Graduate Degree Program in Ecology

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https://hdl.handle.net/10217/100395

These digital collections include theses, dissertations, faculty publications, photographs, and datasets from the Graduate Degree Program in Ecology.

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Open Access
250 years of climate-mediated ecological change in Santa Fe Lake, NM
(Colorado State University. Libraries, 2022) Shampain, Anna, author; Baron, Jill, advisor; Leavitt, Peter, committee member; von Fischer, Joe, committee member; Sibold, Jason, committee member
Mountain lakes are sensitive indicators of anthropogenically driven global change. Lake sediment records in the western United States have documented increased percent carbon and nitrogen and heightened primary productivity indicative of eutrophication in mountain lakes. Recent paleolimnological studies suggest atmospheric nutrient deposition and warming underlie these changes. We analyzed a short sediment core from Santa Fe Lake, NM, the southernmost subalpine lake in the Rocky Mountain Range to investigate patterns in lake biogeochemical and algal biomarkers since 1747. Lake sediments were dated using 210Pb activities and analyzed for percent C and N, δ13C, δ15N, and algal pigments representative of total biomass, chlorophytes, cryptophytes, diatoms, and other primary producers from Santa Fe Lake. Throughout the 250-year sediment record from Santa Fe Lake, we observed changes in algal community composition alongside biogeochemical alterations. During the cold dry conditions of the Little Ice Age, there were greater proportions of cyanobacteria, diatoms, and sulfur bacteria. Total algal biomass increased under increased warming and climate variability with significant increases in chlorophytes and cryptophytes. Significant rates of change occurred concurrently with increases in regional N deposition in the mid-20th century. C, N, δ13C, δ15N remained relatively stable throughout the record, until the mid-20th century when C and N increased exponentially alongside depletions in δ13C, δ15N. Our results suggest climate-driven algal assemblage changes throughout the record with regional N deposition contributing to contemporary productivity increases. The timing and magnitude of these changes differ from other studied lakes. Our findings highlight the heterogeneity of lakes' responses to changing environmental conditions in the Anthropocene and call attention to the role of climate-induced ecological change in the absence of critical N deposition.
Embargo
A case for context in quantitative ecology: statistical techniques to increase efficiency, accuracy, and equity in biodiversity research
(Colorado State University. Libraries, 2024) McCaslin, Hanna M., author; Bombaci, Sara, advisor; Hooten, Mevin, committee member; Koons, David, committee member; Hoeting, Jennifer, committee member
The current era of ecological research is characterized by rapid technological innovation, large datasets, and numerous computational and quantitative techniques. Together, big data and advanced computing are expanding our understanding of natural systems, allowing us to capture more complexity in our models, and helping us find solutions for salient challenges facing modern ecology and conservation, including climate change and biodiversity loss. However, large datasets are often characterized by noise, complex observational processes, and other challenges that can impede our ability to apply these data to address ecological research gaps. In each chapter of this dissertation, I seek to address a data problem inherent to the 'big data' that characterizes modern ecological research. Together, they extend the strategies available for addressing a problem facing many ecologists – how to make use of the large volumes of data we are collecting given (1) current computational limitations and (2) specific sampling biases that characterize various methods for data collection. In the first chapter, I present a recursive Bayesian computing (RB) method that can be used to fit Bayesian hierarchical models in sequential MCMC stages to ease computation and streamline hierarchical inference. I also demonstrate the application of transformation-assisted RB (TARB) to a hierarchical animal movement model to create unsupervised MCMC algorithms and obtain inference about individual- and population-level migratory characteristics. This recursive procedure reduced computation time for fitting our hierarchical movement model by half compared to fitting the model with a single MCMC algorithm. Transformation-assisted RB is a relatively accessible method for reducing the computational