MEES Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/19655

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    IMPACTS OF WEIGHTING SCHEMES AND TRANSFORMED ENVIRONMENTAL VARIABLES ON BIODIVERSITY MODELING WITH PRESENCE-ONLY DATA
    (2017) Pradhan, Kavya; Fitzpatrick, Matthew C; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Biodiversity modeling techniques at the community- and species-level can be used to address questions in ecology, management, and conservation. I addressed aspects of community-level and specie-level models using virtual and inventoried species in North and South America. Firstly, I assessed the effectiveness of two weighting schemes in reducing impacts (if any) of five sampling routines (simulating unrepresentative sampling in presence-only data) on the model performance of Generalized dissimilarity model (GDM). Unrepresentative sampling lowers model performance, but weighting species can reduce this negative impact to a certain extent. However, PO data severely impacts GDM’s ability to detect the relative contribution of environmental gradients. Secondly, I examined the potential of (GDM) transformed environmental variables in improving the performance of Maxent models (presence-only) along with the influence of range size, sample size, and species dependence type. Transformed environmental variables improved model performance, especially when used with small-ranged species and/or low sample sizes.
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    Effects of the thermal effluent from C.P. Crane Generating Station on submersed aquatic macrophyte communities in the Saltpeter-Dundee Creek system
    (2007-08-13) Beser, Todd M.; Engelhardt, Katia; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    While water quality is often cited as the main factor that controls the distribution of submersed aquatic macrophytes (SAM) in the Chesapeake Bay, additional factors associated with physical and/or biological disturbances also affect the distribution. At local scales, such as in Saltpeter Creek, a tributary to the Gunpowder River, the thermal effluent from C.P. Crane Power Plant may be an important environmental gradient. I mapped the temperature signature of the effluent in Saltpeter Creek and intensively sampled the plant community structure to investigate the ecological similarity of SAM communities within and across different thermal regimes. I also conducted growth chamber experiments to study how different species and populations sampled from different temperature regimes respond to a controlled temperature gradient. Analyses show that although significant differences in water temperature exist across the study site, differences in temperature do not appear to significantly drive the plant community composition of the system.