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.
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
3 results
Search Results
Item LEATHERBACK TURTLE MOVEMENT AND DISPERSAL FROM NESTING BEACHES IN COSTA RICA WITH IMPLICATIONS FOR MANAGEMENT AND CONSERVATION(2017) Hoover, Aimee Lynn; Bailey, Helen; Secor, David H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Electronic tagging permits movement and distribution studies of sea turtles as they traverse large distances through a dynamic ocean environment. However, little is known about the movements of early life stages at sea, a period termed the 'lost years'. I developed and tested a method for attaching an acoustic tag suitable for use on leatherback turtles that was then applied to hatchlings in Costa Rica to obtain measures of speed and directionality. This was compared with ocean currents and revealed that the hatchlings actively swam against nearshore currents, although they were still advected by them. Finally, a Poisson generalized linear model in a continuous-time Markov chain model framework was used to predict adult, post-nesting Eastern Pacific leatherback movement based on environmental drivers, such as sea surface temperature. Monthly, near real-time predictions of leatherback movement were estimated using the most recent satellite-derived environmental information to help inform conservation management strategies.Item Avian community responses to ecological disturbance and recovery at Mount St. Helens, WA, USA(2013) Larsen, Elise A.; Fagan, William F.; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Community assembly occurs through the complex interaction of local and regional processes which contribute to the differential colonization and extinction of species within a local site. Understanding these processes is of fundamental importance to ecology because it enables predictions for the trajectory of recovery in ecological systems following disturbance. In this dissertation I combined field studies of the Mount St. Helens bird community with historical and regional data to better understand the processes contributing to local assembly in a mainland community following large scale volcanic disturbance. First, I applied a novel spatial approach to examine avian colonization patterns at Mount St. Helens and approximate the geographic extent of the region influencing local community assembly in the first thirty years of recovery. Despite the prevalence of regional sources, avian colonization of Mount St. Helens has occurred slowly over thirty years. By approximating `minimum source regions' for local communities across time, I developed a new approach for examining the spatiotemporal dynamics of colonization and found that species from a broad geographic area extending beyond the Cascade mountains have colonized Mount St Helens. I then focused on the primary successional habitat of the Mount St. Helens Pumice Plain to examine what ecological processes have contributed to avian community assembly. Testing multiple assembly hypotheses I found evidence of niche-based assembly through nestedness and habitat filtering but no support for competition-based assembly rules. Finally, I addressed the specific mechanism of local recruitment in maintaining populations of birds on the Pumice Plain by monitoring nest success across species. I found observed nest success lower than previously recorded in other habitats for several common ground-nesting and shrub-nesting species. I determined that in the absence of sufficient local recruitment, repeated colonization from the surrounding region may contribute to the persistence of some species on the Pumice Plain. Overall, my results found evidence of habitat filtering rather than interspecific competition in limiting early assembly and supported the importance of continued colonization processes drawing from a range of regional habitats.Item Local versus regional processes impacting insect diversity loss from urban headwater streams(2012) Smith, Robert Francis; Lamp, William O; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Watershed urbanization alters hydrologic, geomorphic, and chemical properties of stream ecosystems and decreases water and habitat quality for stream fauna. The resulting loss of insect diversity from urban streams and the mechanisms resulting from in-stream habitat degradation are well documented. In this study, I focus on how urbanized terrestrial landscapes contribute to diversity loss from stream insect communities. Characteristics of fragmented urban landscapes likely increase mortality, reduce reproduction, and block dispersal by adult stream insects, which can contribute to reduced diversity. I compared the adult caddisfly assemblage among 4 urban and 4 rural headwater streams and found no difference in abundance but lower taxa richness at urban than rural headwaters. Poor in-stream and terrestrial environmental conditions likely caused decreased adult diversity at urban headwaters. I expanded this study by comparing adult and larval assemblages residing in the same 8 headwater streams. Patterns of larval and adult taxa richness, assemblage composition, and urban landscape structure at individual streams suggested that constrained dispersal through urban landscapes (a regional process) and poor environmental conditions in the stream (a local process) both contributed to larval diversity loss from urban headwaters. I also compared flight morphological characteristics of 2 caddisfly species restricted to rural headwaters to 4 species that commonly immigrated to urban headwaters. Wing length and wing aspect ratio did not differ between these 2 groups, but species specific differences for both measures indicated that flight ability may have supported immigration to urban headwaters for certain species. Finally, I used multimodel inference testing to determine what combination of geographic distance, environmental dissimilarity, and land use between streams best explained patterns of taxonomic dissimilarity between in-stream insect communities within 4 Maryland watersheds. All three variables together, based on Euclidean geographic distance, provided the best model fit and supported the hypothesis that regional and local processes structure stream insect communities simultaneously. The overall conclusion from my work was that site specific characteristics of terrestrial urban landscapes caused species specific constraints on adult insect migration that contributed to larval diversity loss from urban streams simultaneously with poor in-stream habitat and water quality.