Theses and Dissertations from UMD
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Item Spatio-temporal mechanisms of urban mosquito coexistence in Baltimore, MD(2019) Saunders, Megan Elizabeth Maria; Leisnham, Paul T.; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Understanding the interactions governing species distributions and community structure are of fundamental ecological importance. Mosquitoes that utilize container habitats at their larval stage usually engage in strong competition and competitive exclusion is expected; however, numerous container-utilizing mosquito species co-occur in the same individual container habitats and regionally coexist. I investigated spatial and temporal mechanisms governing the distributions and abundances of the competitively superior invasive Aedes albopictus and resident Culex spp. mosquitoes in four neighborhoods with varying socioeconomic status in Baltimore, Maryland. Specifically, I investigated if the findings from both field surveys and field and laboratory experiments were consistent with four spatial and temporal hypotheses for species coexistence that act at different scales: spatial partitioning among neighborhoods and blocks, seasonal condition-specific competition, aggregation among individual container habitats, and priority colonization effects within individual containers. I found modest but important evidence for all hypotheses that could each facilitate Culex spp. coexistence with Ae. albopictus. I found clear neighborhood effects, with low SES neighborhoods supporting higher abundances of mosquitoes than high SES neighborhoods overall, but with the highest abundances of Ae. albopictus in low SES neighborhoods and Culex spp. being more variable among neighborhoods. Culex spp. abundances were higher in the early summer compared to mid-summer peaks in abundance for Ae. albopictus. Laboratory competition trials showed increased aggregation of Ae. albopictus had a slight positive effect on Culex spp. population performance, and aggregation conditions sufficient for coexistence among experimentally placed ovitraps and negative associations of Aedes and Culex genera in resident containers in the field. Lastly, I found that priority colonization of a container leads to stronger population performance for both species, and that resource availability seems to affect Culex spp. more than competition. The results of my dissertation have revealed the role of several ecological mechanisms that may facilitate the regional coexistence of Culex spp. with Ae. albopictus and is among the first bodies of work to do so. Due to their roles in the transmission of human pathogens, future examination of other spatial and temporal mechanisms of coexistence between Ae. albopictus and resident Culex spp. is warranted.Item REPUTATION DYNAMICS IN MARKETING CONTEXTS(2019) Ukanwa Zeiger, Kalinda Ukanwa; Godes, David; Rust, Roland T.; Business and Management: Marketing; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation is an examination of the impact of dynamic consumer reputation effects on firm decision-making in the marketplace. Essay I is a study of the impact of firm interventions on competitive reputation building among consumers on an online platform. Specifically, I model an actor’s decision to upload pirated content in order to build his reputation, despite facing threats from copyright lawsuits (firm interventions seeking to deter uploading activity) and intense competition on the platform. We propose a novel theory that explains what could occur in this scenario: high-reputation consumers will decrease their reputation-building activity, but their low-reputation competition may see an opportunity to enhance their reputation and increase activity. We argue that because competition for reputation is active on the site, the lawsuits may deter uploading in the short-run but may actually lead to more piracy over the long-run. Our findings support the theory: while high-reputation publishers decrease the likelihood of uploading as lawsuits increase, low-reputation uploaders do the opposite: they upload more. Essay II is an examination of the impact that a consumer group's reputation can have on firm decision-making. Specifically, we investigate 1) conditions under which a non-prejudiced firm may discriminate in service against its consumers based on group reputation, and 2) how subsequent consumer word-of-mouth can impact demand and profits over time. This mixed-methods study shows that discrimination can be profitable in the short-run but can backfire in the long-run due to the effects of consumer word-of-mouth and firm competition. Results indicate that high consumer heterogeneity in quality (i.e., their profitability to the firm) and low measurement error in detecting consumer quality attenuate the magnitude of service discrimination. The authors provide managerial recommendations on reducing service discrimination's profit-damaging effects. This research emphasizes the long-term benefits of switching to a service policy that does not use group reputation information. This dissertation contributes to the general marketing literature by providing new insights into how the reputation of the consumer, a