in forage selection but the majority of the diet was grasses. Findings of this study support expectations based on body size, males and females occur in the same groups and consume similar forages. Unlike many ruminants, managers do not have to consider separate habitat requirements of each sex when managing scimitar-horned oryx.
Mercury is a global pollutant and organic forms are known to bioaccumulate in aquatic ecosystems. There is a paucity of data on the behavior of mercury in subtropical reservoirs, often because they are distant from emission or other pollution sources. Sediments and muscle tissue of the popular sport fish, largemouth bass (Micropterus salmoides), from Amistad International Reservoir, TX, were analyzed for concentrations of total mercury, organic methylmercury, and other environmental and biological factors known to influence the production and bioaccumulation of methylmercury. The Rio Grande arm of the reservoir had the highest sediment concentrations of total mercury, but below the TCEQ 100 ng/g sediment screening level. However, the concentration of methylmercury, which is problematic at much lower levels, was highest at sites in the Pecos River and Devils River arm (5.02 and 3.90 ng/g, respectively). Conditions in the sediments of the Pecos and Devils Rivers appeared to be more favorable to the production of methylmercury, with higher sediment porewater dissolved organic carbon, porewater sulfate levels in the optimum range for mercury methylation, and a higher number of detections for sulfate reducing bacteria, the microbial group most highly correlated with methylmercury production. A composite sample of 55 fish of legal sport fishing size had over 50% exceeding the 0.47 mg/kg threshold corresponding to a recommended consumption limit of no more than one meal per month. Additionally, fish at a standardized length of 18.5 cm from the Devils River and San Pedro Canyon areas of the reservoir had higher muscle concentrations of mercury than those collected in the Rio Grande arm, suggesting higher rates of bioaccumulation in the DevilÂs River arm. This highlights the need for a better understanding of the spatial dynamics of mercury in the reservoirs of the arid west and southwest of the U.S.
The cricket frogs (genus Acris) consist of two species of small anuran with a combined distribution that spans much of the eastern two thirds of North America. Of these two species, only the northern cricket frog, Acris crepitans, is known to occur in Texas. Previous research has demonstrated significant variation among subspecies of Texas Acris crepitans in male advertisement calls and in female preferences for call properties, which suggests the potential for prezygotic reproductive isolation. This research investigated geographic variation in spectral and temporal properties of the male advertisement call and a series of morphological characters from three adjacent Central Texas river basins (Brazos, Colorado, Guadalupe). Specifically, this research asked whether significant variation in morphological and behavioral characters is detectable at a small geographic scale, and whether covariation of suites of characters exhibits any geographic pattern. Van der Waerden non-parametric analysis of variance was used to assess geographic variation in individual call and morphological characters. For characters having significant ANOVA results, a Tukey-Kramer HSD was used to identify pairwise differences. All characters having significant ANOVA results were analyzed in a Principal Component Analysis (PCA) to assess geographic patterns of covariation among characters. Three advertisement call variables, four linear morphologic variables, and three morphometiric ratios had significant ANOVA results, though pairwise differences did not exhibit a clear geographic pattern of variation. However, PCA using these ten variables revealed that the Brazos population was distinct from the other two. The results of this analysis suggest that a recent subspecific revision in Acris crepitans bears further scrutiny, and that broad-scale multivariate analyses, including population genetic data, are needed to better understand the evolutionary history of this genus.
