Theses and Dissertations from UMD
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Item Characterizing tree species diversity in the tropics using full-waveform lidar data(2019) Marselis, Suzanne; Dubayah, Ralph; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tree species diversity is of paramount value to maintain forest health and to ensure that forests are able to provide all vital functions, such as creating oxygen, that are needed for mankind to survive. Most of the world’s tree species grow in the tropical region, but many of them are threatened with extinction due to increasing natural and human-induced pressures on the environment. Mapping tree species diversity in the tropics is of high importance to enable effective conservation management of these highly diverse forests. This dissertation explores a new approach to mapping tree species diversity by using information on the vertical canopy structure derived from full-waveform lidar data. This approach is of particular interest in light of the recently launched Global Ecosystem Dynamics Investigation (GEDI), a full-waveform spaceborne lidar. First, successful derivation of vertical canopy structure metrics is ensured by comparing canopy profiles from airborne lidar data to those from terrestrial lidar. Then, the airborne canopy profiles were used to map five successional vegetation types in Lopé National Park in Gabon, Africa. Second, the relationship between vertical canopy structure and tree species richness was evaluated across four study sites in Gabon, which enabled mapping of tree species richness using canopy structure information from full-waveform lidar. Third, the relationship between canopy structure and tree species richness across the tropics was established using field and lidar data collected in 16 study sites across the tropics. Finally, it was evaluated how the methods and applications developed here could be adapted and used for mapping pan-tropical tree species diversity using future GEDI lidar data products.Item Diversity and structure of Metrosideros polymorpha canopy arthropod communities across space and time(2019) Tielens, Elske Karolien; Gruner, Daniel S; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Global biodiversity is under pressure from climate change, habitat fragmentation and other anthropogenic change, and our ability to predict biodiversity responses to change requires a better understanding of the processes that drive diversity and structure local communities. However, quantifying these processes has proven to be challenging for multiple reasons; diversity is multidimensional, and both diversity and the processes that generate it vary across scale. In this dissertation, I examine temporal and spatial patterns in community structure to test hypotheses about the drivers of local diversity and composition in communities of varying age, focusing on arthropod communities associated with the native tree Metrosideros polymorpha on the Hawaiian Islands. Analysis of Hemiptera (true bug) communities reveals a temporal pattern in community structure, where young substrate communities were variable in species composition and beta dispersion decreased with substrate age, indicating convergence. However, substrate age did not correlate with community dissimilarity in a directional way. Similarly, geographic distance did not correlate with compositional dissimilarity, suggesting a lack of dispersal limitation. I confirmed this result by examining connections between arthropod communities in a historically fragmented ‘kīpuka’ landscape, using species-area relationships and graph theory analyses. Finally, if canopy arthropods are dispersive and differences in species composition across sites are not driven by substrate age, local habitat characteristics may influence species composition. I determined the role of local beta diversity and identified habitat characteristics regarding forest structure and host leaf traits that are strong drivers of beta diversity and species composition. Then, to further explore local habitat drivers I examined forests with high intraspecific variation in co-occurring Metrosideros. In this hybrid zone, insect life history traits shape species’ response to intraspecific variation in host plant characteristics, highlighting the importance of including dimensions of biodiversity beyond taxonomic diversity. Together, these results demonstrate the importance of local habitat conditions for canopy arthropods, suggest that canopy arthropod communities are highly connected and that substrate age plays a limited role in determining local arthropod communities. Such insights into biodiversity and plant-insect interactions across temporal and spatial scale are integral to understanding and conserving our natural world.Item 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.Item Cumulative impacts of stream burial on network structure and functional connectivity in headwater stream systems(2015) Weitzell, Jr, Roy Everett; Elmore, Andrew J; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Stream burial is common during urbanization, and disproportionately affects headwater streams. Burial undermines the physical, chemical, and spatial processes governing aquatic life, with consequences for water quality and biodiversity, both within headwaters and in downstream waters. Network changes associated with headwater burial have not been explored, limiting our understanding of changes in biotic composition with urbanization of these critical ecosystems. To address this need, I predicted stream burial across the Potomac River Basin (PRB) from impervious cover data and training observations from high-resolution aerial photography. Results across the PRB urban gradient reveal consistent burial patterns related to catchment area and topographic slope. I discuss these results in the context of physiographic constraints on stream location and urban development, including implications for management of aquatic resources. Second, I examined burial-related changes to headwater network structure and habitat connectivity, using a series of topological and distance measures, and a novel