demands of fitting complex ecological statistical models, like those for animal movement, multi-species systems, or large spatial and temporal scales. Biodiversity monitoring projects that rely on collaborative, crowdsourced data collection are characterized by huge volumes of data that represent a major facet of 'big data ecology,' and quantitative methods designed to use these data for ecological research and conservation represent a leading edge of contemporary quantitative ecology. However, because participants select where to observe biodiversity, crowdsourced data are often influenced by sampling bias, including being biased toward affluent, white neighborhoods in urban areas. Despite the growing evidence of social sampling bias, research has yet to explore how socially driven sampling bias impacts inference and prediction informed by crowdsourced data, or if existing data pre-processing or analytical methods can effectively mitigate this bias. Thus, in Chapters 2 and 3, I explored social sampling bias in data from the crowdsourced avian biodiversity platform eBird. In Chapter 2, I studied patterns of social sampling bias in the locations of eBird "hotspots" to determine whether hotspots in Fresno, California, U.S.A. are more biased by social factors than the locations of Fresno eBird observations overall. My findings support previous work showing that eBird locations are biased by demographics. Further, I found that demographic bias is most pronounced in the locations of hotspots specifically, with hotspots being more likely to occur in areas with higher proportions of non-Hispanic white residents than eBird locations overall. This relationship is reinforced because hotspots in these predominantly white areas also amass more eBird checklists overall than hotspots in areas with more demographic diversity. These findings raise concerns that the eBird hotspot system may be exacerbating spatial bias in sampling and reinforcing patterns of inequity in data availability and eBird participation, by leading to datasets and user-facing maps of birding hotspots that mostly represent predominantly white neighborhoods. Then, in Chapter 3, I investigated the impacts of not accounting for socially biased sampling when using eBird data to study patterns of urban biodiversity. The luxury effect has emerged as a prominent hypothesis in urban ecology, describing a pattern of higher biodiversity associated with greater socioeconomic status observed in many cities. Using eBird data from 2015-2019, I tested whether an avian luxury effect is observed in Raleigh-Durham, North Carolina, U.S.A. before and after accounting for social sampling bias. By jointly modeling sampling intensity and species richness, I found that sampling intensity and species richness are positively correlated and sampling bias influences the estimated relationship between species richness and income. Thus, failing to account for sampling bias can hinder our ability to accurately observe social-ecological dynamics. Additionally, I found that randomly spatially subsampling eBird data prior to analysis, as recommended by existing guidelines to mitigate sampling bias in eBird data, does not reduce biased sampling related to demographics, because there are data gaps in communities of color and low-income communities that cannot be addressed via spatial subsampling. Therefore, it is paramount that crowdsourced and contributory science projects prioritize more equitable participation in their platforms, both for more ethical, equitable practice and because current sampling inequity negatively impacts data quality and project goals. Quantitative techniques can help us understand the complex observational processes influencing ecological data, and each chapter of this dissertation highlights how tailoring statistical or computing methods to these observational contexts can advance ecological knowledge – either by extending the complexity of models we can feasibly fit, as in Chapter 1, or by acknowledging and accounting for sampling inequity, in Chapters 2 and 3. We are all participants actively shaping the ecological processes we observe, and the actions, approaches, and assumptions used in our research reflect societal systems and biases. Data are never objective, and it is dangerous and false to assume that quantitative techniques can take data out of the contexts in which they were collected. Instead, quantitative frameworks that embrace, reflect, and seek to improve the ways in which social and observational contexts inform what is observed can elevate analytical techniques to tools towards more just, inclusive, and transparent ecological research and conservation.
