Understanding the ecological processes that impact parasite abundance and distribution is critically important for epidemiology and predicting how infectious disease dynamics may respond to future disturbance. Digenean trematodes (Platyhelminthes: Trematoda) are parasitic flatworms with complex, multi-host life cycles that include snail first-intermediate hosts and vertebrate definitive hosts. Trematodes cause numerous diseases of humans (e.g. schistosomiasis) and livestock (e.g. fascioliasis), and impact the ecology of wildlife systems. Identifying the ecological mechanisms that regulate these complex, multi-host interactions will advance both our understanding of parasitism and the dynamics of infectious disease. By examining patterns of infection in Elimia (= Oxytrema = Goniobasis) proxima snails, my dissertation research investigated the environmental factors and ecological processes that structure trematode communities in streams. First, I examined temporal variation in trematode infection of snails in five headwater streams. Over a three year period, I found no consistent seasonal patterns of trematode infection. There was consistency across sites in trematode prevalence, as sites with high prevalence at the beginning of the study tended to remain sites of high infection, relative to lower prevalence sites. Second, I examined landscape level variation in trematode infection by characterizing the regional distribution, abundance and diversity of E. proxima infections in 20 headwater streams. I found a broad scale spatial pattern in trematode communities due to regional turnover in dominant species. This pattern was correlated with elevation, but there were no significant relationships with other environmental variables. Additionally, molecular characterization of trematodes indicated the presence of cryptic (morphologically indistinguishable) species complexes within this system, and variation in genetic diversity among trematode types may reflect differences in host dispersal abilities. Third, I examined trematode infection within a single stream network across multiple headwaters and the mainstem. I found a decreasing downstream gradient of trematode prevalence related to several environmental variables including elevation, snail density, conductivity, and stream depth. Additionally, headwater communities were nested subsets of the communities found in the mainstem. By combining approaches at different temporal and spatial scales, my dissertation research increases our understanding of the processes that impact the abundance and distribution of parasites. / Ph. D.

Anthropogenic salinization of freshwater is a global concern. In freshwater environments, elevated levels of major ions, measured as total dissolved solids (TDS) or specific conductance (SC), can cause adverse effects on aquatic ecosystem structure and function. In central Appalachia, eastern USA, studies largely rely on Rapid Bioassessment Protocols with semi-quantitative sampling to characterize benthic macroinvertebrate community response to increased salinity caused by surface coal mining. These protocols require subsampling procedures and identification of fixed numbers of individuals regardless of organism density, limiting measures of community structure. Quantitative sampling involves enumeration of all individuals collected within a defined area and typically includes larger sample sizes relative to semi-quantitative sampling, allowing expanded characterization of the benthic community. Working in central Appalachia, I evaluated quantitative and semi-quantitative methods for bioassessments in headwater streams salinized by coal mining during two time periods. I compared the two sampling methods for capability to detect SC-induced changes in the macroinvertebrate community. Quantitative sampling consistently produced higher estimates of taxonomic richness than corresponding semi-quantitative samples, and differences between sampling methods were found for community composition, functional feeding group, dominance, tolerance, and habit metrics. Quantitative methods were generally stronger predictors of benthic community-metric responses to SC and were more sensitive for detecting SC-induced changes in the macroinvertebrate community. Quantitative methods are advantageous compared to semi-quantitative sampling methods when characterizing benthic macroinvertebrate community structure because they provide more complete estimates of taxonomic richness and diversity and produce metrics that are stronger predictors of community response to elevated SC. / Master of Science / Surface coal mining in central Appalachia, eastern USA, contributes to increased salinity of surface waters, causing adverse effects on water quality and aquatic life. Stream condition is often evaluated through sampling of benthic macroinvertebrates because they are ubiquitous in aquatic environments and differ in sensitivity to various types of pollution and environmental stressors. In central Appalachia, studies have largely relied on semi-quantitative sampling methods to characterize effects of elevated salinity on benthic macroinvertebrate communities in headwater streams. These methods are ‘semiquantitative’ because processing of samples requires subsampling procedures and identification of a fixed number of individuals, regardless of the number of organisms that were originally collected. In contrast, quantitative sampling involves identification and counting of all collected individuals, often resulting in organism counts that are much higher than those of semi-quantitative samples. Quantitative samples are typically more time-consuming and expensive to process but allow for expanded description of the benthic macroinvertebrate community and characterization of community-wide response to an environmental stressor such as elevated salinity. Working in central Appalachian streams, I compared 1) depictions of benthic macroinvertebrate community structure; 2) benthic community response to elevated salinity; and 3) the minimum levels of salinity associated with community change between quantitative and semi-quantitative methods. Quantitative sampling methods provide many advantages over semi-quantitative methods by providing more complete enumerations of the taxa present, thus enhancing the ability to evaluate aquatic-life condition and to characterize overall benthic macroinvertebrate community response to elevated salinity caused by surface coal mining.

