College of Agriculture & Natural Resources
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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item ANTHROPOGENIC INFLUENCES ON BOTTOM-UP AND TOP-DOWN REGULATION OF ANIMAL DISTRIBUTIONS, POPULATIONS, AND BEHAVIORS IN URBAN ENVIRONMENTS(2024) Herrera, Daniel Joseph; Gallo, Travis; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Animal populations are simultaneously governed by both bottom-up (e.g., habitat availability) and top-down (e.g., predation) regulation. While ecologists historically sought to differentiate the roles of bottom-up and top-down regulation on ecosystems, the two are not so easily defined in urban ecosystems due to the immense influence humans have on ecological processes in cities. In Chapter One, I present this argument from a philosophical perspective and comment on how this philosophy has shaped my worldview. In Chapter Two, I examine the legacy of historical park planning on urban bird assemblages using archived municipal maps and historical bird data. My analysis found a positive correlation between percent park area and both species richness and functional richness of birds. Additionally, I found the effect size of park area was larger than the effect of certain life history traits thought to facilitate urban exploitation. These results indicate that landscape features and life history traits are equally responsible for the success of synurbic species. Chapter Three explores the effect of urbanization on animal behavior by analyzing anti-predator behavior of white-tailed deer (Odocoileus virginianus) in relation to ambient light, noise, and human activity. Despite negligible predation risk in my study area, deer expressed higher vigilance behavior in dark and noisy conditions, and increased their foraging group size during noisy conditions. These results suggest that anti-predator behaviors are a response to the perception of predation risk rather than a response to the actual presence of predators. Although predation of deer is rare in urban ecosystems, predation of smaller wildlife species by mesopredators, such as non-native domestic cats (Felis catus) is common. Chapter Four examines the potential for predation and zoonotic disease transmission between cats and eight native mammals by estimating the spatial and temporal overlap between species. I found that cat distribution was largely driven by anthropogenic features, whereas native wildlife was generally deterred by anthropogenic features and instead occupied forested areas. I also found that cats, as a species, were active on the landscape during the full 24-hour cycle. As a result, while spatial overlap between cats and wildlife varied across the study area, temporal overlap was possible anywhere cats and wildlife co-occurred. Chapter Five expands on Chapter Four and investigates predation directly by using observations of cats carrying prey documented by motion-activated cameras. I found that predation by cats was higher in areas where supplemental cat food was prevalent, but declined near forested areas. Additionally, my results indicate that cats within 250 meters of a forest edge predominantly preyed on native wildlife, whereas cats generally preyed on non-native rats (Rattus norvegicus) when greater than 250 meters from a forest edge. Each chapter provides applied recommendations to the management and conservation of urban wildlife, but together, my work demonstrates the entanglement of bottom-up, top-down, and anthropogenic forces in urban ecosystems. In light of these findings, I advocate for a more nuanced understanding of ecosystem regulation through a socio-ecological lens.Item OVARIAN STROMAL CELLS IMPROVE SURVIVAL, BUT NOT GROWTH, IN PRE- AND EARLY ANTRAL FELINE FOLLICLES(2024) Marks, Batsheva Naomi; Keefer, Carol; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ovarian stromal cells act as crucial support and regulators for in vivo folliculogenesis; however, less is known about their effect on in vitro grown follicles. The objective of this study was to investigate the impact of ovarian stromal cell co-culture or conditioned medium (CM) on survival and development of cat pre-, early, and antral follicles in vitro. Ovaries were obtained from cats older than six months (n = 3), then enzymatically digested to release stromal cells. The ovarian stromal cells were allowed to grow to confluency in a T75 flask, before being cryopreserved for long term storage in liquid nitrogen. Cells were thawed one week prior to follicular culture onset, and passaged once before CM collection. CM was subsequently removed 24 - 48 hours after feeding, and stored at -80C until used. Ovarian follicles were mechanically isolated from cats older than six months (n = 23 cats, 155 follicles), encapsulated in 0.5% alginate hydrogel. The isolated follicles were then divided into five treatment groups (control, ovarian stromal cell co-culture, 20% CM, 50% CM, and 100% CM in Endothelial Cell Growth Medium), and classified based on initial diameter as preantral (224.4 + 4.7 m), early antral (394.8 + 7.4 m), or antral (592.2 + 18.8 m). Culture subsequently lasted for 13 days, and survival and growth of the follicles were evaluated on Days 0, 4, 6, 8, 11 and 13. At the end of culture, follicles were assessed via qRT-PCR for expression of CYP19A, FSHR, and GDP9 to further quantify development. Statistical analysis was done in R software. Follicles in 100% CM had higher survival up to Day 11 of culture as compared to other treatment groups (Cox proportional hazards model, p < 0.01). Initial stage also influenced survival, with antral follicle survival significantly lower than that of pre- and early antral follicles (p < 0.0001). However, no differences in growth were detected across the treatment