Theses and Dissertations from UMD
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Item THE EFFECTS OF LEAF LITTER MANAGEMENT PRACTICES ON OVERWINTERING INSECT COMMUNITIES AND ECOSYSTEM FUNCTION: IMPACTS AND APPLICATIONS IN RESIDENTIAL LANDSCAPES(2024) Ferlauto, Max; Burghardt, Karin T; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fallen leaf management is a widespread landscaping practice in urban areas that not only influences soil health but also affects the overwintering individuals of subsequent year's aboveground arthropod communities. There has been considerable public and scientific interest in the ecological effects of this disturbance, yet little experimental research making it difficult to provide evidence-based landscaping recommendations to stakeholders. This dissertation aims to narrow this knowledge gap, provide information for the creation of best management practices, and encourage further research on this critical topic. In Chapter 2, I compare spring arthropod emergence in residential areas where fallen leaves were removed or retained across different levels of maintenance intensity. In Chapter 3, I focus on the legacies of long-term leaf removal to soil organic carbon dynamics. And in Chapter 4, I examine the efficacy of alternative leaf management practices—such as shredding and leaf piling—on soil microclimates, arthropod biodiversity, and decomposition rates while exploring if tree canopy diversity mitigated impacts to these ecosystem functions. The results of these three experimental studies were consistent across years and habitat types. Leaf removal reduced the spring emergence of Lepidoptera by about 35-45% and reduced spiders by about 50-67%, altered parasitic wasp community composition, reduced soil moisture and temperature buffering, and ultimately led to legacy effects in the soil of reduced decomposition and soil organic carbon. The context in which leaves were managed also mattered, as unique resources attracted overwintering arthropods more when they were scarce in the environment. Despite the potential for high plant diversity in leaf-managed areas to create ecosystem traps for arthropods, tree diversity actually mitigated some negative effects of fallen leaf disturbance to ecosystem function. Overall, I find that some practices like leaf removal and shredding degrade ecosystem processes while others like piling leaves and planting a diverse tree canopy can support ecosystem services. This dissertation is the first to quantify the ecological impacts of leaf management as an urban disturbance and addresses critical questions necessary for developing urban best management practices.Item MULTISCALE, MULTITEMPORAL ASSESSMENT OF CHIMPANZEE (Pan troglodytes) HABITAT USING REMOTELY SENSED DATASETS(2023) Jantz, Samuel M; Hansen, Matthew C; Geography/Library & Information Systems; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)All four sub-species of our closest living relative, the chimpanzee, are listed as endangered by the International Union for the Conservation of Nature (IUCN), and their populations continue to decline due to human activities. Effective conservation efforts require information on their population status and distribution. Traditional field surveys are expensive and impractical for covering large areas at regular time intervals, making it difficult to track population trends. Given that chimpanzees occupy a large range (2.3 x 106 km2), new cost-effective methods and data are needed to provide relevant information on population status and trends across large geographic and time scales. The objective of this dissertation is to help fill this gap by leveraging freely available and regularly updated remotely sensed datasets to map and monitor chimpanzee habitat across their range. This research begins by first producing annual forest cover and change maps for the Greater Gombe (GGE) and Greater Mahale ecosystems (GME) in western Tanzania using Landsat phenological metrics and machine learning methods. Canopy cover was predicted at 30-meter resolution and the Cumulative Sums (CuSum) algorithm was applied to the canopy cover time series to detect forest loss and gain events between 2000-2020. An accuracy assessment showed the CuSum algorithm was able to detect forest loss well but had more difficulty detecting gradual forest gain events. A total of 276,000 ha (+/- 27,000 ha) of gross forest loss was detected between 2000 and 2020 in the GGE and GME; however, loss was not spread equally among the two ecosystems. The results show widespread forest loss in the GME, contrasted with net forest cover gain in the GGE. Next, the annual forest cover maps, and additional derived variables, were used to train an ensemble model to predict the relative encounter rate of chimpanzee nest sightings in the GGE and GME. Model output exhibited a strong linear relationship to chimpanzee abundances and population density estimated from a recent ground survey, enabling model output to be linearly transformed into population estimates. The model predicted the two ecosystems harbor just over 3,000 individuals, which agrees with the upper limit of population estimates from ground surveys. Most