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We study a message passing network where nodes keep a numeric attitude toward a subject. Messages are created by a message factory and each is sent to a random seed-node, which then gets eventually propagated in the network. Each message has some information about the subject, which is interpreted by the receiving node based on its features. Hence, the same message could be interpreted quite differently by two different nodes. Once a message is interpreted, the attitude of the node toward the subject is updated. In this setting, the thesis is that an external agent can influence (in a desired way) the average attitude of the network, by sending the messages to specific nodes (rather than sending them randomly) based on the message content. We call this agent a leader which its goal is to minimize (maximize) the average attitude of the network, and its actions are choosing one of the seed-nodes for a given message. The leader does not have any information about the nodes in advance, instead, it eventually learns the interests of the seed-nodes through sending messages and receiving the feedback of the network. We formulate this as a contextual bandit problem and study the effectiveness of a leader in different network configurations. Moreover, we study the case that there are two adversarial leaders, and present different policies and evaluate their effectiveness. Finally, we study the leader's performance when there are dynamic changes in the nodes features and network's topology.

Flow variability plays an important role in structuring lotic communities, yet comparatively little is known about processes governing assemblage dynamics in stream ecosystems with stable environmental conditions, such as spring-fed rivers. Volcanic spring-fed rivers (hereafter spring-fed rivers) occur in geologically active landscapes of the western USA and around the globe. We sampled invertebrate assemblages and quantified primary productivity and habitat characteristics of spring-fed and runoff rivers in northern California over 4 seasons. We predicted that abiotic factors would be more stable and nutrient availability greater and that invertebrate density would be greater and diversity lower in spring-fed than in runoff rivers. Runoff rivers exhibited high variability in discharge and temperature, whereas spring-fed rivers were relatively stable with high naturally occurring nutrient levels. On average, NO3- and PO43- concentrations were 40x greater in spring-fed than in runoff rivers. Spring-fed rivers supported nearly 7 to 16x greater densities of invertebrates than runoff systems, depending on season. However, invertebrate species richness was greater in runoff rivers in all seasons. Spring-fed river invertebrate assemblages were strongly correlated with elevated nutrient concentrations and basal C sources, whereas runoff assemblages were associated with discharge variability and median substrate size. We suggest that strong differences in abiotic variability between spring-fed and runoff rivers play an important role in determining invertebrate assemblage structure. Because spring-fed rivers exhibit more stable temperatures throughout the year and lower temperatures during the summer than runoff rivers, they may provide essential refugia for coldwater taxa in a warming climate.

Nitrification is a biological oxidation of NH3 to NO2- and then to NO3-. Understanding how the nitrifier community responds to agricultural management is essential because the community composition is complex and functional distinction of subgroups occurs. Better managing nitrifiers could benefit the environment by increasing nitrogen (N) fertilizer use efficiency, decreasing NO3- leaching, and reducing NO and N2O emissions. This study examined how long-term N fertilization and tillage influenced nitrifier density, ratios, nitrification rates, and the community structure of ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA), and nitrite-oxidizing bacteria (NOB). The study site was a long-term (>40 years) continuous maize (Zea mays L.) experiment with three N fertilization rates (0, 168, and 336 kg ha-1) and either no-tillage (NT) or plow tillage (PT). Most Probable Number method was used to estimate the density of AOB and NOB; the shaken slurry method was used to measure potential nitrification rates; PCR-denaturing gradient gel electrophoresis (DGGE) was used to analyze nitrifier communities. Tillage, fertilization, and their interaction all significantly influenced the AOB and NOB densities, the ratio of AOB to NOB, and potential nitrification rate. Nitrifier densities and potential nitrification rates increased with increased N fertilization; NOB density increased faster than AOB density with fertilization. The influence of tillage on nitrification was different for different fertilization rates. The trends for nitrifier density and potential nitrification rate were not consistent. Nitrifier community structure was influenced by sample season, N fertilization rates, tillage, and their interaction. Different nitrifier groups had different responses to the treatments. The AOB became more diverse with increasing N input; tillage rather than N fertilizer played a dominant role affecting the AOA community; two NOB genera had different responses to N fertilization rates: Nitrobacter diversity increased with more N applied; Nitrospira was the opposite. Unique bands/members were discovered in different treatments, manifesting environmental selection. Long-term field trials were useful in better understanding how soil management influenced the relationship between nitrifier densities, nitrification rates, and community structure, which may facilitate new approaches to optimize nitrification and provide new clues to discover which environmental factors most influence the nitrifier community in agroecosystems.