sparsely researched area, can have direct impact on the firm in its decision-making.Item Matchmaking or Information Leakage? Disclosure Benefits and Constraints of Corporate Job Advertisement Specificity(2018) Cao, Yi; Cheng, Shijun; Business and Management: Accounting & Information Assurance; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study examines the benefits and constraints of a special form of corporate voluntary disclosure—job advertisements. Using a novel dataset of over 8 million recruiting advertisements posted by public companies, I follow taxonomy theories and create a continuous measure of information specificity, based upon the level of descriptive detail of skill requirements in job advertisements. Consistent with the theory that labor market disclosure mitigates search frictions, I find job advertisement specificity positively predicts employee satisfaction, productivity, and corporate accounting performance and negatively predicts employee turnover rate. My results further suggest that job advertisement specificity provides incremental information about human capital intangibles and improves the value-relevance of accounting numbers. I also show that the information specificity is constrained by product market competition. Together, my results suggest job advertisement is an important voluntary disclosure channel and that the content of job advertisements is informative to capital- and product-market participants.Item COMPETITIVE RESPONSE OF INVASIVE PLANT SPECIES TO NEIGHBOR PRESENCE, IDENTITY, AND PHENOLOGY ACROSS TWO GROWING SEASONS(2013) Barry, Kevin; Dudash, Michele; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Exotic plant species invade many native communities, yet some communities are less susceptible than others. Community properties that determine resistance to or influence on invasive species performance are less studied. The target-neighbor experimental design, originally used for studies of root and shoot competition (Chapter 1), is now commonly used to determine effects of communities of species on a target plant of interest. However, intensity of competition varies between species both within and across seasons, therefore interactions between species are not static. Thus I compared the competitive response of two widespread but relatively little studied invasive species, early flowering Hesperis matronalis and later flowering Nepeta cataria. Both invasives were introduced into native species neighbor communities composed of either early, late, or a mixture of early and late growth and flowering phenologies and measured over the course of two years (Chapter 2). Additionally, invasive species introduction time into native communities was manipulated by either coestablishing the invasive with the neighbors, or introducing the invasive into established neighbor communities (Chapter 3). I predicted that target invasives would experience the most intense competition (1) when sharing the same growth and flowering phenology as their surrounding native community, due to temporal niche overlap (2) when introduced into an established native community versus when coestablished with native neighbors, and also that (3) the overall effect of neighbor presence and neighbor identity would vary with the age of the competitors. Finally, I utilized field soil probes and greenhouse plants labeled with 15N isotopes to determine the relationship between phenology and nitrogen uptake to provide a mechanistic basis for temporal niche overlap (Chapter 4). The competitive response of both invasive species' performance was dependent on plant trait measured, community age, and native neighbor phenology treatment. I found evidence for a negative effect of temporal niche overlap, but resource pre-emption by the early phenology neighbors was more prevalent than stronger competition due to a shared phenology. Despite this, field nitrogen levels were still correlated with species phenology. This body of work supports the need for more research on the factors associated with native communities' ability to resist invasion.Item Impacts of Climate Change Variables on Mosquito Competition and Population Performance(2011) Smith, Cassandra Dionne; Leisnham, Paul; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Rising CO2 concentrations and the resulting shifts in hydrology can have direct and indirect impacts on organisms and communities. The system studied was aquatic container habitats, where mosquito larvae often compete for food resources. I hypothesized that elevated atmospheric CO2 concentrations (Chapter 2) and extreme precipitation regimes (Chapter 3) would alter leaf chemistry and competition between two locally competing mosquito species, Aedes albopictus and Aedes triseriatus in laboratory microcosm experiments. In Chapter 2, tannin concentration was higher in leaves grown under elevated CO2 conditions than ambient, but competition was not affected. A two-fold increase was observed in leaf biomass in the elevated CO2 chamber, and increasing leaf litter to a container system could increase toxicity to mosquito larvae. In Chapter 3, simulated drought conditions decreased leaf decay rate and increased tannin concentrations compared to