Embargo
A holistic evaluation of human-elephant interactions in multi-use landscapes
(Colorado State University. Libraries, 2023) Carroll, Sarah Louise, author; Reid, Robin, advisor; Boone, Randy, committee member; Salerno, Jon, committee member; Wittemyer, George, committee member
In East Africa, rangelands and savannas are complex social-ecological systems with a history of land sharing among pastoralists, their livestock and wildlife. Today, many are systems of global importance for biodiversity conservation. As in Earth's other biomes, East African rangelands and their inhabitants face growing challenges as the result of global change, namely ecological, climate, political, and socioeconomic changes that are threatening wildlife populations and straining human-wildlife relationships. African savanna elephants (Loxodonta africana) are key actors in these systems and the center of many of these challenges. Thus, sophisticated land-use planning that addresses the resource use and needs of both people and elephants that can be integrated into conservation policy at relevant scales of governance is a key need for elephant conservation. However, studies of African elephant spatial ecology rarely examine both ecological and human-elephant relationships in the ecosystems they inhabit, whereas existing studies from human dimensions disciplines, which focus on social aspects of human-elephant relationships, very rarely include landscape-specific analyses. Additionally, detailed, spatially explicit information describing human-elephant interactions is limited, particularly in regions where people interacting with elephants still herd livestock more than they grow crops. This dissertation addresses this research need by applying novel methods with a holistic approach to examine the spatial dynamics of human-elephant interactions in multi-use landscapes with a focus on elephant interactions with pastoral peoples and their livestock. Most research in this dissertation is specifically focused on the spatial ecology of human-elephant interactions in the Greater Mara Ecosystem of southwest Kenya and combines inference from images captured by remote camera traps, high-resolution GPS tracking data, and social survey data to: 1) Understand how livestock and land management influence spatiotemporal patterns of elephant occurrence, 2) Investigate elephant movement behaviors and understand how people and environmental variation influence elephant movement behaviors, 3) Map core elephant habitat and movement corridors to support conservation planning, 4) Understand how people in mixed-use savannas relate to elephants and how elephants and wildlife conservation impact their lived experiences, and 5) Map and quantify social willingness to coexist with elephants in mixed-use landscapes to support conservation planning that accounts for the needs of both people and elephants. I found that elephants shifted the quantity and timing of their activity in community conservancies where livestock are present relative to the neighboring protected area where livestock were absent. Elephants were also more likely to occur in the protected area than community conservancies even when controlling for habitat variation. Finally, I found that areas in community conservancies used with higher intensity by sheep and goats, and separately cattle, were somewhat less likely to be used by elephants during the daytime. However, this finding was not consistent across years and the estimated effects had low precision and additional alternative analyses may make this relationship clearer. I then apply network theory to analyze combined information on movement path properties, use intensity, and structural properties of movement networks calculated from GPS tracking data to delineate the functional landscape of movement for elephants in the wider Mara-Serengeti ecosystem. After identifying movement behaviors, I then investigate the environmental variables driving different movement behaviors with a focus on delineating the habitats that support high elephant use and elephant movement corridors. Finally, I contrast how movement behaviors and the environmental variables driving movement vary between elephants inhabiting the mesic, wet savannas of the wider Mara-Serengeti ecosystem with those previously published and observed in elephants inhabiting the xeric savannas of the Samburu-Laikipia ecosystem. Results showed that human presence strongly influenced elephant movement behavior in the Mara and specifically influenced the location of core areas, whereas in Samburu, water availability and vegetation productivity and predictability strongly were the most important variables explaining core area use for elephants. Although vegetation productivity also influenced elephant core area use in the Mara, predictability did not, and human presence and canopy cover strongly influenced core area use in the Mara more strongly than water availability. Overall, these findings indicate that elephants in the Mara are likely less constrained by water and forage availability than elephants in Samburu and have more flexibility to access these key resources while minimizing the risks posed by people. I apply cognitive hierarchy theory to understand how elephants impact people in the Greater Mara Ecosystem by investigating values and attitudes associated with African elephants and elephant conservation in communities sharing space with elephants. I use data collected from semi- structured interviewers at 177 households across a mixed-use, agropastoral landscape that also functions as an unprotected elephant corridor and analyzed responses using Bayesian hierarchical models to quantify positive attitudes towards elephants while accounting for self-reporting bias. I interpret quantitative model estimates in the context of qualitative attitude assessments and sociocultural values to gain a deeper understanding of what explains attitudes towards elephants in the region. We found that although a majority of people expressed positive attitudes about elephant conservation in general, most were not also positive about sharing