Previous research in pelagic ecosystems suggests that nutrient sequestration and carbon flow through heterotrophic bacteria is relatively high in oligotrophic systems but decreases as trophic state increases. I assessed this hypothesis and mechanistic explanations in 17 reservoirs in Texas and Ohio, USA. I measured bacterial production (BPr), primary production (PPr), planktonic nutrients, dissolved organic carbon (DOC), soluble reactive phosphorus (SRP), and dissolved inorganic nitrogen (DIN). The % of planktonic carbon (C), nitrogen (N), and phosphorus (P) in the bacterial size fraction (< 1-μm) was highest in oligotrophic reservoirs but decreased as trophic state increased. Comparison of planktonic nutrient data to Minnesota natural lakes suggests a similarity in nutrient sequestration by bacteria in reservoirs and natural lakes. BPr and PPr ranged from 17 ÃÂ 172 and from 41 ÃÂ 1,695 μg C L-1 d-1, respectively. BPr:PPr decreased as our measure of trophic state, chlorophyll, increased (r2 = 0.42). DOC, DOC:SRP, and DOC:DIN did not improve predictions of BPr:PPr over that based solely upon chlorophyll. These variables may have limited use as predictors of BPr:PPr across a broad range of trophic state. BPr:PPr was better predicted by DOC:planktonic carbon (PC) (r2 = 0.47) and mixing depth (Zmix) (r2 = 0.61) than by chlorophyll. However, the relationship between BPr:PPr and DOC:PC was primarily driven by the relationship between BPr:PPr and PC (r2 = 0.41), which was a surrogate for trophic state. Unexpectedly, the strength of Zmix as a predictor BPr:PPr did not primarily reflect differences in the light environment. My results support the hypothesis that the relative importance of heterotrophic bacteria is highest in oligotrophic systems and decreases as trophic state increases, but I found limited support for several of the proposed mechanisms of this pattern. My results suggest that patterns in microbial dynamics are similar in reservoirs and natural lakes.
Woody encroachment is the uncontrolled expansion of woody plants into grasslands and open savannas, with usually negative consequences for rangeland productivity and water resources. It is a worldwide phenomenon, but there are interesting regional differences in the identity and ecophysiology of woody encroachers. For instance, large portions of west to central Texas, including the Blackland Prairie (BP), are currently encroached by deep-rooted honey mesquite (Prosopis glandulosa). However, across the Balcones Escarpment, on the eastern Edwards Plateau (EP) of Texas, honey mesquite is almost entirely excluded and Ashe juniper (Juniperus ashei) is the dominant woody encroacher. I ask if species differences in their responses to soil depth are responsible for this biogeographical pattern. I will test the hypotheses that 1) the limited soil depth of the eastern EP poses a water relations problem for mesquite but not for juniper, especially during periodic drought conditions and that 2) the deeper soil profile of the BP provides additional soil moisture for mesquite that is not available to juniper. I will try to establish that differences in the root development of the two species drive these patterns, such that mesquite is unable to develop sufficiently deep roots on the shallow soils of the EP to support adequate levels of gas exchange, whereas, juniper roots on the deep BP soils remain shallow and this results in an increase in drought sensitivity. I expect that the results of this study will inform land management by providing information about species- and site-specific constraints on the water consumption of woody encroachers.
The once mighty Rio Grande has become one of the most challenged river systems in North America, and has been included in a list of the 10 rivers most at risk globally. The use of the river by native species, as well as the status and structure of their current populations relative to historic populations, is critical for management and conservation of all species native to the Rio Grande. To examine the effects of both ancient and modern changes on taxa native to the Rio Grande, two river-dependant species were chosen, Trachemys gaigeae (Big Bend Slider) and Pylodictus olivaris (Flathead Catfish). T. gaigeae is on the IUCN red list, and has apparently been extirpated from most of its historic range in the Rio Grande. This species is also facing competition and hybridization with introduced individuals of its sister taxa, Trachemys scripta elegans (Red eared slider). Anecdotal reports have suggested that the distribution of P. olivaris has changed as well. Both mitochondrial DNA and nuclear microsatellite markers are being employed to examine these issues. Preliminary results of mitochondrial data from Trachemys have shown that hybridization is indeed occurring in populations in Big Bend National Park. Preliminary microsatellite analysis results for Trachemys have shown that while there was once gene flow between New Mexico and Texas populations, they are now strongly differentiated (Fst=0.295). Microsatellite data also suggests hybridization, viability of hybrids, and supports the introduced origin of T. s. elegans in Big Bend National Park. Preliminary mark-recapture data for T. gaigeae has demonstrated that the species has a greater than anticipated ability for long-range dispersal. Patterns of population structure and history will be compared between the two species, to determine if concordant patterns exist suggesting recent changes to the river are having similar effects on species with differing life histories.