continuously wet and wet-dry leaves, and amplified the competitive effects of Ae. albopictus on Ae. triseriatus.Item The neural correlates of psychological momentum(2011) Hunt, Carly; Haufler, Amy; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Psychological momentum has been described as an emergent pattern of competitive success. However, the psychomotor processes underlying psychological momentum have not been characterized. Method: In accord, EEG data were recorded during a head-to-head shooting competition to examine the psychomotor processes underlying psychological momentum. Given that expert level performance has been characterized by psychomotor efficiency (see Hatfield & Hillman, 2001), high levels of momentum were hypothesized to be characterized by psychomotor efficiency, as indicated by reduced task-irrelevant cortical processing (i.e., greater high alpha power and lower gamma power in T3) and reduced non-essential neural networking (i.e., lower T3-Fz low-beta coherence) relative to low levels of momentum. Results: In accordance with psychological momentum theory, the high momentum group exhibited greater self-confidence relative to the low momentum group. Contrary to the hypothesis, the high momentum group exhibited reduced high alpha power relative to the low momentum group. Discussion: As the participants were not expert performers, psychological momentum appeared to facilitate cortical dynamics indicative of superior performance given the stage of motor learning.Item COMPETITION BETWEEN HYDRILLA VERTICILLATA AND VALLISNERIA AMERICANA IN AN OBSERVATIONAL FIELD STUDY AND GREENHOUSE EXPERIMENT.(2010) McChesney, Lauren Dalton; Engelhardt, Katharina; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Invasive species continue to have a pervasive influence on biodiversity but it is often unclear how invasive species affect native species. In field observations and greenhouse experiments, I examined the effect of the non-native submersed aquatic plant Hydrilla verticillata on the native species Vallisneria americana. Field monitoring from 2002 to 2006 showed that coverage of species peaked in 2004 after initial invasion of the estuarine study system in 2002. Substrate characteristics did not limit species distribution. In contrast, substrate and planting density affected plant growth and the outcome of intra- and inter-specific competition in the greenhouse. Although other environmental variables, such as water depth and turbidity, appear to override the effect of substrate in the field, the greenhouse experiment suggests that substrate can be an important driver of submersed aquatic plant community dynamics. Sediment characteristics should therefore be a factor in restoration design and the management of invasive species.Item Evaluating Competition between the Non-native Slug Arion subfuscus and the Native Slug Philomycus carolinianus(2010) Paustian, Megan Elisabeth; Barbosa, Pedro; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The degree to which invasive species have altered the demography, ranges, and microhabitat occupation of native species is poorly known. Yet, the competition-mediated decline of native populations, in concert with other factors such as habitat degradation, can place native species at risk of extirpation. Understanding whether competition between native and non-native species can take place under ordinary environmental conditions can allow us to extrapolate whether native species are likely to have experienced harm in the past and/or if they are likely to do so in the future. The native slug Philomycus carolinianus is likely to compete for resources with the aggressive non-native slug Arion subfuscus in central Maryland forests. In order to establish whether competition occurs between these two species, I tested for the following criteria: the existence of competitive displacement in the field, overlap in the use of limited resources (shelter and food), a decline in the fitness of P. carolinianus in the presence of A. subfuscus, and the action of competition mechanisms (interference and exploitation) between them. Field surveys showed that displacement between A. subfuscus and P. carolinianus does not apparently occur within mixed natural populations. Resource use of the two slugs overlapped, with part of the diet (i.e. fungus) and a large proportion of the microhabitats occupied (i.e. coarse woody debris) in common. A lab experiment established that low natural levels of food (fungus) can limit the fitness of each slug species, while shelter (coarse woody debris) was not limiting. When sharing a low-resource lab cage with either A. subfuscus or conspecifics, P. carolinianus experienced a similar decline in fitness, suggesting that exploitative resource competition was no greater between heterospecifics than between conspecifics. No evidence of heterospecific interference (competition independent of resource levels) was found. Given the limited support for the criteria of competition, A. subfuscus was not shown to be an immediate threat to the persistence of P. carolinianus.Item Kinetics of Tetrachloroethene-Respiring Dehalobacter and Dehalococcoides Strains and Their Effects on Competition for Growth