space with elephants on community and private lands at a local scale. Model estimates showed that people who believed that elephants had sociocultural value were the most likely to be positive towards elephant conservation in general, but experiencing conflict with any wildlife lowered the probability of respondents to have a positive attitude towards sharing space with elephants at a local scale. Qualitative data revealed that safety and well-being concerns related to the perceived threats that elephants pose to human life, livestock, and crops, coupled with few social and economic incentives to support elephant conservation in community and private lands contribute to low local positive attitudes. Our results suggest that conservation approaches focused on sustaining existing sociocultural values and relationships with wildlife while also investing in human well-being and safety measures and could improve conservation outcomes in shared landscapes. Overall, this research develops contributions to the understanding of human-elephant interactions in East African savannas and provides practical applications for elephant conservation. Specifically, this dissertation through the creation of several map products can support conservation planning that accounts for both people and elephants in the Greater Mara Ecosystem. Some of the most important takeaways come from co-interpretation of results with agropastoral communities and can thus provide direct guidance to conservation practitioners on how to better address human well-being in community-based conservation efforts. Though this research was produced in collaboration with non-government organizations, community-based conservation leaders, and government wildlife officials in Kenya, I recommend that future work can improve the collaborative research process by more successfully including local communities as stakeholders at all stages of the collaborative research process.
Open Access
A modeling-experimental (ModEx) approach to advance understanding of global controls and microbial contributions to particulate and mineral-associated organic matter storage
(Colorado State University. Libraries, 2024) Hansen, Paige M., author; Cotrufo, M. Francesca, advisor; Schipanski, Meagan, committee member; Wallenstein, Matt, committee member; Trivedi, Pankaj, committee member
As soils are the largest terrestrial pool of carbon (C) and provision many ecosystem services, including nutrient cycling and maintenance of plant productivity, soil C sequestration represents a promising technology to help meet urgent needs to draw down atmospheric carbon dioxide (CO2) and prevent acceleration of climate change, as well as to help feed a rapidly growing global population. Given this, a comprehensive understanding of the mechanisms underpinning observed patterns of soil C storage is necessary to ensure a sustainable future for all. In response to this need, recent breakthroughs in our understanding of soil organic matter (SOM) dynamics have led to the development of multiple frameworks articulating how climate, soil, plant, and microbial properties interact with one another to control the formation of the two SOM constituents, particulate (POM) and mineral-associated organic matter (MAOM). Despite this, environmental controls that act on POM and MAOM storage at the global scale, as well as microbial functionality, is noticeably absent from our empirical understanding of SOM fraction formation and persistence. More advanced knowledge of these controls would enable more robust identification of where SOM is most vulnerable to loss, as well as more informed implementation of 'multi-pool' management practices aimed at enhancing C storage in both POM and MAOM. In this vein, this dissertation explores global controls on and microbial mediation of SOM dynamics at multiple scales through a combination of synthesis, modeling, and experimental (i.e., ModEx) approaches. Specifically, I first synthesized climate, soil property, and fraction C data to understand global controls on C storage in POM and MAOM. I then applied a previously developed individual-based model (Kaiser et al., 2015) to determine how emergent microbial community properties resulting from microbial social dynamics (i.e., interactions among microbes that produce enzymes at different rates) impact POM retention under varying degrees of MAOM saturation. Lastly, I investigated the relevance of hypothesized microbial copiotrophic and oligotrophic life history strategies to changes in POM and MAOM storage. Results from these projects indicate that global POM and MAOM storage is controlled by disparate suites of environmental variables, with POM being primarily controlled by variables that modulate microbial activity, and MAOM being controlled by a combination of C inputs and soil properties related to the potential to stabilize new MAOM. Additionally, flexible enzyme production in response to the availability of easily-assimilable, soluble substrates may contribute to POM retention under varying degrees of MAOM saturation and POM carbon:nitrogen ratio (C:N). However, variation in microbial function does not always result in changes in POM and MAOM storage – differences in growth rate, our proxy for copio- and oligotrophy, was unrelated to changes in POM and MAOM. Despite this, this dissertation indicates that microbial functions and environmental properties controlling microbial activity rates (i.e., controls on C outputs from the soil) mediate POM storage, but that MAOM is more reflective of C inputs to the soil. This indicates that microbial interventions to support soil C storage may want to focus on ecosystem-specific microbial manipulations that support community efficiency and modulate exo-enzyme production. In combination with other management strategies that increase soil C, these types of microbial interventions may help ensure that new soil C is retained in the soil for longer periods of time. Additionally, given that microbial activity is generally expected to increase with climate warming, these results indicate a premium need to preserve existing POM stocks.