This study is an investigation of the relationship between selected structural characteristics of the community and innovation among cities. Four major Structural characteristics were chosen to serve as independent variables. These independent variables were community differentiation, community poverty, community maturity and type of local government. Innovation, as measured by applicant status to the federal Urban Development Action Grant Program, served as the dependent variable. Analysis of the data indicated support for several of the postulated hypotheses. The structural characteristic community differentiation was found to be significantly related to applicant status. For the structural characteristic community poverty no significant relationship to applicant status was observed. Community maturity revealed a significant relationship to applicant status. Finally, for the structural characteristic local form of government a significant relationship with applicant status was observed. Based on the interpretation of the findings, an original typology of innovation was developed. This typology included planned revitalizing innovation, social enhancing innovation, entrepreneurial stimulating innovation, and needs inducing innovation.

This paper investigates whether a new conceptual framework, Neighborhood Ritual Integrity (NRI), addresses the concepts of social capital, collective efficacy, and rituals in a manner which makes it applicable to sociological research. Neighborhood Ritual Integrity (NRI) is a conceptual framework developed in response to various studies, which have established a relationship between neighborhood demographics, structural neighborhood features, crime and adolescent behaviors. Kiser et al., (2007) identified six dimensions that influence short and long term community functioning: Ritual Integrity, Daily Routines, Role Clarity, People and Organizational Resources, Deliberate Planning, and Meaning Making as aspects of NRI. Each dimension describes either a structural or cultural component of community level processes that could affect positive features of neighborhood life. Results from focus group data are examined for the existence of responses consistent with the conceptual definitions of NRI as well as social capital, collective efficacy, and rituals in hopes that this investigation will develop a more comprehensive sociological approach to the study of neighborhoods.

In wetland soils, hydrology is considered to be one of the primary factors shaping wetland function and microbial community structure, but plant-soil interactions are also important mechanisms affecting microbial nutrient transformations. The research presented here considered the interactive effect to describe how hydrology and the presence of plants alter the soil profile, the development of the bacterial community, and their associated functions. To achieve this goal, plots were established in three hydrologically-distinct regimes (Wet, Intermediate, and Dry) within a non-tidal freshwater wetland along the James River (Charles City County, Virginia). Inside each main plot, ten subplots were cleared of all aboveground plant material; five plots were left to re-grow (“Vegetated” reference), while the remaining five were weeded each week to maintain bare soil (“Clipped” treatment subplots). Manipulations were started at the beginning of the growing season, and sampling continued until the following winter. Every eight weeks, soil cores (30 cm) were collected and analyzed for a variety of soil properties (e.g., pH, OM, C:N, redox, vegetation and root biomass), microbial community structure (16S-rDNA-based T-RFLP),bacterial abundance (Acridine Orange Direct Count), and soil function (Extracellular Enzyme Activity (EEA)). A mixed-effects repeated measures analysis of variance (ANOVA) was used to better understand how each variable responded within each hydrological regime and treatment. Principal component analysis (PCA) and Partial Mantel tests were used to elucidate how saturation and vegetation influence the microbial community structure and soil enzyme function. Bacterial community properties and soil functions followed differences in soil saturation and associated physicochemical parameters (i.e., pH and redox). Correlations with wetland vegetation were primarily related to seasonal changes in plant community composition and biomass, and differences between experimental treatments were small. Evidence suggests the present plant species and the amount of above- and belowground biomass plays a more selective role shaping bacterial communities and soil function. Due to the short-term of this study and tight soil correlations, it is difficult to determine if observed differences are a product of the plant community or soil saturation, but it is clear that each is important. Based on the literature, plant effects were smaller in this wetland than might be expected. This experiment took place in a recently exposed lake basin, so plant-soil-microbe interaction may not be well established. As the wetland matures, relative importance of vegetation is expected to increase and impact bacterial composition and function. Collectively, these results demonstrate that wetlands are not a product of one separate variable, but result from various factors interlinked to shape microbial communities and soil functions.