I investigated the feeding habits of wild northern bobwhites (Colinus virginianus) harvested from the Chaparral Wildlife Management Area, south Texas, in October 2004 and January 2005. The CWMA is a 6,151 hectare ranch located in the Rio Grande plains ecological region of Texas that is characterized by thorny brush such as mesquite (Prosopsis glandulosa), acacia (Acacia sp), and prickly pear (Opuntia sp). The contents of 200 crops were dried, sorted, and weighed to the nearest .0001 gram. Percent dry weight was used to assess differences between season harvested, sex, and age. The fall diet consisted of about 76% seeds, with 64 species represented. Queen's Delight (Stillingia sylvatica), Woolly croton (Croton capitatus), and Browntop signalgrass (Urochloa fusca) represented greater than 50% by weight of seeds found in the fall diet. Fruit, almost entirely Spiny hackberry (Celtis ehrenbergiana), represented 17% of the fall diet. Invertebrates made up about 5% and green vegetative matter contributed 0.1% of the fall diet. No differences in feeding habits between sexes or age class were detected for fall. The winter diet consisted of 63% green vegetative matter, 28% seeds, 5% invertebrates, and 0.40% fruit. Common yellow Oxalis (Oxalis stricta) and a species of pellitory (Parietaria sp) made up over 50% of the green vegetative matter found in winter crops. Percent green vegetation (78%) consumed by females exceeded (F(1,96) = 4.727, P = 0.032) that consumed by males (53%) in winter and seeds consumed by males (40%) exceeded (F(1,96) = 4.799, P = 0.031) that of females (12%). Additionally, in winter green vegetation consumed by adults (70%) exceeded (F(1,96) = 5.726, P = 0.019) that of juveniles (59%). Differences by sex in the winter diet might be due to differences in nutritional requirements in the pre-breeding period.
Native bottomland pecan (Carya illinoiensis) communities exist as fragments along river systems of the Edwards Plateau. They persist in this sub-humid rangeland environment because of the unique hydrologic regime of the riparian zone. Bottomland sites are currently dominated by an over story of mature pecan trees with little woody understory or replacement pecan seedlings. The lack of pecan recruitment might result in the loss of these native bottomland pecan communities as adult trees senesce and die. Objectives of my study were to: 1) determine the extent of change in these communities over several decades, 2) assess current age structure of these communities, 3) assess impact to recruitment due to herbivory and grove management, and 4) construct a computer-based conceptual model of community behavior to identify factors having the potential to affect native pecan bottomlands. Sites were selected based on species composition, accessibility, herbivore pressure, and management history (natural, harvested, harvested/groomed). Twenty pecan trees from each site were cored and cores were sent to a dendrochronology lab for aging. Results show that these pecan communities have changed little in size over the past 60 years. These communities exist primarily as mature trees with few younger age classes. Deer densities are extremely high within these communities indicating that herbivory is likely influencing recruitment rates. Computer simulation modeling identified factors affecting recruitment and mortality of native pecan trees in bottomland communities.
Abundance and distribution of species tend to be linked, so when outside forces cause changes in population size there is also a change in the number of sites they occupy. Presence-absence surveys are a simple method to monitor these changes and give valuable information on avian assemblages facing development and changing land use practices, and have been argued to be more accurate than point counts. The need for reliable and cost-effective surveys is a constant challenge for biologists. Outside agencies or organizations may be an answer to this problem. Landowners in Texas may perform bird censuses as one of the requirements to maintain their agricultural tax status by managing for wildlife. These data are public information and might be used to track broad-scale changes across an area through time. Using Coefficient of Jaccard, I found that the landowner surveys had a 51% similarity to presence-absence surveys I conducted in all seasons, and 56% similarity to my spring and summer data. Common, year-round species such as Northern Cardinal (ψ = 0.9958, p = 0.7229) and Carolina Chickadee (ψ = 1.00, p = 0.5580) had high occupancy and high probabilities of detection and were detected on landowner surveys. Secretive species, such as the Yellow-billed Cuckoo (ψ = 1.00, p = 0.1017) had low probabilities of detection but were also detected by landowner surveys. Twelve species were equally detectable and year-round residents. Occupants whose occupancy varied seasonally (n=7) all declined from spring to winter, except for the Eastern Phoebe. Two species varied in occupancy and detectability seasonally but only the Eastern Phoebe increased from spring to winter. All but four of these species were detected on landowner surveys. Data suggests that landowner and contractor surveys can be used by biologists to track changes at a broad-scale, such as a river valley, through time.