groups, nor across initial size classifications (Kruskal-Wallis test, p > 0.05). Post culture qRT-PCR analysis of the three selected genes showed upregulation of CYP19A in 50% CM follicles compared to the control (ANOVA, p < 0.05). However, there were no differences in CYP19A expression between the control and other treatment groups, or in GDF9 and FSHR expression among culture groups (p > 0.05). In summary, the findings demonstrated that conditioned medium collected from primary culture of ovarian stromal cells improves in vitro survival and modulates CYP19A expression of isolated cat follicles. Further research to identify paracrine factors present in conditioned medium will elucidate the roles of ovarian stromal cells pertaining to follicle survival during in vitro folliculogenesis.Item TO WHAT EXTENT DO MODE OF REPRODUCTION, LEVELS OF GENOTYPIC DIVERSITY, AND CONNECTIVITY IN Vallisneria americana MICHX. CONFER RESILIENCE TO A CHANGING CLIMATE?(2023) Perkins, Carrie; Neel, Maile C.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The macrophyte Vallisneria americana Michx. (Hydrocharitaceae) is a foundational submersed aquatic vegetation (SAV) species that provides valuable ecosystem services, such as nutrition for waterfowl and shelter for fish. When healthy, V. americana can absorb excess nutrients from the water and stabilize sediments, but many of its meadows, which span freshwater to oligohaline environments in eastern North America, have been declining since European settlers cleared the land. Declines only intensified in the 1950s due to chronic environmental stressors and major storm events. To determine the extent to which remaining populations can adapt through natural selection or acclimate to novel environmental conditions, I combined observational field data, greenhouse experiments, and spatial modeling to quantify V. americana reproduction at local to regional scales, evaluate evidence of local adaptation and acclimation to environmental stress, and assess the extent to which high levels of connectivity in a V. americana-dominated landscape can absorb environmental stress.I quantified reproduction at 15 sites in the Chesapeake Bay and 14 sites in the Hudson River, with sites in each geographic region spanning the portion of the salinity gradient in which V. americana grows (0-12 ppt). Numbers of inflorescences, sex ratios, and distances among male and female inflorescences varied greatly across latitude and along salinity gradients. Hudson V. americana had fewer inflorescences across two sampling seasons than Chesapeake Bay V. americana but delayed phenology, skewed sex ratios, and large distances among males and females relative to the Chesapeake Bay were more pronounced in 2018. In 2018, warmer spring and summer water temperatures in the Chesapeake coincided with our findings of higher flowering, fruiting, and potential for pollination at the three Chesapeake sites that served as means of comparison to the Hudson. By contrast, in 2020 Hudson plants were larger and produced more inflorescences in July than Chesapeake plants produced in June, indicating that the regional difference in phenology may be smaller than our hypothesis of approximately 23 days, although it is difficult to estimate how much smaller. We attribute this result to sites in the Hudson – mainly those in the tidal-fresh zone of the river – being highly responsive to unusually warm 2020 spring water temperatures. But not all sites experienced this warmth. The tidal-saline zone of the Hudson and the non-tidal zone of the Chesapeake had the fewest flowers and fruits of either region, likely due to the synergistic effects of cold temperatures and high salinity and turbidity in the former and fast currents in the latter inhibiting growth and reproduction. Through greenhouse experiments evaluating growth and reproduction of Chesapeake and Hudson V. americana grown in different salinity conditions, we found evidence of one-way local adaptation in plants sourced from brackish waters of both the Chesapeake and Hudson. In the first experiment (parental-generation), brackish-source plants demonstrated phenotypic buffering, a stress-induced version of phenotypic plasticity. When exposed to three salinity treatments (0 ppt, 6 ppt, and 12 ppt) applied after plants had sprouted, brackish-source plants buffered the effects of salt stress via increased vegetative growth in the form of many ramets and turions at the cost of small stature. By contrast, plants sourced from fresh waters of both regions grew tall in fresh water, but photosynthetic leaf material declined from the time of salt application (June) to the end of the experiment (September). The most severe salinity treatment, 18 ppt, was lethal to most individuals regardless of source habitat. Unfortunately, neither phenotypic buffering nor phenotypic plasticity sensu stricto was carried over via transgenerational plasticity (TGP), when turions were exposed to 12 ppt immediately upon planting (offspring generation). This early-development salt exposure proved lethal for some individuals and sublethal (had a negative effect on growth but did not result in mortality) for others, with turions either failing to sprout or growing a single shoot that was minuscule in stature. Parental-generation salt exposure only exacerbated these offspring effects, producing a non-adaptive TGP effect, resulting in even lower chance of sprouting, higher chance of mortality, and smaller stature. Evidence of local adaptation and acclimation to salinity only when exposure begins later in development suggests that populations have potential for resilience to saltwater intrusion (movement of saline water into fresh water) only if salinities do not remain elevated during the time of early plant development (spring/early