Open Access
A multi-scale analysis of vegetation and irrigation heterogeneity effects on ecohydrological function and ecosystem services in a semi-arid urban area
(Colorado State University. Libraries, 2014) Gage, Edward A., author; Cooper, David, advisor; Ham, Jay, committee member; Kampf, Stephanie, committee member; Ryan, Michael, committee member
To view the abstract, please see the full text of the document.
Open Access
A multi-scale, hierarchical approach to map the location and condition of riparian zones in the southern Rockies ecoregion
(Colorado State University. Libraries, 2014) Salo, Jessica Ann, author; Theobald, David, advisor; Bledsoe, Brian, committee member; Brown, Thomas, committee member; Kampf, Stephanie, committee member; Merritt, David, committee member
Riparian zones are important for their contribution to biodiversity and ecosystem services, especially in the western United States where riparian zones occupy a small proportion of the landscape but support a majority of the biodiversity. Riparian zones are currently threatened by multiple stressors, and will likely face further stresses associated with climate change and additional water withdrawals due to population growth particularly in the western United States and other arid regions. Consequently, it is imperative to understand the current location and extent of riparian zones. Although many agencies and organizations are concerned with the location, condition, and benefits of these ecosystems, few accurate datasets of riparian zone are available over broad spatial extents, and cost-effective methods to map riparian zones at fine spatial resolutions do not currently exist. My dissertation research develops a more comprehensive understanding of the location and condition riparian ecosystems in a semi-arid, mountainous region by developing methods that can be applied to other geographic regions. To do this, I took a three pronged approach to mapping riparian zone location and condition. First, I identify and evaluate existing GIS-based methods that have been previously used to map riparian zones in order to determine how accurately the methods are in a semi-arid, mountainous watershed. Second, I create a multi-scale, hierarchal method to map riparian zones by capturing the dominant physical processes to map the location of current and potential riparian zones using readily available, national datasets and demonstrate the approach for the Southern Rockies Ecoregion. Third, I estimate riparian condition using a straightforward, cost-effective approach at management relevant scales (i.e. reach) and evaluate the dominant ecological and physical processes and anthropogenic stressors that impact riparian ecosystems. Results from my dissertation indicate that existing methods to map potential riparian zones are not very accurate, having only a maximum accuracy of kappa coefficient of 0.38. The most appropriate existing method for mapping potential riparian zones in semi-arid mountainous regions incorporates upstream drainage area and valley topography. I develop a multi-scale, hierarchical, process guided model to map riparian zones and found that the Southern Rockies Ecoregion is composed of 3.2% (± 0.3%) potential and 2.5 (± 0.3%) current riparian zones, indicating that 20.3% (± 1.1%) of riparian zones have been removed by human activities. Based on field verification/validation, my new method has an overall accuracy of 92% for potential riparian zones and 91% in the current riparian zones. Finally, the method I developed to predict riparian condition indicated that riparian zones in the Southern Rockies Ecoregion are comprised of 7.2% low condition, 15.2% medium condition, and 77.7% high condition and that the most important variables in predicting riparian condition in the Southern Rockies Ecoregion are human modification in riparian zones, the number of upstream transportation crossings, human modification within the upstream watershed, and the proportion of the upstream watershed that is protected by GAP Status 1 management plans. The overall accuracy of my riparian condition model was 60.5%. The model could be improved though the use of higher resolution predictor variables. If fine grain (< 5 m) terrain data were available for the study area, additional geomorphic variables, such as valley width to channel width ratio, could be developed and should enhance model performance.