Habitat loss, through urbanization and habitat degradation, is a major component threatening endangered Black-capped Vireo populations. Acquisition and management of breeding habitat are identified as the main objectives for recovering populations to a viable level. In order to identify attributes of suitable habitat for Black-capped Vireos, it is essential to understand the way they use their habitat. I examined Black-capped Vireo foraging behavior for adults and fledglings and identified differences that existed between the sexes at four study sites in Central Texas. G-test of Independence and Fisher's Exact test were used to compare frequency distributions of males and females for foraging height, height of tree used, tree species, substrate and foraging maneuvers. I found males and females foraged at different proportions relative to various height classes with males foraging at all levels but primarily greater than 3 m and females foraging almost exclusively below 3 m. Males used taller vegetation proportionally more than females, which consequently, influenced the use of different tree species. No intersexual difference was found for substrate and maneuvers during foraging attempts. All Black-capped Vireos primarily gleaned from foliage. Fledglings foraged generally below 2 m but were observed using vegetation >3 m 50% of the time. Due to the use of tree canopies for foraging by males and taller vegetation by fledglings, greater vertical strata may be an important component commonly overlooked when identifying a heterogeneous landscape for Black-capped Vireos. Additional fledgling dispersal studies are recommended to identify detailed fledgling habitat use prior to migration.
Introduced suckermouth catfishes (Family Loricariidae) are established in a number of spring-influenced streams in North America. Impacts to native flora and fauna are predicted, but these predictions have not been tested. Purposes of this study were to quantify gut contents of suckermouth catfishes from the San Marcos River in central Texas and to assess degree of dietary overlap between the suckermouth catfish and native herbivorous fishes by comparing gut contents and through stable isotope analysis. Suckermouth catfishes (N = 36) primarily consumed amorphous detritus (87% in biovolume), filamentous red algae (5.4%), and picoplankton (4.1%). Stable isotopes analysis indicated a more omnivorous trophic level. An endangered macrophyte, macroinvertebrates, and fish eggs were not found in the gut contents. Suckermouth catfish gut contents were similar (P >0.05) to those of a sympatric native herbivore, Guadalupe roundnose minnow Dionda nigrotaeniata, but differed (P <0.01) from another sympatric native herbivore, central stoneroller Campostoma anomalum. Gut content assessments of two additional Dionda species suggest high dietary overlap between the Dionda complex and suckermouth catfish. Consequently, occurrences of suckermouth catfishes in spring-influenced streams are potential direct competitors with native taxa in spring-influenced streams of central and west Texas.
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.
Recreational human activities along waterways may influence the abundance of waterbirds. I investigated the possible impacts of recreational activity and vegetative characteristics on the relative abundance of waterbirds along a heavily used river, the San Marcos River, in central Texas. Abundance of waterbirds and human disturbance was estimated by conducting point counts for 20 minutes at 30 randomly determined locations along the San Marcos River. Measurement of riparian characteristics at representative transects along the San Marcos River system were conducted to examine correlations between certain vegetative and aquatic parameters and bird abundance using multi-variant statistics. A Principle Component Analysis test was run to analyze the difference between the three a priori sections of the river, divided by the amount of disturbance present, as well as variance partitioning, a test utilizing the Canonical Correspondence Analysis test. With only 2 percent of the explained variation in the location and abundance of waterbirds coming from human disturbance, out of 25 percent explained in total, its apparent that the birds may have habituated out of necessity and that the river vegetative composition is the major deciding factor in determining bird abundance.
Myotis velifer is known to exhibit a wide-range of geographically correlated morphological and behavioral variation, reflecting genetically unexplored ecological subdivisions. Unlike migratory chiropterans, genetic structure is generally found among chiropterans exhibiting non-migratory behavior. Interestingly, both migratory and non-migratory behavior is noted among M. velifer. Morphometric analyses proposed existing barriers to gene flow among taxonomic subdivisions. Furthermore, abandonment of historical roosts has been a primary contributor for the species of concern designation throughout Texas. Genetic methods were used to evaluate whether population genetic structure is congruent with behavioral or taxonomic subdivisions and, assuming a decline is associated with roost abandonment, whether a population decline in Texas is the result of a history of demographic contraction. To explore these proposals and concerns, tissue samples were collected from roosts in the Texas Panhandle (3), central and west Texas (13) and the California-Arizona border (4), representing both behavioral groupings and three taxonomic subdivisions. Mitochondrial sequence data (982 base pairs of Cytochrome b) from 104 individuals recovers 54 haplotypes and three haplogroups. Thirty-four microsatellite loci evaluated for cross-species amplification yielded four suitably polymorphic autosomal loci and one X-linked locus. Mitochondrial structure is not congruent with behavior, taxonomy, or geography and microsatellite data (n = 192) recovers no genetic structure. Mitochondrial data indicate weak regional fidelity, nuclear data indicate substantial gene flow, and demographic analyses indicate historic demographic expansion among M. velifer. The current subspecies of M. velifer are not genetically supported; however, considering morphological and behavioral data M. v. magnamolaris should be maintained whereas California specimens should be grouped with M. v. incautus. Analysis of Mexican and Central American specimens is needed to determine support for a third subspecies. Management of the two proposed subspecies should be across areas containing multiple roosts until conclusive evidence suggests causes of roost abandonment.