application of circuit-theoretical modeling to stream networks. Results show stream burial significantly affects both the number and size of remnant stream segments and their spatial orientation. Significant decreases in landscape connectivity were observed with burial, around ecologically important features such as confluences, and for urbanized headwater systems as a whole. Third, I used biological data to compare environmental and spatial controls on species turnover in fish and insect communities across headwater systems. Turnover was analyzed using generalized dissimilarity modeling, which accommodates variation in rates of species turnover along and between gradients, and two novel measures of resistance distance, which combine aspects of space and environment, specifically the spatial extent, orientation, and relative favorability of habitat across the landscape. Results show headwater species are more sensitive to environmental parameters, with less mobile species more sensitive to habitat fragmentation and required dispersal distances. Rapid compositional turnover occurred within short distances from the sampled reaches, suggesting headwater taxa disperse only short distances, with even small obstructions or habitat loss having potential to impact diversity within headwater systems. Knowledge gained from this research is critical for understanding the cumulative impact to stream networks, and for future decision-making allowing for urban development while protecting stream ecosystem function.Item NOVEL APPROACHES TO STUDYING BIODIVERSITY IN REMOTE AREAS: DISTRIBUTION OF LICHENS AND PENGUINS ACROSS THE ANTARCTIC PENINSULA(2013) Casanovas, Paula Victoria; Fagan, William F; Lynch, Heather J; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Biodiversity inventories are a critical resource, providing baseline information for assessing environmental changes over time. In many cases, the underlying datasets are generated by "opportunistic" sampling efforts or they are consolidated from diverse datasets collected for different purposes. These datasets are typically patchy and incomplete, requiring the use of sophisticated statistical analyses. The Antarctic Peninsula (AP) is one of those areas where direct observation of species distribution is difficult; it is also an area that in recent decades has been experiencing important environmental changes, which influence population and ecosystem dynamics. I addressed biogeographical questions in the AP archipelago, using remote sensing and opportunistic data sets for two very different groups of organisms: lichens and penguins. Although taxonomically different, both groups are key components of the AP terrestrial ecosystem, and share the need to couple biodiversity surveys with modeling to understand species distribution and abundance patterns in large areas of remote wilderness. The results of this dissertation work are interesting to polar biologists, because evidence suggests that the input of nutrients by seabirds can significantly impact floral diversity and abundance in nutrient-poor polar communities. The datasets and protocols for data collection and analyses generated in this project are valuable in themselves for the scientific community. They could be used as the basis for a valuable and practicable monitoring program and procedures for the evaluation of the data derived from it. In the Antarctic Peninsula in particular, this information will aid in the delineation and management of protected areas, as well as in the evaluation of the impacts of climate change and human visitation to the most traveled locations. Furthermore, this research provided an example of how an approach that integrates the use of existing remote-sensing products with independent ongoing field sampling efforts, "citizen scientist" data collection, and historical datasets can yield low-cost, high-benefit studies that can be useful both to understand how species respond to their environment, and to help environmental managers to predict and cope with imminent changes due to global warming.Item Diversity, Invasibility, and Resource Use in Marine Fouling Communities of San Francisco Bay(2011) Altman, Safra; Reaka, Marjorie L; Hines, Anson H; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Invasive species threaten the biodiversity of estuaries worldwide. To examine the relationships between biodiversity, invasibility, and invasion success, I conducted field surveys and experiments in San Francisco Bay marine fouling communities, including 1) surveys to estimate alpha, gamma, and beta diversity of native, non-native and cryptogenic components of the community; 2) experiments to assess the influence of diversity and resource availability on short-term recruitment of novel non-indigenous species (NIS) into test communities and subsequent community development over time; and 3) an experiment to explore the role of facilitative interactions of NIS in the diversity-invasibility relationship. Surveys (10-24 sites) showed that non-native alpha diversity was significantly greater than native or cryptogenic alpha diversity, beta diversity was significantly greater for native and cryptogenic species than for NIS, and gamma diversity was similar for NIS and native species. These results indicate that native species had high turn over from site to site while NIS were spread throughout the Bay. Experiments showed that on short time scales (2-4 weeks), the effect of initial diversity on the density of recruitment of NIS was significant and negative, with no effect of resource level (increased open space). Changes in community composition over time (2-24 weeks) also indicated significant inverse relationships between percent cover of NIS and diversity of the initial community with no evidence of a resource effect. Abundant NIS occupied less space in communities with higher initial diversity. However, the same NIS occupied (i.e., had invaded) all experimental communities regardless of starting diversity. Additional experiments revealed that recruitment to secondary substrates did not vary significantly with invasive species diversity or resource availability. When total