Open Access
A noninvasive method using auditory predator calls and hair snares to detect and genetically sample cougars (Puma concolor)
(Colorado State University. Libraries, 2016) Yeager, Kirstie L., author; Kendall, William L., advisor; Alldredge, Mathew W., committee member; Crooks, Kevin R., committee member; Funk, W. Chris, committee member
A noninvasive method that will sample all individuals in a population over multiple occasions is a useful tool in assessing population demographics with little disturbance to the target animals; however, finding such a method for large carnivores, such as cougars, is challenging due to their elusive nature and large home-range sizes. Current methods to sample cougars usually involve a physical capture component, but obtaining reliable estimates can be difficult and cost prohibitive when using capture as the sole sampling method. Because cougars leave sign, and exhibit behaviors like territoriality and curiosity, a noninvasive-genetic-sampling (NGS) method may be a plausible alternative. Hair contains DNA, which can be genetically analyzed to yield the individual identification necessary for population assessments and can be obtained without handling the animal. I tested NGS techniques using attractants, specifically scent lures and auditory calls, and hair snares to sample cougars at lure sites on the Front Range, Colorado during February – April, 2012 and November, 2012 – April, 2013. First, I established 16 – 20 sites over four ≈ 30-day sampling periods. At sites with auditory calls, photographs documented 40 visits by ≥ 13 individual cougars, and I obtained 14 hair samples. Only two hair samples were collected using scented scratch pads and no samples were acquired via a novel hair snare. Because my initial results indicated calls were more effective attractants than scents, I narrowed my focus to the cubby hair-snare design and increased my effort by establishing 148 lure sites over three or four sampling periods in two study areas: the Front Range (FR; 1,270 km2) and the Uncompahgre Plateau (UP; 540 km2). Each site was active an average of 28.5 days (4,214 sampling nights). On the FR, I observed 98 detections by 13 independent marked cougars, two sibling groups, and ≥ 16 unique unmarked animals. On the UP, I documented 18 detections by seven independent marked cougars. Collectively, 14 of the 20 marked cougars detected were observed multiple times. I used the GPS location data of 27 previously marked cougars to determine availability and estimate detection probabilities. The probability of detecting via camera an independent marked cougar at least once during the study with no assumption of closure (superpopulation) was 0.65 ± 0.11 (FR) and 0.64 ± 0.15 (UP). I collected 59 hair samples. Thirty-two were genotyped at ≥ 8 loci identifying 26 unique cougars. I conclude that auditory calls and hair snares may be an effective way to collect the various biological data that are needed to inform management decisions.