importantly, the model can be applied to annually updated variables enabling the detection of potential population shifts caused by changes in landscape condition. Model output indicates a possible population reduction in portions of the GME, while the GGE is predicted to have increased its ability to sustain a larger population. Finally, Random Forests regression was used to relate predictor variables, primarily derived from Landsat data to a coarse resolution, range-wide habitat suitability map enabling the prediction of habitat suitability at 30 meter resolution. The model showed good agreement with the calibration data; however, there was considerable variation in predictive capability among the four chimpanzee sub-species. Elevation, Landsat ETM+ band 5 and Landsat derived canopy cover were the strongest predictors; highly suitable areas were associated with dense tree canopy cover for all but the Nigeria-Cameroon and Central Chimpanzee sub-species. The model can detect changes in suitability to support monitoring and conservation planning across the chimpanzee range. Results from this dissertation highlight the promise of integrating continuously updated satellite data into habitat suitability models to detect changes through time and inform conservation efforts for chimpanzees at multiple scales.Item Elucidating factors to improve biological control of Halyomorpha halys by egg parasitoids(2023) Potter, Madeline Elizabeth; Shrewsbury, Paula M; Burghardt, Karin T; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Halyomorpha halys Stål (Hemiptera: Pentatomidae), also known as the brown marmorated stink bug, is an invasive species from Northeast Asia, which has now spread to 47 USA states and invaded several other countries. In the USA, H. halys is an economically important pest of fruit, vegetable, field, and nut crops, and it feeds on ornamental plants. A sustainable means of controlling this pest is needed. Here I focus on elucidating features from bottom-up forces (alternate host identity, host plant identity, and habitat type) which may influence top-down forces such as parasitism by H. haly’s key natural enemies, Hymenoptera egg parasitoids. Naturally laid eggs of insects were collected from a tree nursery in 2020 and from diverse habitats throughout Maryland in 2021 to investigate H. halys parasitoids’ alternate insect egg hosts, host plant and habitat associations, and which factor(s) (host plant identity and/or host egg identity) are important to egg mass discovery, or to egg parasitism rate. Effects of host insect feeding guild (herbivore vs predator) and host plant origin (native vs non-native) on parasitism were also examined. One new overwintering insect host and four new in season hosts for Anastatus spp., and five new in season hosts for Telenomus cristatus were found. A diverse array of plant species, particularly native Acer and Quercus species, were found to support alternate host insects. Halyomorpha halys related parasitoids were reared from eggs collected in all habitat types. Host egg order and egg feeding guild affected Anastatus spp. egg unit discovery efficiency and egg parasitism rate. Host plant identity and plant origin affected egg unit discovery efficiency and egg parasitism rate by all H. halys parasitoids. These findings support the importance of having a diverse community of alternate prey and informed plant selections to support parasitoids and their biological control of H. halys and other insect pests.Item MOVING THE GOALPOSTS: MIGRATORY BIRDS IN A CHANGING WORLD(2023) Nemes, Claire E.; Cohen, Emily B; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Billions of birds undertake migratory movements each year, traveling distances that range from several hundreds to tens of thousands of kilometers. Migratory birds must be flexible enough to cope with the fluctuating conditions they encounter during these journeys and at their destinations. However, humans are rapidly and dramatically changing the environment across all portions of migratory species’ ranges through habitat destruction and conversion, introduction of invasive species, climate change, and other alterations. My dissertation research seeks to understand the constraints and threats facing birds during two understudied phases of the annual cycle: migration and the non-breeding stationary period. In Chapter 1, I explore how human activities may nonlethally affect birds during migration. I reviewed the scientific literature for evidence of nonlethal effects and of interacting threats that may compound fitness costs to migrating birds. In general, I found that scientific understanding of nonlethal effects during migration lags behind research on direct mortality. Because birds migrate through increasingly anthropogenic landscapes and airspaces, I identify this knowledge gap as a hindrance to effective conservation of migratory birds. In Chapter 2, I investigate if individual songbirds adjust the rate and timing of spring migration based on the vegetation phenology they encounter within North America which may allow them to keep pace with advancing spring phenology under climate change. In the spring, migrating birds must quickly reach their