Browsing by Subject "ecology"
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Item Assessing the Oceanographic Conditions and Distribution of Reef Fish Assemblages Throughout the Gal?pagos Islands Using Underwater Visual Survey Methods(2014-12-12) Durkacz, StephanieThe Gal?pagos Islands are one of the most diverse marine ecosystems in the world because they lie at the confluence of several ocean currents in the eastern tropical Pacific Ocean (ETP). The Gal?pagos Marine Reserve (GMR) is a 138,000 km^2 area surrounding the archipelago that is divided into several zones based on the dispersal of fauna and marine resources. The goal of this thesis was to assess the distribution and abundance of reef fish assemblages throughout the GMR and to contribute to the existing knowledge of these assemblages. This project was performed during three visits to Gal?pagos: 16-30 May 2013, 16-19 November 2013, and 12-24 July 2014. Reef fish assemblage composition throughout the GMR was examined by collecting qualitative and semi-quantitative data using underwater visual survey techniques. Data on current and past oceanographic conditions around Gal?pagos were collected through in situ measurements and examining data collected by satellites. Underwater surveys found a high species richness and wide range of trophic levels to exist across the Gal?pagos archipelago. Data were analyzed using several techniques including rank order of abundance (ROA), hierarchical cluster analysis, principal coordinates analysis, and regression. During 2013 surveys, 60 species from 32 families were recorded at 12 survey sites across the GMR. Through tests of similarity, it was found that fish assemblages across the GMR are not uniformly distributed and vary spatially. Ocean conditions such as temperature may influence fish assemblage composition at different islands. These results support previous studies that surveyed fish assemblages throughout the GMR and found that assemblages vary based on geographic location and that water temperature may play a role in how they are structured. In July 2014, data were collected around the northwest coast of Isla San Crist?bal at two sites previously surveyed in 2013. Fish assemblages around San Crist?bal showed little change from one year to the next in terms of species richness and diversity. Ocean temperatures were warmer and chlorophyll-a levels were lower in 2014 than in 2013, caused in part by El Ni?o climactic variations in the ETP during 2014. Information from this thesis may be used for a variety of applications including marine resource management and to support future zoning proposals in the GMR.Item Ecological Consequences of Landscape Fragmentation on the Lizard Community in the Mescalero-Monahans Shinnery Sands(2012-10-29) Leavitt, Daniel 1979-Landscape fragmentation poses a major threat to biodiversity world-wide. The goal of my dissertation research was to determine the effects of landscape fragmentation on a lizard community in the Mescalero-Monahans shinnery sands, New Mexico and the extent to which conservation efforts might protect biodiversity in this ecosystem. My research relied heavily on data collected from a large-scale spatially-replicated comparative study. The purpose of this study was to evaluate the impacts of landscape fragmentation as a result of oil and gas development on the dunes sagebrush lizard (Sceloporus arenicolus). Results from analysis of lizard community structure indicate that fragmented sites are less diverse than non-fragmented sites. In particular, two species are found in lower density and occupancy in the fragmented locations (Holbrookia maculata and Sceloporus arenicolus). Analysis of landscape configuration at the scale of a trapping grid indicated that sand dune blowout shape and size differed between fragmented and non-fragmented locations. Differences in landscape pattern were associated with reduced lizard diversity. Because of this association between lower diversity and altered landscape pattern, extensive alterations to landscape pattern may cause disassembly at the ecosystem level. The maintenance of existing landscape pattern may be important to the maintenance of diversity in this ecosystem. Evaluations of habitat use patterns of the lizards in this community demonstrate that a few species have narrow preferences for certain habitats. In particular, H. maculata, Phrynosoma cornutum, and S. arenicolus all demonstrated narrow habitat use patterns. Effect size of fragmentation for each species indicated that the same three species showed a large effect when comparing their average abundances between fragmented and non-fragmented locations. Thus species that are most likely to benefit or be harmed by landscape fragmentation are those with the most specific habitat requirements. Umbrella species represent one of many approaches to conservation using surrogate species. I used data on ants, beetles, small mammals, lizards, and endemic species to test the use of the dunes sagebrush lizard (Sceloporus arenicolus) as an umbrella for endemism and biodiversity of the Mescalero-Monahans shinnery sands ecosystem. I applied a comparative approach at three spatial scales to examine