summer) and across multiple seasons. In the event of prolonged salinity stress, much habitat (~10,000 hectares) that is currently mesohaline (5-12 ppt) but within the range of tolerance for V. americana will become unsuitable. In our spatial model of SAV persistence in the V. americana-dominated Upper Chesapeake Bay, high connectivity and high probability of SAV presence were found not only in the freshwater head of the Bay, but also in mesohaline (5-12 ppt) and oligohaline (0.5-5 ppt) waters near Middle River. Persistence of predominantly freshwater aquatic macrophytes in Middle River suggests that either 1) plants are locally adapted to brackish waters or 2) existing connectivity buffers the stress of low-quality habitat. Excess nitrogen, an anthropogenic environmental stressor that remains at high levels in Baltimore Harbor and other tributaries, was correlated with a decreased probability of SAV presence in the southern portion of our study area. As expected, low nitrogen, low salinity, and high landscape connectivity at the head of the Bay coincided with the highest predicted probabilities of SAV presence, particularly in the core of the one of the largest SAV beds in the entire Chesapeake Bay, the Susquehanna Flats.Item Ecological Restoration Drives Functional Composition and Diversity in Urban Forest Patches(2020) Do, Sara Miya; Johnson, Lea R; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Urbanization greatly alters environmental conditions, affecting biodiversity in cities and ecological processes. To restore processes and native biodiversity, land managers have turned to ecological restoration of urban forest patches. Urban forest patches, nested within urban ecosystems, are subject to urban influences during ecological succession. Building on a long-term study evaluating outcomes of ecological restoration in New York City, I examined the effects of urban conditions, restoration, and forest succession on functional composition and diversity of restored and unrestored urban forest patches after 15-20 years. Functional traits play an essential role in community assemblages and influence the resilience and ecosystem functioning of urban ecosystems. I found that restored plots had greater functional evenness. Differences in functional composition indicated direct influence from restoration, succession, urban conditions, and success in meeting restoration goals. These results demonstrate that ecological restoration drives changes in functional composition and diversity of urban forest patches.Item Survival and biochemical health indicators of Elliptio complanata deployed in Anacostia River tributaries for monitoring of persistent organic contaminants(2019) Harrison, Rachel Marie; Yonkos, Lance T; Environmental Science and Technology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Anacostia River is one of three regions-of-concern in the Chesapeake Bay Watershed. Persistent organic pollutants (POPs) such as polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and organochlorine pesticides are known to accumulate in sediment and biota within portions of the Anacostia system, but on-going contaminant sources are poorly understood. The current study investigates relative contaminant burdens in the freshwater mussel Elliptio complanata deployed in six non-tidal Anacostia tributaries and an out-of-system reference site. Mussels acquire contaminants during feeding and are a useful tool for monitoring POPs transporting through the system. Mussels were effective at identifying sites with high contaminant loads. The study also investigates the suitability of Anacostia tributaries for reintroduction of E. complanata to increase benthic community diversity and potentially improve water quality. Survival and growth during deployment was very good for both sampling seasons. Biochemical health parameters of deployed mussels suggest that conditions may be suitable for mussel reintroduction.Item Population Declines and Genetic Variation: Effects of Serial Bottlenecks(2015) Callicrate, Taylor Eilers; Song, Jiuzhou; Fleischer, Robert C; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Islands foster unique biodiversity, yet also present biogeographic limitations that impose increased risk for population extinction through demographic and genetic constraints and decreased probability of surviving a catastrophe. Of particular interest, especially with regard to endangered species, is the genetic response of insular species to severe population declines or translocations. Both types of events, considered population bottlenecks, are expected to reduce genetic variation, and correspondingly, adaptive potential. For these reasons, it is important to understand how bottlenecks interact with insular population dynamics to affect genetic diversity. I used a combination of a laboratory model experiment and population genetics study of an in situ bottleneck in an endangered species to investigate how quantitative and molecular genetic variation are affected during bottlenecks. I used a laboratory animal model (red flour beetle, Tribolium castaneum) to compare how quantitative genetic variation is affected if a serial bottleneck occurs in a novel versus familiar environment. The experiment was designed to model a founder event or translocation to a new island with a novel environment. I found that phenotypic and additive variance for a quantitative trait were larger following a bottleneck occurring in the novel environment, suggesting that the novel environment could improve adaptive potential in bottlenecked populations. Next, I used molecular genetic markers to assess variation and signatures of selection in the Laysan finch (Telespiza cantans), a Hawaiian honeycreeper endemic to a small Northwestern Hawaiian island. Laysan finches experienced a major bottleneck on Laysan in the early 20th century, followed by a translocation and series of founder events as populations were established on the islets of Pearl and Hermes Reef (PHR) in the 1960s – 70s. I found that, contrary to expectation, bottlenecked Laysan finch populations did not show declines in genetic variation and were not differentiated as a result of genetic drift. These results are potentially caused by insular demographic dynamics. I identified loci with extreme differentiation between modern populations, potentially indicating genomic signals of selection. These regions could be important for adaptation to the novel environment on PHR and are candidates for future study.