breeding grounds to secure territories and mates ahead of the competition, but individuals that arrive too early may encounter inclement weather or food shortages. Using the Motus automated radio telemetry network, I tracked individual songbirds as they traveled from the southern U.S. towards their breeding areas in spring. I used estimates of spring onset timing at different points on their migration routes to determine if birds traveled in sync with the “green wave” of emerging vegetation or if they used a different strategy. I found that birds migrating from their non-breeding areas arrived in the southern U.S. well after local spring onset, but were able to catch up to the wave of emerging spring vegetation as they traveled northwards, following a “catching up” strategy rather than a “surfing” one. In Chapter 3, I examine how individual songbirds respond to the threat of predation during migratory stopover, when they must balance conflicting demands of refueling and avoiding predators. Migrating birds must contend with both native avian predators such as hawks (Accipiter sp.) and abundant introduced predators such as free-roaming domestic cats (Felis catus), yet their behavioral responses to cats have been little studied during migration. Using an aviary experiment, I exposed wild Gray Catbirds Dumetella carolinensis to either a hawk or a domestic cat and observed their behaviors before and after exposure to determine if they responded appropriately to the threat posed by each predator. When compared with a control group, Catbirds responded differently to both types of predators in the short term, but I detected no differences in their behavior after release. This study provides novel insights into the possible nonlethal effects of introduced predators that birds may encounter during migration. In Chapter 4, I shift focus to explore the threat that free-roaming domestic cats pose to birds in the Caribbean within a Neotropical city. Urban regions are increasingly recognized to provide valuable wildlife habitat but may also contain hazards such as introduced predators, and we currently lack information on the effects of free-roaming cats on migratory and resident bird species during non-breeding seasons. I designed a camera trapping project in San Juan, Puerto Rico to estimate free-roaming cat densities across a gradient of urbanization as a step towards understanding their potential impacts on wildlife. I deployed cameras across 16 trapping grids at three levels of urbanization and used photographic captures of cats to build spatial capture-recapture models. Estimated cat densities ranged from 48 8 (SE) cats/km2 in exurban areas to 473 40 cats/km2 in the most heavily urbanized parts of the city. These data may prove useful for conservation practitioners in San Juan deciding where to target cat management efforts for the benefit of urban wildlife and public health.Item LONG-TERM IMPACTS OF AMAZON FOREST DEGRADATION ON CARBON STOCKS AND ANIMAL COMMUNITIES: COMBINING SOUND, STRUCTURE, AND SATELLITE DATA(2020) Rappaport, Danielle I; Dubayah, Ralph; Morton, Douglas; Geography; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Amazon forest plays a vital role in the Earth system, yet forest degradation from logging and fire jeopardizes carbon storage and biodiversity conservation along the deforestation frontier. Polices to reduce forest carbon emissions (REDD+) will fall short of their intended goals unless carbon and biodiversity losses from forest degradation can be monitored over time. Emerging remote sensing tools, lidar and ecoacoustics, provide a means to monitor carbon and biodiversity across spatial, temporal, and taxonomic scales to address data gaps on species distributions and time-scales for recovery. This dissertation draws from a novel multi-sensor perspective to characterize the long-term ecological legacy of Amazon forest degradation across a 20,000 km2 landscape in Mato Grosso, Brazil. It combines high-density airborne lidar, 1100 hours of acoustic surveys, and annual time series of Landsat data to pursue three complementary studies. Chapter 2 establishes the bedrock of the investigation by using fine-scale measurements of structure sampled across a large diversity of degraded forests to model the initial loss and time-dependent recovery of carbon stocks and habitat structure following fire and logging. Chapter 3 models the interactions between sound and structure to predict acoustic community variation, and to account for attenuation in dense tropical forests. Lastly, Chapter 4 uses sound to go beyond structure to identify the specific degradation sequences and pseudo-taxa that give rise to variation in the ‘acoustic guild’ over time. Soundscapes reveal strong and sustained shifts in insect assemblages following fire, and a decoupling of biotic and biomass recovery following logging that defy theoretical predictions (Acoustic Niche Hypothesis). The synergies between lidar and acoustic data confirm the long-term legacy of forest degradation on both forest structure and animal communities in frontier Amazon forests. After multiple fires, forests become carbon-poor, habitats become simplified, and animal communication