how conservation practices at different scales may affect biodiversity and endemism in this ecosystem. At the largest scale, the frequency of occurrence for endemic species increased though no other patterns emerged because S. arenicolus was present at all sites and there were no relationships between relative abundances of S. arenicolus and the other taxonomic groups. At the smallest scale, both beetle species richness, diversity, and endemic species richness were higher in the presence of S. arenicolus. To protect biodiversity in this ecosystem, conservation efforts should focus on protection at the scale of the species distribution rather than on the small-scale placement of individual well pads.Item Ecology and transmission dynamics of Everglades virus(2005-10-20) Lark Lee Arwen Coffey; Douglas Watts; Daniel Brooks; Billy PhilipsEverglades virus (EVEV), an alphavirus in the Venezuelan equine encephalitis (VEE) serocomplex, circulates among rodents and vector mosquitoes in Florida and occasionally infects humans, causing a febrile disease sometimes accompanied by neurological manifestations. \r\nEVEV infections of cotton rats from Florida, and from Texas, a non-endemic area were performed to validate their role in enzootic transmission and to evaluate whether the viremia induced regulates EVEV distribution. Cotton rats from both localities developed viremia levels that exceeded the threshold for infection of the vector indicating that rat susceptibility does not limit EVEV distribution. \r\nSusceptibility experiments were performed with _Aedes taeniorhynchus_ and _Culex nigripalpus_, potential EVEV vectors, to evaluate their permissiveness to EVEV infection. In contrast to the high degree of susceptibility of the established vector _Culex (Melanoconion) cedecei_, these two species were relatively refractory to oral EVEV infection, indicating that they are probably not important vectors. \r\nPet dogs were used as sentinels of EVEV activity to detect recent circulation and to delineate EVEV distribution. Four percent of Florida dog sera contained EVEV antibody and many animals lived farther north than recorded EVEV activity, indicating that EVEV is widespread in the state and may be a cause of undiagnosed febrile illness in residents.\r\nDespite evidence that enzootic subtype ID Venezuelan equine encephalitis viruses (VEEVs), the closest relatives of EVEV, have emerged to cause significant human and equine disease, EVEV has not caused outbreaks in Florida. Venezuelan equine encephalitis virus emergence can be mediated by adaptation to epizootic mosquito vectors via mutations in the E2 glycoprotein gene. EVEV may accrue similar E2 mutations resulting in epizootic disease in Florida. The role of the EVEV E2 gene in epizootic vector infection was evaluated with a VEEV/EVEV E2 chimera. Insertion of the EVEV E2 into the VEEV backbone reduced infection in _Ae. taeniorhynchus_ by 40%, indicating that the epizootic VEEV E2 is necessary for infection of epizootic vectors. \r\nThe intrinsic plasticity of RNA viruses can facilitate changes in host range that may cause epidemics. However, the evolutionary processes that promote cross-species virus transfers are poorly defined, especially for generalist RNA arboviruses that replicate alternately in arthropods and vertebrates and often exhibit slower evolutionary rates than other RNA viruses with similar mutation frequencies that replicate only in vertebrates. The observed genetic stability of RNA arboviruses may result from constraints imposed by alternating between disparate hosts, where optimal replication in one host involves a fitness tradeoff for the alternate host. Accordingly, freeing RNA arboviruses from the alternate replication cycle, and thereby allowing them to specialize in a single host, will facilitate faster evolution and adaptation. To test this hypothesis in vivo, VEEV was passaged serially in mosquitoes or in vertebrates to eliminate host alteration, or alternately between mosquitoes and vertebrates. Virus lineages allowed to specialize in mosquitoes exhibited increased mosquito infectivity, and vertebrate-specialized strains produced higher viremias. Alternately passaged VEEV exhibited no detectable fitness gains in either host and serial passaged VEEV exhibited fitness declines in the bypassed host. These results support the hypothesis that arbovirus adaptation and evolution is limited by obligate host alternation. \r\n\r\nItem Ecology of Owens Valley vole(Texas A&M University, 2005-08-29) Nelson, Fletcher ChrisLittle current data exist concerning the status and ecology of Owens Valley vole (OVV; Microtus californicus vallicola), despite its California Department of Fish and Game listing as a Species of Special Concern. No formal studies have been undertaken to understand the ecology of OVV or other small mammal species occurring in mesic-vegetative communities in Owens Valley, California. I investigated the relative abundance of small mammal species in mesic-plant associations of Owens Valley, OVV distribution, and OVV use of vegetative types as habitat. Low OVV capture rates decreased the efficiency of systematic trapping surveys. Live trapping and sign surveys yielded