Substrates(2010) Lai, Yenjung; Becker, Jennifer G; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The chlorinated solvents tetrachloroethene (PCE) and trichloroethene (TCE) are common groundwater contaminants. Reductive dechlorination of PCE and TCE at contaminated sites is commonly carried out by dehalorespiring bacteria that utilize these compounds as terminal electron acceptors, but often results in the accumulation of cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC), rather than non-toxic ethene. This project focused on evaluating how interactions among dehalorespiring populations that may utilize the same electron acceptors, electron donors and/or carbon source may affect the extent of PCE dechlorination in situ. These interactions may be particularly important if both Dehalococcoides ethenogenes (Dhc. ethenogenes) and Dehalobacter restrictus (Dhb. restrictus) are present because these bacteria utilize the same electron donor (H2) and both respire PCE and TCE. However, unlike Dhc. ethenogenes, Dhb. restrictus cannot dechlorinate PCE beyond cDCE. Therefore, the outcome of the population interactions may determine the extent of detoxification achieved. Monod kinetic parameter estimates that describe chlorinated ethene and electron donor utilization by Dhc. ethenogenes and Dhb. restrictus at non-inhibitory substrate concentrations were obtained in batch assays. Substrate inhibition effects on both populations were also evaluated. Highly chlorinated ethenes negatively impacted dechlorination of the lesser chlorinated ethenes in both populations. In Dhc. ethenogenes, cometabolic transformation of VC was also inhibited by the presence of other chlorinated ethenes. PCE and TCE dechlorination by Dhb. restrictus was strongly inhibited by VC. The microbial interactions between Dhc. ethenogenes and Dhb. restrictus was investigated using reactors and mathematical models under engineered bioremediation and natural attenuation conditions. Under engineered bioremediation conditions, Dhc. ethenogenes became the dominant population, and the modeling predictions suggested that the inhibition of Dhb. restrictus by VC was a key factor in determining this outcome. Dechlorination rates by Dhb. restrictus appeared to be affected very little by low acetate concentrations under natural attenuation conditions, giving it an advantage over Dhc. ethenogenes, which requires relatively high acetate concentrations. This study highlighted that substrate interactions among dehalorespiring bacteria can influence their performance and contaminant fate under common bioremediation scenarios. A better understanding of the factors affecting the outcomes of these microbial interactions was achieved, which should aid in the design of successful bioremediation strategies.Item Multiple Audiences and Corporate Disclosure(2007-08-28) Yang, Jing-Wen; Kim, Oliver; Business and Management: Accounting & Information Assurance; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study contributes to literature in three ways: first, it draws a full picture about the determinants of a firm's voluntary disclosure decision; second, it aims at tackling the mixed results found about the relation between competition and disclosure; and third, it shows evidence that it is possible that a firm would change its disclosure behaviors across time. The examination is based on the concept that management's communication could reach out to multiple audiences. While a firm could be concerned about the responses from investors and competitors when deciding disclosure-or-not, union and government could also come into consideration. In addition, how the concern about competitors would affect a firm's voluntary disclosure could depend on different interpretations about competition. Whether a firm is thinking of the abnormal profit that it has earned or the cost advantage that it has possessed, different interpretations about competition result in different predictions about the relation between competition and disclosure, and this could have caused mixed results in previous studies. Measuring a firm's disclosure level by the number of information items disclosed within a year, I found that a firm would disclose less in the face of a union's bargaining power and the litigation threat from outside blockholders. Such concerns are even more salient when it comes to revealing proprietary information. In addition, I found that a larger firm would disclose more information about itself, proprietary or not. Higher incentives for a large firm to give more information might come from both demand and supply of information about it. Furthermore, after controlling for other factors, I only found evidence that supports the argument that less competition (in the sense of market power) would cause less disclosure. The results did not, however, show that a firm facing more competition (in the sense of barriers to entry) would choose to disclose less. Finally, the findings also indicated that a firm's disclosure policy could be not as "sticky" as claimed in previous studies, especially when it comes to disclosing proprietary information. A firm might change its attitudes towards disclosure in the face of different political environment.