UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
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 given thesis/dissertation in DRUM.
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Item Cause, consequence, and prevalence of spatial structure of white perch (Morone americana) populations in the Chesapeake Bay(2008-12-11) Kerr, Lisa A.; Secor, David H.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Partial migration defines the simultaneous occurrence of migratory and resident groups within populations. Using otolith chemistry (strontium:calcium measures), I documented partial migration for an estuarine-dependent white perch (Morone americana) population in the Patuxent River estuary (Chesapeake Bay, MD). Previous research indicated that as juveniles, a portion of the population remained resident in freshwater natal habitats and another portion dispersed down-estuary into brackish water habitats. I established these behaviors are alternative life history tactics that persist over the lifetime of individuals. Through back-calculation of hatch-dates, juvenile contingents were associated with their respective larval cohorts, indicating that spatial structuring was influenced by time of spawning, and temperature and prey conditions experienced during early life history. Dispersive individuals originated primarily from earlier spawned larval cohorts, characterized by slower growth and higher mortality rates compared to later spawned cohorts, which contributed disproportionately to the resident contingent. Laboratory experiments revealed that partial migration was associated with varying energetic tactics, with dispersive contingent fish exhibiting higher consumption and faster growth rates subsequent to migration. The prevalence of contingent behavior within other white perch populations in Chesapeake Bay was explored using otolith stable isotope (δ18O) values, which had a positive relationship with salinity and together with otolith δ13C serve as a proxy for regional habitats distributed along an estuarine salinity gradient. Resident contingent fish dominated Upper Bay and Potomac River populations, whereas the dispersive contingent dominated within the Choptank, Nanticoke, James, and York Rivers. The consequences of spatial structuring to productivity (spawning stock biomass), stability (variance in spawning stock biomass), and resilience (years to rebuild the population) of white perch populations were examined using an age-structured simulation model. Increased representation of migratory fish resulted in increased population productivity and resilience, whereas presence of the resident contingent within the population contributed to stability. Increased population stability and productivity also occurred when the abundance of the two contingents varied inversely to one another over time (i.e., asynchronous dynamics). The different roles contingents play in mediating population dynamics and long-term persistence highlights the importance of managing for conservation of spatial structure within fish populations.Item U. S. Households Consumption, A Comprehensive Analysis(2007-02-07) Ding, Li; Sanders, Seth; Economics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Consumption is perhaps the most important economic behavior of human beings. To it goes the lion's share of the country's annual product. This study is part of the ongoing efforts to give a reasonable description of how various factors affect household consumption decision. Those factors include the household's income, demographic characteristics, age structure, cohort characteristics, and commodity prices. The study starts with a cross section analysis based on a sample of about 5,000 households in 2000 U.S. Consumer Expenditure Survey (CES) to look at how income, demographic variables, and age structure affect the household's consumption decision. In the second step, 15 years of CES data (from 1986 to 2000) is used to construct 62 cohorts of households by the birth year of the head of the household, and then examine the impact of age, cohort, and year on the household's spending pattern. In the third and final step, the price effects are examined within the framework of a system of time series equations, incorporating results from the previous two steps. This study enriches the current literature of consumption economics in two aspects. Firstly it builds a linkage so that the information of consumption behavior at household level is summarized into one variable which becomes one of the key determinants to personal consumption expenditure at macro level. Secondly it constructs a set of cohort data and lay out a framework where the changes of consumption patterns caused by generation effects can be examined. The dissertation is organized into five chapters. Following introduction in Chapter 1, Chapter 2 describes the cross section analysis of U.S. Household consumption pattern. Chapter 3 examines the issue from a cohort perspective. Chapter 4 builds the system of demand equations in time series and estimates the model. Chapter 5 concludes the study and explores possible directions for future work.