contradictory results. The distribution of OVV was associated with irrigation and microhabitat features such as waterways, fence lines, and brush patches. The distribution and use of vegetation types by OVV was similar to that of the California vole (M. californicus).Item Effects of juniper removal by shearing and dozing on seedbed preparation and vegetation establishment in the Lampasas Cut Plain, Texas(2009-05-15) Mannel, Cheryl K.Woody encroachment upon grasslands is a global trend that is cause for concern. In the Lampasas Cut Plain of Texas, Ashe juniper is the dominant woody invasive species. Grassland restoration is dependent upon proper seedbed preparation and seedling establishment. Shearing and bulldozing are common methods of juniper removal. Three hypotheses were tested in this experiment. The first was that bulldozing and shearing results in similar seedbed preparations. The second was that electrical conductivity (ECa) models soil moisture storage heterogeneity across a landscape. The third hypothesis tested was that bulldozing and shearing result in similar seedling establishment. Eighteen plots were selected and three treatments were applied: 1) shearing, 2) dozing, and 3) control. After clearing with both juniper removal methods, the levels of soil disturbance and vegetation regrowth were measured. Point measures were used to describe soil surface disturbance, and at each point, presence and size of ground cover and surface depressions were recorded. After germination, when the plants were large enough to identify, vegetation was sampled at 20-24 locations in each plot. At each sample location a quadrat was placed on the transect, and total herbaceous, grass, forb, rock, litter, and bare soil cover were recorded in cover classes. All species were identified, seeded species were enumerated, and in the second vegetation sample, dominant species were assigned a cover class. There was considerable variation between plots for all parameters measured. Bulldozing created a greater number of depressions in the soil than shearing. It also had a higher percent of large depressions. There was no difference in ground cover change between treatments except in the case of the largest litter category. ECa was effective in modeling soil moisture storage patterns and had a lower coefficient of variation than manual soil depth measurements. There was no difference between sheared and dozed plots for any of the vegetation establishment parameters, but control plots had lower establishment in most categories. Overall, there was little difference between the two treatments in seedbed preparation and seedling establishment. The cost of shearing was 80% of the cost of dozing, which made it more desirable in this scenario.Item Evaluation of the Gastrointestinal Microbiota in Response to Dietary and Therapeutic Factors in Cats and Dogs Using Molecular Methods(2012-02-14) Garcia-Mazcorro, JoseThe gastrointestinal (GI) tract of cats and dogs is inhabited by many different types of microorganisms, known as the GI microbiota. Mounting evidence suggests that the administration of certain dietary and/or therapeutic agents can alter the composition and activity of the GI microbiota, thus influencing gastrointestinal health and disease. The aim of this study was to evaluate the gastrointestinal microbiota in response to dietary and therapeutic interventions in cats and dogs. A multi-species synbiotic formulation, containing a total of 5x109 colony forming units of a mixture of seven probiotic bacterial strains and a blend of prebiotics, was administered daily for 21 days to healthy cats and dogs. Fecal samples were collected before, during, and up to three weeks after discontinuation of the administration of the synbiotic. The fecal microbiota was analyzed using 454-pyrosequencing, denaturing gradient gel electrophoresis, quantitative real-time PCR, and 16S rRNA gene clone libraries. The results showed that the synbiotic led to increased concentrations of probiotic bacteria in the feces but did not alter the predominant bacterial phyla. Additionally, we investigated the effect of age, body weight, and baseline abundance of probiotic related bacterial genera, as potential predictors of intestinal colonization by the ingested microorganisms. The results suggested that cats having a low abundance of fecal probiotic genera before consuming probiotics may have a higher concentration of the probiotic groups in feces during consumption of the symbiotic formulation. Also, a proton-pump inhibitor, aimed at suppressing the secretion of gastric acid, was administered daily for 15 days to healthy dogs. Changes in the GI microbiota were analyzed using 454-pyrosequencing, fluorescent in situ hybridization, and quantitative real-time PCR. The results suggested that inhibition of gastric acid secretion can alter the abundance of several gastric, duodenal, and fecal bacterial groups. However, these changes were not associated with major qualitative modifications of the overall composition of the GI microbiota. These studies showed that dietary and therapeutic agents can alter the composition of the GI microbiota and suggest that these changes could be associated with