College of Agriculture & Natural Resources
Permanent URI for this communityhttp://hdl.handle.net/1903/1598
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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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 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 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.