Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item How the Availability of Nutrients and Energy Influence the Biodiversity of Cave Ecosystems(2009) Schneider, Katie; Fagan, William F.; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Resource constraints can affect species on multiple levels. In this dissertation, I combine laboratory experiments, an ecosystem-level manipulation experiment and statistical modeling to examine how resources maintain and constrain cave biodiversity and structure cave communities. Chapter I examines how N-limitation may drive morphological adaptations of cave arthropods. By analyzing free amino acid contents, I show that, in comparison to cave-transient millipedes, cave-obligates have decreased concentrations of essential, nonessential and N-rich amino acids, and amino acids associated with pigmentation and cuticular development. Chapter II tests the hypothesis that stoichiometric mismatches impose growth constraints on cave animals. Although results show that cave resource quality is similar to surface leaves, I do show that millipedes experience a strong mismatch to their food. Also, cave-obligate millipedes have lower %P and RNA/DNA (protein synthetic capacity) compared to cave-transient millipedes. Results from these chapters suggest that cave adaptations may reflect stoichiometric challenges of caves. Chapter III describes the manipulation experiment, wherein I removed all organic material from 12 caves, and, while excluding all natural subsidies, I added standardized quantities of leaf packs or rodent carcasses. For 23 months, I monitored the recipient communities to see how subsidies influence species abundance, diversity, and community dynamics. I observed 19,866 arthropods representing 102 morphospecies. Rat treatments supported greater abundances, but the treatments did not differ in richness. Multiple community-level analyses demonstrated that community composition differed drastically depending on treatment. Lastly, the communities changed directionally over time, diverging faster in caves receiving leaves. Chapter IV uses annual bioinventories of 65 caves to investigate occupancy patterns of terrestrial invertebrates. I estimated richness using classical estimators in concert with estimators that incorporate detection. I also used multispecies occupancy models to examine relationships between estimated richness and physical cave characteristics; demonstrating the importance of cave length, entrance geometry (a surrogate for energy input), and connectivity. The results show how inventory data, even if incomplete, can provide valuable information about the distribution of rare species. Resource availability can affect cave ecosystems on multiple levels. Here I illustrate how the biochemical composition, community dynamics, and occupancy patterns of cave species are influenced by resource constraints.Item WTO Accession as Commitment: Theory and Evidence from the Choice of Redistribution Policies(2007-06-05) Chandra, Piyush; Limão, Nuno; Economics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With 150 member countries, and 29 more currently in the process of accession, the World Trade Organization (WTO) is the most important body governing international trade. However, there is little theory on how governments choose between alternative redistribution policies and no work has been done on the role of the WTO in this choice. In this dissertation we develop a theoretical model that explains how a particular set of WTO rules, the Agreement on Subsidies and Countervailing Measures (SCM), affect the choice and the level of tariffs and subsidies -- two of the most important and frequently observed redistribution policies -- in an acceding country. The WTO SCM agreement guides the subsidies that could be used by a member country, as well as, provides other members with retaliatory measures if these subsidies hurt their interests. We show that, as a country joins the WTO, there will be an increase in its tariffs in those sectors that face a threat of retaliation against subsidies. Our model also offers a new explanation for why a country would want to join the WTO. According to our model, the government would like to be a part of the organization since that would increase its utility through an improved bargaining position vis-à-vis the domestic lobbies. We provide a numerical example to illustrate this channel. In the second part of the dissertation we test the prediction of our theoretical model that the sectors, which after accession face a positive probability of retaliation to subsidization, will experience a switch towards tariffs as an alternative instrument of income redistribution. Since Countervailing Duties (CVD) are the most frequently used measure to retaliate against subsidies, we construct a product level database on CVD duties imposed during 1995-2001 by four major users of CVD -- Australia, Canada, the EU, and the US -- and use it to test the above prediction of the model for the case of China's accession to the WTO in 2001 and Taiwan's accession to the WTO in 2002. We use the underlying variation in the way countervailing duties are targeted across different industries to derive a proxy for the threat of retaliation faced by Chinese (Taiwanese) industries at the time of the country's accession to the WTO. We show that in case of both countries accession to the WTO led to a relative increase in tariffs for sectors facing a higher threat of retaliation by CVD. We also show that, as predicted by the model, the increase in tariffs was larger in sectors with higher costs imposed by retaliation.