particular characteristics of the host. The clinical significance of these results needs further investigation.Item Experimental studies of the ecology and evolution of eastern equine encephalitis virus and implications for its emergence and classification(2010-06-25) Nicole Cherise Arrigo; Scott C. Weaver; Michael J. Turell; Ilya V. Frolov; Frederick A. Murphy; Douglas M. WattsEastern equine encephalitis virus strains from North (NA EEEV) and Central/South America (SA EEEV) have developed markedly different epidemiologic, pathogenic, antigenic, and genetic profiles, have distinct geographic distributions, and potentially occupy unique vector and vertebrate ecological niches. The goal of my research was to clarify the extent to which these viruses have diverged by further understanding their evolutionary history and adaptation to different ecological niches, and the impact that this divergence has had on their ability to emerge in reciprocal environments. My studies were designed to examine each of the three main aspects of the arboviral transmission cycle: the virus, the vertebrate host, and the mosquito vector. To investigate the evolutionary history and genetic divergence of NA and SA EEEV, I conducted a phylogenetic and Bayesian coalescent analysis of the structural polyprotein genomic region (26S) of all available SA EEEV, and additional NA EEEV, isolates spanning a broad geographic and temporal spectrum. In accordance with support provided by the evolutionary and phylogenetic analyses, I sought to apply a more direct and experimental approach to explore the adaptation of NA and SA EEEV to the use of different vertebrate host species. Wild cotton rats (Sigmodon hispidus) and house sparrows (Passer domesticus) were collected in Galveston and Houston, Texas, respectively, and evaluated for their potential to serve as amplification and/or reservoir hosts for NA and SA EEEV. Juvenile cotton rats experienced complete mortality with both NA and SA EEEV and provided me with a unique opportunity to compare the pathology resulting from NA and SA EEEV infection a wild vertebrate species. In order to better understand the directionality of NA EEEV divergence and adaptation and to further clarify the vector ecology of SA EEEV, I evaluated the relative susceptibilities of the NA enzootic vector, Culiseta melanura, and the presumed enzootic vector for SA EEEV, Culex taeniopus, and the probable epizootic EEEV mosquito vectors, Aedes (Ochlerotatus) taeniorhynchus and Ae. (Och.) sollicians, to sympatric and allopatric EEEV strains. Taken together, the results of my dissertation research emphasize the striking extent of evolutionary divergence between NA and SA EEEV and provide a greater understanding of the directionality of NA EEEV adaptation to North America subsequent to its divergence from an ancestral EEEV in Central/South America. My research has also clarified the vector and vertebrate usage of both NA and SA EEEV, providing support for the use of mammalian vertebrate host species by SA EEEV and highlighting its emergence potential in a novel North American environment.Item Exploring the Possible Relationships between Terrestrial Arthropod and Plant Community Structures in the South Texas PlainsCampbell, Chad; Mott, DanielThe South Texas Plains is one of many locations worldwide that has rapidly changed from grass-dominated rangeland into a relatively densely wooded thicket; a mechanism of succession termed the “mesquite-nucleus hypothesis,” which states that a mesquite tree is well evolved to encroach on grassland and change the micro-habitat, thereby allowing other woody species to encroach more easily, has been proposed. The current study tests the mesquite-nucleus hypothesis by studying arthropod community structure and its relationship to the surrounding plant community structure. Arthropods are easily trapped and counted, but complete survey data for South Texas is sparse. Pitfall traps were used in three distinct transect lines to collect arthropods between 19 September 2015 and 31 March 2016. Most arthropods were identified to the order level, spiders were identified at the family level, and ants were keyed to the genus level. Relative abundances, direct comparisons of relative abundances, Simpson indices, Shannon indices, G-tests of independence, richness extrapolation, and richness estimation were used to compare arthropod community structure among the transect lines, and the point-centered quarter method was used to characterize plant communities and place traps. The mesquite-nucleus hypothesis is weakly supported by some of the data, but experimental replicants are needed. Overall, evenness and diversity were highest in the mesquite transect, but the transect dominated by blackbrush had the highest arthropod abundance. The relative abundance data for several taxa raise questions that should be further investigated: Diptera abundances seem negatively correlated with the average distances between shrubs or perhaps prefer to be near blackbrush, Salticids were found to prefer blackbrush, and Gnaphosids were disproportionally present in the transect referred to as mixed. Ant communities were similar among transects.Item Social organization of the New Zealand dusky dolphin(Texas A&M University, 2004-09-30) Markowitz, Timothy MichaelSocial organization of dolphins in extensive societies has not been well studied. Off Kaikoura, New Zealand, thousands of dusky dolphins (Lagenorhynchus obscurus) gather, feeding nocturnally on deep scattering layer prey, resting and socializing diurnally. During 1997-2003, interval sampling was used to monitor large assemblages numbering hundreds (n=169), smaller mating groups (mean+s.e.