Open Access
A social-ecological approach to managing agricultural ammonia emissions and nitrogen deposition in Rocky Mountain National Park
(Colorado State University. Libraries, 2017) Piña, Aaron Joshua, author; Denning, A. Scott, advisor; Ojima, Dennis S., advisor; Schumacher, Russ S., committee member; Baron, Jill S., committee member; Ham, Jay M., committee member
Atmospheric nitrogen (N) deposition is harmful to nutrient-limited mountain ecosystems. Annual wet deposition of total inorganic N in Rocky Mountain National Park (RMNP) is dominated by ammonium, which primarily comes from agricultural sources. The most wet N deposition events between 1980 and 2015 occurred during summer months. The confluence of summertime mountain meteorology and the location of pollution sources are a perfect combination that leads to high values of wet N deposition in RMNP. In Chapter 2, we tested the importance of convection as a N transport mechanism in addition to large-scale east winds, typically associated with the summertime mountain-valley circulation on the eastern plains of Colorado. We characterized the meteorological transport by using the Weather Research and Forecasting model at 4/3-km horizontal resolution. We used passive tracers as a simplified representation of emissions from a single agricultural source in eastern Colorado during three summer precipitation events where wet N deposition values in RMNP were among the highest recorded in all summers between 1980 and 2015. In all three cases, anticyclones in north-central United States and monsoonal flow associated with the North American Monsoon brought together the necessary conditions for deep convection over RMNP. Output from our simulations suggested large-scale winds were responsible for slow and steady transport whereas convection was a rapid and intermittent form of transport. This chapter showed two scales of transport had an additive effect that led to high deposition of N in RMNP during the afternoon/evening hours of three case studies. Chapter 3 discusses the development of a pilot early warning system (PEWS) for agricultural operators to voluntarily and temporarily minimize emissions of NH3 during periods of upslope winds. The PEWS was created using trajectory analyses driven by outputs from an ensemble of numerical weather forecasts together with the climatological expertise of human forecasters. In this study, we discuss the methods for the PEWS and offer a preliminary analyses of 21 months of the PEWS based on deposition data from two sites in RMNP as wells as voluntary responses from agriculture managers and producers after warnings were issued. Results from this study showed that the PEWS accurately predicted 5 of 7 high N deposition weeks at the lower-elevation observation site, but only 3 of 8 high N deposition weeks at the higher-elevation observation site. With the higher-elevation site receiving pollution from sources both west and east of the Continental Divide, sources west of the Continental Divide would need to be included in the PEWS to capture all of the sources leading to deposition at the higher-elevation site. Sixty agricultural producers and managers from 39 of Colorado's agricultural operations volunteered for the PEWS, and a two-way line of communication between the producers and the scientists was formed. An average of 21 voluntary responses (s.d. 4.9) per warning occurred, with over 75% of the PEWS participants altering their practices after an alert. Solving a broad and complex social-ecological problem requires both a technological approach, such as the PEWS, and collaboration and trust from all participants, including agricultural producers, university researchers, and environmental agencies. Chapter 4 applies a systems approach that explores the actors involved in a complex social-ecological problem that deals with the competing interests of an unadulterated environment and the contribution towards feeding the global population. Agricultural operations in northeastern Colorado are among the densest in the world. The demand of a growing global population has put pressure on the agricultural community to provide large quantities of food in a short amount of time. The cost for higher yields means more water, nutrients, and energy, and the result is environmental degradation in the forms of atmospheric and water pollution. The problem becomes more complex when we mix bottom-up and top-down management approaches. That is, agricultural producers are asked to work together with state and federal agencies on reducing emissions from their operations. A pilot early warning system employed in Colorado since 2014 helped bring together the actors to work towards the common goal of reducing nitrogen deposition in Rocky Mountain National Park. Our goal in this chapter was to organize the problem using a conceptual, social-ecological framework. The case studies and pilot early warning system from Chapters 1 and 2 document starting points for how institutional decisions can incorporate agricultural stakeholders in a mix of bottom-up and top-down management approaches under current and future climatic conditions.