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 CHARACTERIZATION, ENRICHMENT, AND IN VITRO CULTURE OF SPERMATOGONIAL STEM CELLS IN THE DOMESTIC CAT: A MODEL FOR RARE AND ENDANGERED FELIDS(2014) Vansandt, Lindsey Marie; Keefer, Carol L; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Spermatogenesis is a highly prolific process in which millions of spermatozoa are produced daily. Spermatogonial stem cells (SSCs), the adult stem cell population of the testis, sustain this process by providing a constant source of new progenitor cells. The ability of this stem cell population to self-renew makes it a promising alternative to spermatozoa for genetic preservation of rare and endangered animals. While innovative advances in SSC technologies have been made in the mouse, there is a paucity of information concerning felid SSCs. Therefore, the overall objective of the dissertation was to develop SSC technology in the domestic cat (Felis catus) as a model for rare and endangered felids. In the first study, mRNA transcripts for six SSC marker genes (THY1, GPR125, GFRalpha1, PLZF, UCHL1, and OCT4) were identified in cat testes. Localization within the appropriate in situ niche was confirmed by immunohistochemistry for three of the markers (PLZF, UCHL1, and OCT4). The expression pattern of these markers was conserved in the cheetah (Acinonyx jubatus) and Amur leopard (Panthera pardus orientalis), validating the cat as an appropriate felid model. In Study 2, we explored two techniques to enrich cat testis cells for SSCs. We found that the efficiency of enrichment depends on age of the donor and that prepubertal testes are the preferred source for differential plating. Magnetic-activated cell sorting did not achieve any level of enrichment for cat SSCs, likely due to unsuitability of the antibody. The final study modified the traditional mouse SSC culture system for use in the cat. A clear effect of feeder cell type was demonstrated, with mouse endothelial C166 cells supporting a significantly higher number of germ cell colonies as compared to STO cells or primary cat fetal fibroblasts. Identity of germ cell colonies was confirmed by co-expression of UCHL1, PLZF, and OCT4. During subculture, colonies maintained SSC marker co-expression and displayed alkaline phosphatase activity. At the time of writing, cells had been maintained for 78 days in vitro. Together, these studies provide the groundwork towards application of SSC technology in management of rare and endangered felid populations.Item Genetic consequences of habitat fragmentation and restoration(2012) Lloyd, Michael Warren; Neel, Maile C.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The objective my dissertation was to assess the effects of habitat loss and fragmentation on genetic diversity and landscape connectivity. I focused on Vallisneria americana Michx. (Hydrocharitaceae), a submersed aquatic plant species found in the Chesapeake Bay. Vallisneria americana has undergone dramatic changes in abundance and distribution throughout its range and has been targeted for restoration, which makes it ideal for examining the effects habitat loss and fragmentation. I examined the naturally occurring genetic diversity across the Chesapeake Bay and its major tributaries. Sites were genetically diverse, but had a range of genotypic diversities. There were four genetic regions, corresponding with geographic regions in the Bay. Vallisneria americana has been the target of restoration, and restoration techniques could be influencing genetic diversity and potentially lowering overall success. I examined various restoration techniques across eight restoration sites, and found that technique did not greatly influence genetic diversity. However, small population size, significant inbreeding coefficients, and low overlap of allele composition among sites provide cause for concern. Measures of functional and potential connectivity provide insights into the degree of contemporary gene flow occurring across a landscape. Pollen dispersal distance was measured using indirect paternity analysis, and is spatially restricted to only a few meters. Dispersal at this scale imposes small genetic neighborhoods within sites, evidenced by high seed relatedness within mothers. I used a graph theoretic approach to examine the distribution and potential connectivity of historic and current patches of V. americana. There was a high turnover in the distribution of patches, and connectivity varied through time, but even if all habitat were occupied, increases in overall network connectivity would not necessarily be observed. I developed an individual based model that I used to test the ability of measures of genetic differentiation to detect changes in landscape connectivity. Genetic differentiation measures became significant after two generations, but the magnitude of change in each was small in all cases and extremely small when population sizes are greater than 100 individuals. These results suggest that genetic differentiation measures alone are inadequate to rapidly detect changes in connectivity.