networks became quieter, less connected, and more homogenous. The combined results quantify large potential benefits to protecting already-burned Amazon forests from recurrent fires. This dissertation paves the way for greater integration of remote sensing and analysis tools to enhance capabilities for bringing biomass and biodiversity monitoring to scale. Building on this research with species-level and multi-temporal measurements will reduce uncertainty around the breakpoints that drive carbon and biodiversity loss following degradation.Item Understanding Conservationists' Perspectives Concerning the Ethical Dilemmas Associated with Declines in African Vulture Populations(2018) Yee, Natalie; Harrell, Reginal M; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Several African vulture populations are declining due to anthropogenic causes. This research explored viewpoints of conservationists to identify ethical dilemmas and extrapolate potential solutions that balance the needs of African vultures and the welfare of impacted societies. The methodology consisted of two parts: A Q-Methodology activity and a semi-structured interview. The Q-Methodology activity used statements in a ranked system to discover what the participants prioritized. The semi-structured interview allowed for an in-depth understanding as to why the respondents ranked the statements as they did. These steps addressed not only what the subjects believed, but why they believed it, a key element in uncovering the ethical standpoints of the respondents. One major finding demonstrated that overall, participants held a deontological (duty-driven) viewpoint that fuels them to pursue conservation work. Exploring views of conservationists familiar with the African vulture declines is the first step to creating ethical policies to save the vultures.Item SOCIAL STRUCTURE OF ASIAN ELEPHANTS (ELEPHAS MAXIMUS) IN SRI LANKA(2015) Samy, Julie Marie; Wilkinson, Gerald S; Thompson, Katerina; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Asian elephants (Elephas maximus) are critically endangered and live in fragmented populations spread across 13 countries. Yet in comparison to the African savannah elephant (Loxodonta africana), relatively little is known about the social structure of wild Asian elephants because the species is mostly found in low visibility habitat. A better understanding of Asian elephant social structure is critical to mitigate human-elephant conflicts that arise due to increasing human encroachments into elephant habitats. In this dissertation, I examined the social structure of Asian elephants at three sites: Yala, Udawalawe, and Minneriya National Parks in Sri Lanka, where the presence of large open areas and high elephant densities are conducive to behavioral observations. First, I found that the size of groups observed at georeferenced locations was affected by forage availability and distance to water, and the effects of these environmental factors on group size depended on site. Second, I discovered that while populations at different sites differed in the prevalence of weak associations among individuals, a core social structure of individuals sharing strong bonds and organized into highly independent clusters was present across sites. Finally, I showed that the core social structure preserved across sites was typically composed of adult females associating with each other and with other age-sex classes. In addition, I showed that females are social at all life stages, whereas males gradually transition from living in a group to a more solitary lifestyle. Taking into consideration these elements of Asian elephant social structure will help conservation biologists develop effective management strategies that account for both human needs and the socio-ecology of the elephants.Item Investigation of spermatozoal metabolism and substrate utilization in domestic and non-domestic felids(2015) Weiner, Halli Sigal; Keefer, Carol L; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Cryopreservation of spermatozoa is a critical aspect of assisted reproduction. However in most cases, this process causes diminished spermatozoal function and low cellular survival. The effects of cryopreservation are further compounded in spermatozoa from individuals with disorders known to affect fertility. Teratospermia, characterized by the ejaculation of >60% morphologically abnormal spermatozoa, is one such disorder. Sperm from individuals with this condition exhibit reduced motility, impaired mitochondrial function, and a reduced ability to bind, penetrate, and fertilize an oocyte compared to sperm from normospermic males. Interestingly, even spermatozoa from teratospermic males that appear normal exhibit reduced functional capacity and following cryopreservation all cells are further impaired. More than 90% of felid species are affected by this condition, and it is prevalent among humans. Previous research suggested that impaired sperm metabolism in cheetahs – a ubiquitously teratospermic species – contributes to their poor cryosurvival and function, but the specific mechanisms are unknown. In this research, we hypothesized that inherent differences exist between