=7+1.6 adults, n=42), mother-calf nurseries (mean+s.e.=13+1.6 adults, 1+0.5 juveniles, 4+0.7 calves and 1+0.4 neonates, n=41), and non-mating adult groups (mean+s.e.= 9+1.3 adults, 1+0.2 juvenile, n=37). Group size, distance from shore (east), ranging along shore (north), traveling, inter-individual distance, and noisy leaping peaked in winter (n=39), with dolphins maintaining closer proximity to each other in smaller, more restful groups, closer to shore during the spring-summer-autumn (n=234) reproductive seasons. Dolphin groups were found closest to shore (west) during early morning, spread out and leaping often. Resting peaked at midday in tight groups. Late in the day, dolphins spread out, moving eastward (offshore) in preparation for feeding. Large groups exhibited coordinated travel, with noisy leaps as a directional signal. "Mating of the quickest" occurred in groups of (median) 6 males chasing 1 female. Leaping rarely occurred in restful nurseries, which at times associated with Hector's dolphins (Cephalorhynchus hectori). Other mixed-species groups included common dolphins (Delphinus delphis), southern right whale dolphins (Lissodelphis peronii), long-finned pilot whales (Globicephala malaena), and bottlenose dolphins (Tursiops truncatus). Killer whales (Orcinus orca) elicited predator assessment and evasion. Whale riding occurred with larger whales. Residence was seasonal, with 1,969+814.9 from a population of 12,626 dolphins spending 103+38.0 days in Kaikoura (mean+s.e., mark-recapture mortality, single-season lagged-ID emigration models, n=153 weeks). Dolphins (n=39) summering in Kaikoura migrated to the Marlborough Sounds in winter, where small, coordinated groups foraged diurnally on schooling fishes in shallow bays, often associated with sea birds and New Zealand fur seals (Arctocephalus forsteri). Aquaculture may threaten dusky dolphin foraging habitat in Admiralty Bay, where an estimated 220 dolphins gathered to feed each winter. Photo-identification research, enhanced by digital techniques, demonstrated a structured fission-fusion society. Dusky dolphins associated with preferred long-term (>1,000 days) hunting companions in Admiralty Bay and non-random casual acquaintances (200 days) in Kaikoura (lagged-association models).Item The role of piscivores in a species-rich tropical river(Texas A&M University, 2004-11-15) Layman, Craig AnthonyMuch of the world's species diversity is located in tropical and sub-tropical ecosystems, and a better understanding of the ecology of these systems is necessary to stem biodiversity loss and assess community- and ecosystem-level responses to anthropogenic impacts. In this dissertation, I endeavored to broaden our understanding of complex ecosystems through research conducted on the Cinaruco River, a floodplain river in Venezuela, with specific emphasis on how a human-induced perturbation, commercial netting activity, may affect food web structure and function. I employed two approaches in this work: (1) comparative analyses based on descriptive food web characteristics, and (2) experimental manipulations within important food web modules. Methodologies included monthly sampling of fish assemblages using a variety of techniques, large-scale field experiments, extensive stomach content and stable isotope analyses. Two themes unite the information presented: (1) substantial spatial and temporal variability in food web structure, and (2) how body-size can be used to generalize species-interactions across this complexity. Spatial variability occurred at various scales, from among small fish assemblages on seemingly homogeneous sand banks, to differences among landscape scale units (e.g. between lagoons and main river channel). Seasonal variability was apparent in predation patterns, with relative prey availability and body size primarily resulting in decreasing prey sizes with falling water levels. Body size was also related to functional outcomes of species interactions, for example, a size-based response of prey fishes to large-bodied piscivore exclusion. This pattern was further substantiated at the landscape-scale, as differences in assemblage structure among netted and un-netted lagoons were largely size-based. Trophic position of fish and body size was not found to be related, likely due to the diversity of prey available to consumers, and may signify that commercial netting activity will not decrease food chain lengths. In sum, by describing human impacts within a food web context, I endeavor to provide predictive power regarding a specific human-induced environmental problem, yet still allowing for generality that will broaden the theoretical foundations and applications of food web ecology.