ABSTRACT
Actinorhizal plants are characterized by their ability to form root nodules in symbiosis with the nitrogen-fixing bacterium Frankia which enables them to grow on sites with restricted nitrogen availability. They are therefore uniquely successful pioneer plants, frequently establishing themselves after environmental disturbances, but have also potential for use in forestry, e.g., as nurse trees in mixed plantations with valuable tree species. The establishment and success of the symbiosis depends on environmental conditions, but is ultimately determined by the genotypes of both partners of this symbiosis. Since very little is known about the fate of Frankia strains -introduced or indigenous- in soil, the basic objective of this Ph.D. study is to elucidate the effects of specific environmental factors, i.e., different carbon resources on the fate and nodule-forming capacity of Frankia populations in soil. We hypothesized that strains differ with respect to their ability to utilize specific organic compounds, that the utilization of complex organic matter in addition to root exudates is a specific trait of few Frankia strains, and reflected in their taxonomic position, and that amendments with specific carbon resources affect Frankia community structure in soil, with consequences for their nodule forming capacity.
Canopy strata of tropical forests are one of the remaining unexplored biotic frontiers. New access techniques to the canopy have facilitated an increased investigation on the ecology of forest canopies and their function in tropical ecosystems. As the interface between the terrestrial environment and atmosphere, the canopy and its inhabitants are integral to ecosystem function and maintenance. Epiphytes, tank bromeliads in particular, provide microhabitat for a high diversity of fauna and flora in tropical forest canopies and are considered a "keystone resource". A number of amphibians inhabit these phytotelmata yet their ecological role in forest canopies remains primarily unknown, while knowledge of arthropods has increased significantly in recent years. Anthropogenic perturbations are rapidly altering the landscape of the Ecuadorian Amazon and along with it the species diversity, forest dynamics, and ecosystem functions. The proposed study will investigate the symbiotic relationship of tank bromeliads and their inhabitants, the influence of forest management regimes on this relationship, impact of human disturbance on their status in the ecosystem, and the phylogenetic divergence of terrestrial and canopy dwelling amphibian congeners. Resulting data provide science-based support to promote social responsibility and conservation efforts throughout Amazonia.
Ecological assessments commonly focus on the measurement of biological, chemical, and/or physical properties in order to determine the health of an ecosystem. One important consideration often left out of the assessment is an evaluation of the laws and policies, as enacted by humans, which affect the conservation, preservation, or development of that ecosystem. Without such considerations, healthy and diverse ecosystems may still be vulnerable to human induced perturbation, such as the development, consumption, or exploitation of the resources within the system. The objective of this research is to develop a socio-political component to augment traditional ecological assessments, providing an improved indication of ecosystems' vulnerabilities to both natural and human perturbations. This research will integrate principles of Political Science, Environmental Sociology, and Social-Ecological Systems theories and apply it to the Edwards Aquifer, a major source of water for south central Texas. Political Science theory will be used to describe the political system that determines or influences the outputs, or laws, of the Edwards Aquifer system; Schnaiberg's ecological continuum theory will be used to evaluate the Edwards Aquifer social system's consideration of natural resource preservation versus development; and Social-Ecological System theory will be used to explore the Edwards Aquifer system's adaptability, connectedness, and vulnerability to human and natural perturbations. Using the Edwards Aquifer as a test case, this research will 1) evaluate current and historical composition of Edwards Aquifer stakeholders and their impact on the development of Edwards Aquifer policies, 2) describe a historical and hierarchical account of these policies, and 3) analyze the dynamics of stakeholder and policy interactions.