the substrates and metabolic pathways utilized by sperm from normospermic and teratospermic individuals and on a species-specific basis. Gas chromatography - mass spectrometry (GC-MS) was used to investigate felid sperm metabolism using semen collected from domestic cats (Felis catus), cheetahs (Acinonyx jubatus), and clouded leopards (Neofelis nebulosa). The main objectives of this research were to: 1) characterize the metabolome of spermatozoa and seminal fluid; 2) investigate the role of β-oxidation in sperm motility and metabolism; and 3) interrogate the significance of specific metabolic pathways using metabolic activity profiling and heavy isotope tracers. Using GC-MS enabled the identification of metabolites which were unique to each species and sperm status (normospermic vs. teratospermic). Additionally, treatment of sperm with a β-oxidation inhibitor caused impaired motility in cheetah - but not domestic cat or clouded leopard - spermatozoa. Finally, fluxomic analysis demonstrated that glucose, fructose, and pyruvate are metabolized by felid sperm, but pathway utilization is species-specific. This is the first study to utilize a metabolomic and fluxomic approach to studying felid sperm, and the results of these studies illustrate the complexity of sperm metabolism on a species-specific basis. Understanding metabolic pathway activity in these cells will aid in the development of improved assisted reproduction techniques that may better facilitate sperm function and survival.Item Greenway as the Framework for Community Design on the Patapsco River Valley(2014) Britt, Nancy Fruchter; Kweon, Byoung-Suk; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)By the nature of their shared locality, greenway corridors and the communities along them share a unique set of socio-cultural and ecological resources that are rooted in the greenway's landscape form and character. When unified, greenways and surrounding communities foster a sense place that is deeply site specific. This thesis explores the unique characteristics of greenway landscapes, using them as a basis for formulating cohesive design criteria for creating vibrant greenway-adjacent communities. These criteria offer solutions for balancing growth and conservation strategies to guide community design within the framework of the greenway, achieve community and greenway sustainability, and support the integrity of the landscape. Using a site along Maryland's Patapsco River Valley, this thesis demonstrates how these criteria can work towards achieving an ideal community form where design highlights unique site features to create awareness of and support for the greenway context.Item ECOLOGY AND DEMOGRAPHY OF GOLDEN-HEADED LION TAMARINS (Leontopithecus chrysomelas) IN CABRUCA AGROFOREST, BAHIA STATE, BRAZIL.(2010) Oliveira, Leonardo de Carvalho; Dietz, James M; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Understanding how species use the matrix of habitat that surrounds forest fragments can contribute to conservation strategies in fragmented landscapes. In this dissertation, I evaluate the effects of habitat structure and resource availability on group characteristics, use of space, and predation risk for the endangered golden-headed-lion tamarins in shaded cocoa plantations locally known as cabruca agroforest. In the first chapter I present a list of tree species that provide key foods and sleeping sites used by lion tamarins. Families Myrtaceae and Sapotaceae are the most commonly used by lion tamarins for both food and sleeping sites. Fifty-five tree species were ranked as extremely valuable for the tamarins. Cabruca management that retains the species listed in this study may improve the long-term survival of lion tamarins. In the second chapter, I compare ecological and demographic data of lion tamarins in cabruca and other vegetation types. In contrast with my prediction that food resources would be scarce in cabruca, the exotic and invasive jackfruit (Artocarpus heterophyllus) was an abundant food resource for tamarins in cabruca while bromeliads were the favorite substrate for animal prey foraging. Group size and composition were similar in all vegetation types. Males in cabruca were heavier than those in primary forest. Density of lion tamarins in cabruca was the highest and home range size the smallest reported for the species. This is the first study to show that lion tamarins can live and reproduce exclusively in cabruca and has important implications for conservation of the species. In my third chapter, I test two hypotheses explaining the association between lion tamarins and Wied's marmoset (Callithrix kuhlii): foraging benefits and predation avoidance. I found no evidence to support the hypothesis that interspecific associations provide foraging benefits for lion tamarins. However, several findings support the predation avoidance hypothesis: associations occurred in areas where predation risk was higher, and during the part of the day in which predation risk was highest, and following birth events when the tamarins were more susceptible to predation. Despite the importance of cabruca to lion tamarins, they are more exposed to predation in this habitat.