recruitment to primary and secondary substrates were combined, there was no longer a significant relationship between diversity and recruitment. Analysis of secondary settlement patterns revealed that some NIS, such as Bugula neritina, were facilitating recruitment and settlement of additional NIS. In contrast, other species, such as Clathria prolifera and Botryllus schlosseri, inhibited secondary settlement of NIS. The influence of diversity and primary resource availability on secondary settlement did not appear to affect settlement on facilitative species, but reduced settlement on inhibitive species.Item 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.Item Correlates of Terrestrial Vertebrate Species Richness: an Evaluation of Environmental Hypotheses over the Western Continental USA(2006-04-24) Slayback, Daniel Andrew; Prince, Stephen D; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)An explanation for the unequal distribution of life forms across the Earth's surface has been a persistent and problematic question in modern ecology ever since these patterns were first noted, over 100 years ago. Most empirical research supports one of three environmental hypotheses to explain these patterns: environmental energy (ambient environmental energy or ecosystem productivity); climatic variability; or habitat heterogeneity. This research examines these hypotheses using better datasets than those commonly considered, and using a consistent methodology that addresses often neglected statistical and analytic details. The environmental datasets used in this study are derived from time series of satellite and ground station data, including the Daymet climate data, and net primary productivity data from the GLOPEM model. Species richness is derived from the individually modeled vertebrate distributions provided by the individual state Gap Analysis Projects for the western US states of California, Oregon, Washington, Idaho, Montana, Wyoming, Utah, and Colorado, which define the spatial extent of this study. The study methodology relies upon the summary of results from many model variants for each hypothesis. These variants are constructed by creating regression models at each of four different spatial scales (8, 16, 32, and 64 km grid cells), for each class of vertebrates (amphibians, birds, mammals, reptiles, and all), and over each of the eight states considered. Preliminary studies found that ordinary least squares would be a sufficient model form, although conditional autoregressive models were extensively considered. Other preliminary work examined issues of spatial autocorrelation and variable selection. The results indicate that the energy/productivity hypothesis consistently outperforms all other hypotheses in explaining species richness, across almost all spatial scales, geographic regions, and vertebrate classes. The performance of the climatic variability and habitat heterogeneity hypotheses varies for particular states or vertebrate classes. Vertebrate data quality was important; results for Colorado and Washington were frequently unusual, suggesting an incompatibility between their modeled vertebrate distributions and those of other states. Models of reptile richness also often showed substantially different characteristics than those for other vertebrates. Overall the results provide additional support to the energy/productivity hypothesis, from a more comprehensive methodological basis.Item Predator diversity, habitat complexity and the strength of terrestrial trophic cascades(2005-04-15) Finke, Deborah Lee; Denno, Robert F; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Food web complexity is thought to weaken the strength of terrestrial trophic cascades whereby strong natural enemy impacts on herbivores cascade to indirectly influence primary production. Predator diversity can enhance food web complexity by promoting the occurrence of intraguild predation, wherein predators feed on each other and on shared prey. In such cases, theory suggests that the impact of predation on herbivores relaxes and cascading effects on basal resources are dampened. In a terrestrial marsh community, I compared arthropod predator impacts on herbivores and plant productivity between a simple food web with a single predator species and a complex food web with a diverse predator assemblage. I found that enhancing predator diversity dampened enemy effects on herbivores and weakened trophic cascades. The role of intraguild predators in dampening such trophic cascades was determined by factorially manipulating predator species richness (1, 2, or 3 species) and predator trophic composition (strict predators, intraguild predators, or a mixture of both) and measuring their effects on prey suppression and plant productivity. I found that the impact of predator richness on the strength of trophic cascades was dependent on the trophic composition of the predator complex present. Specifically, strict predators additively enhanced planthopper suppression and increased plant productivity with an increase in species richness. However, intraguild predators interacted antagonistically, resulting in greater herbivore abundance and lower plant productivity at the highest levels of species richness. An investigation of the influence of habitat complexity on cascading predator effects revealed that complex habitats with cordgrass leaf litter provided a refuge for predators from intraguild predation and elevated planthopper suppression by the diverse predator assemblage. However, reducing the antagonistic predator-predator interactions and increasing prey suppression did not enhance the conductance of predator effects through the food web to impact positively primary producers, although there was a trend towards greater plant biomass in the complex-structured habitat. Therefore, the possibility exists that changes in habitat complexity might enhance trophic cascades and impact positively productivity by mediating trophic interactions among predators. Overall, interactions between species diversity at higher trophic levels and habitat structure can significantly alter ecosystem function in natural systems.