Theses and Dissertations from UMD
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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
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Item Using a Combination of Phylogenetic Comparative and Paleobotanical Methods to Elucidate Patterns of Lineage Selection in Rosales (Plantae: Anthophyta)(2016) Simpson, Andrew Gordon; Fenster, Charles B.; Wing, Scott L.; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)An increasing focus in evolutionary biology is on the interplay between mesoscale ecological and evolutionary processes such as population demographics, habitat tolerance, and especially geographic distribution, as potential drivers responsible for patterns of diversification and extinction over geologic time. However, few studies to date connect organismal processes such as survival and reproduction through mesoscale patterns to long-term macroevolutionary trends. In my dissertation, I investigate how mechanism of seed dispersal, mediated through geographic range size, influences diversification rates in the Rosales (Plantae: Anthophyta). In my first chapter, I validate the phylogenetic comparative methods that I use in my second and third chapters. Available state speciation and extinction (SSE) models assumptions about evolution known to be false through fossil data. I show, however, that as long as net diversification rates remain positive – a condition likely true for the Rosales – these violations of SSE’s assumptions do not cause significantly biased results. With SSE methods validated, my second chapter reconstructs three associations that appear to increase diversification rate for Rosalean genera: (1) herbaceous habit; (2) a three-way interaction combining animal dispersal, high within-genus species richness, and geographic range on multiple continents; (3) a four-way interaction combining woody habit with the other three characteristics of (2). I suggest that the three- and four-way interactions represent colonization ability and resulting extinction resistance in the face of late Cenozoic climate change; however, there are other possibilities as well that I hope to investigate in future research. My third chapter reconstructs the phylogeographic history of the Rosales using both non-fossil-assisted SSE methods as well as fossil-informed traditional phylogeographic analysis. Ancestral state reconstructions indicate that the Rosaceae diversified in North America while the other Rosalean families diversified elsewhere, possibly in Eurasia. SSE is able to successfully identify groups of genera that were likely to have been ancestrally widespread, but has poorer taxonomic resolution than methods that use fossil data. In conclusion, these chapters together suggest several potential causal links between organismal, mesoscale, and geologic scale processes, but further work will be needed to test the hypotheses that I raise here.Item THE EXCHANGE OF EASTERN OYSTER (CRASSOSTREA VIRGINICA) LARVAE BETWEEN SUBPOPULATIONS IN THE CHOPTANK AND LITTLE CHOPTANK RIVERS: MODEL SIMULATIONS, THE INFLUENCE OF SALINITY, AND IMPLICATIONS FOR RESTORATION(2015) Spires, Jason Eugene; North, Elizabeth; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With limited funds available for restoration and management, information is needed that would enhance the objectives of restoration of the eastern oyster (Crassostrea virginica) in Chesapeake Bay. One challenge with choosing locations for C. virginica restoration is lack of information regarding larval exchange, which helps determine whether the reefs will be self-sustaining and/or enhance nearby populations. The goal of this research was to estimate the larval exchange between subpopulations within the Choptank and Little Choptank Rivers (Maryland, USA) and to determine the influence of low salinity on these patterns in connectivity. To this end, the Lagrangian TRANSport model (LTRANS) was coupled with a Regional Ocean Modeling System hydrodynamic model of Choptank River (ChopROMS) and applied to predict the exchange of simulated C. virginica larvae between 596 reefs within the system. Model results indicated that there is a high degree of connectivity among the subpopulations in this system. Most simulated larvae were transported down river (rather than upriver). Reefs in upper portions of the Choptank River and its tributaries were in a position to produce the most larvae which encountered suitable habitat, whereas those in the lower Choptank River received the most simulated larvae. In addition, salinity-induced mortality of larvae substantially decreased transport success and self-recruitment, and changed patterns in reef-specific transport success throughout the estuary. Model results provide region-specific information that could be used to support restoration efforts in areas with low salinities like the Choptank River.Item CRITICAL PATCH SIZES AND THE SPATIAL STRUCTURE OF SALT MARSH COMMUNITIES(2009) Martinson, Holly Marie; Fagan, William F; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The size, connectivity, and quality of habitat patches can have multifaceted impacts on species and communities. In this dissertation, I combined a multi-year field survey, manipulative field experiments, and a literature review to investigate how spatial structure influences species and their trophic interactions in fragmented habitats. For all empirical work, I used as a study system the arthropod assemblage found on patches of the salt marsh grass Spartina patens. In Chapter 1, I conducted seven surveys of habitat patches over three years to examine the effects of patch size, connectivity, and local environmental conditions on a guild of specialist sap-feeding herbivorous insects and their natural enemies. I found striking differences among species in the effects of both patch size and connectivity, which led to differences in species' relative abundances and trophic structure among these patches. In Chapter 2, I manipulated host plant quality and predator density to experimentally examine mechanisms that might structure this arthropod community. I found that positive responses of herbivores to experimentally-elevated patch quality were limited by dispersal constraints and that predation by abundant generalist spiders may constrain the spatial distribution of certain species. Investigating systems beyond the marsh, I conducted a literature review and analysis in Chapter 3 wherein I examined whether the spatial structure of habitats generally influences trophic interactions. From the literature, I identified 171 studies of trophic interactions in fragmented habitats and found that the influence of fragmentation and related variables on the occurrence or strength of trophic interactions was largely predictable based on the habitat affinity of interacting species. With this dataset, I also identified key gaps in the fragmentation literature, including a heavy bias towards the study of two-species interactions. Therefore, in Chapter 4 I took advantage of my data from the salt marsh to identify how, in addition to the two-species interactions of parasitism and egg predation, more complex food web interactions might depend on variation in the size of habitat patches. Overall, my findings show that variation in patch size can have varied, but predictable, effects on patch occupancy, population density, and interactions between species in fragmented habitats.Item Asocial Monogamy, Extra-pair Paternity, and Dispersal in the Large Treeshrew (Tupaia tana)(2006-04-25) Munshi-South, Jason; Wilkinson, Gerald S; Kleiman, Devra G; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Monogamy occurs in only 5% of mammalian species, but is significantly more common in the Euarchonta: primates, dermopterans, and treeshrews (15% spp.). However, many of these species do not breed monogamously, indicating the need to understand behavioral and genetic monogamy as separate evolutionary phenomena. I examined monogamy in the large treeshrew (Tupaia tana) in Sabah, Malaysia using radiotelemetry data from 46 individuals tracked during and after a fruit masting episode in 1990-1991, during a non-masting period from 2002-2004, and in a selectively logged forest from 2003-2004. I show that large treeshrews exhibit behavioral monogamy in all these ecological situations. However, behavioral monogamy is best characterized as dispersed pair-living, or "asocial monogamy", in this species because male-female pairs travel, forage, and sleep alone on their joint territories. Next, I use microsatellites and mitochondrial DNA d-loop haplotypes to analyze the genetic maternity and paternity of 24 T. tana offspring. I show one of the highest rates of extra-pair paternity (EPP) ever recorded for a behaviorally monogamous mammal. Over 40% of young were sired by males that were not the behavioral partner of their mother, and three litters exhibited evidence of multiple paternity. Comparative analysis of relative testis size in treeshrews and primates indicates that sperm competition is not associated with the high rates of EPP in T. tana, and that the evolution of monogamy is associated with the evolution of smaller testes. Finally, I find genetic evidence of female-biased dispersal and gene flow in large treeshrews. The vast majority of mammals exhibit the behavioral combination of polygyny and male-biased dispersal, but female-biased dispersal may evolve in monogamous species when females compete for ecological resources. In support of the local resource competition hypothesis, I find lower population assignment probabilities and pairwise relatedness for females than males. These results indicate that female T. tana are a mixture of philopatric residents and immigrants from other areas. Coalescent-based Bayesian analyses also show that historical female migration has been three times higher than the overall migration rate between primary and logged forest populations, providing evidence of female-biased gene flow.