Open Access
A socio-cultural assessment of ecosystem services for community planning and sustainability
(Colorado State University. Libraries, 2018) Beck, Scott Michael, author; McHale, Melissa R., advisor; Jones, Kelly, committee member; Cross, Jeni, committee member; Falkowski, Michael, committee member
Ecosystem service (ES) mapping is a useful mechanism for measuring and communicating ES values spatially; however, most ES mapping is conducted at coarse resolutions over large spatial scales, which calls into question their practicality for local decision-making. Since policy is implemented and managed locally, mapping efforts in Europe, Australia, and the United States have shifted towards local-scale, stakeholder-driven assessments over the past several years. Despite this shift, it is unclear whether similar efforts have been undertaken in Africa, where resource management has direct impacts on impoverished, marginalized communities. The following three chapters in this dissertation represent a novel effort to assess socio-cultural ES in rural South Africa. (Chapter 1) In the first chapter, we conduct a systematic literature review of ES mapping in Africa to identify gaps and trends in research. The intent of this analysis is to: (1) identify where ES maps exist and where coverage gaps remain in ES mapping across the continent; (2) pinpoint which mapping approaches have been used to map ES in Africa and understand whether valuation methods are being integrated in maps; (3) determine whether or not trends in ES mapping in Africa follow recommendations for more localized and inclusive approaches (e.g. socio-cultural & participatory); and (4) assess the appropriateness of management recommendations stemming from these mapping analyses with support from the literature. We identified 25 ES mapping studies, most of which occur in East and South Africa. Additionally, large-scale biophysical approaches are overwhelmingly represented. The results of this review demonstrate that ES mapping research in Africa has not shifted towards local-scale, participatory approaches and that few maps represent local values for ES. Furthermore, 72% of these studies make recommendations for ES management, despite the potential scalar misalignments and lack of community participation in the mapping and valuation of ES. New local-scale ES mapping evaluations are needed to revise our understanding of the potential impacts of decision-making on vulnerable communities. (Chapter 2) In the second chapter, we implement a socio-cultural valuation approach intended to understand how services are valued by people living in rural-urban landscapes. Specifically, we ask: (1) what ecosystem services do communities value; (2) where are these services located on the landscape (parcels vs. communal lands); (3) how do these services relate to land cover; and (4) what are the social and spatial characteristics of households that determine values/demand for services? We implement our study in Bushbuckridge, South Africa using 26 walking interviews and 105 household surveys. We find that communities value an assortment of ecosystem services on both parcels and in communal lands, and roughly 80% of all ecosystem services are associated with tree cover; however, parcels provide a more diverse and sustainable array of services to individuals than communal lands. Additionally, ecosystem service values are at least partially related to how isolated communities are from more urbanized townships. This narrative is counter to previous studies and management plans that emphasize the value of communal lands at the expense of more developed areas. Furthermore, these types of participatory socio-cultural valuations are potentially more representative of community needs, making policy and management strategies based on their results more likely to succeed (or be less harmful). (Chapter 3) In the third and final chapter, our goal is to utilize stakeholder input to map community-identified, socio-cultural ES related to tree cover in urbanizing South Africa at a high spatial resolution. Our specific objectives are to: (1) quantify the probabilities that trees will be used to secure ES benefits both within villages and in communal lands; and (2) map and assess these probabilities to compare villages sampled along a gradient of urbanization. We ask whether or not differences in tree ES values among villages can be captured with high-resolution, local-scale mapping? To achieve these objectives, we link information collected from walking-interviews and social surveys to a high-spatial resolution (1m2) land-cover classification in two rural villages in the Bushbuckridge Local Municipality, South Africa. We apply an advanced HUFF model to calculate and map tree ES use probabilities among these communities within parcels and communal lands. We then compare these probability distributions using violin and boxplots to determine whether or not differences in ES use/benefits among these communities are adequately captured. We find that there are subtle differences among tree ES use probabilities in communal lands among these communities, and more substantial differences among use of ES on parcels, which are determined by community specific ES priorities. These results have important implications for community planning in this and similar regions throughout sub-Saharan Africa.
Open Access
A tail of two fish: an integrative approach to understand how trade-offs and salinity influence two closely related euryhaline fish
(Colorado State University. Libraries, 2021) Mauro, Alexander Anthony, author; Ghalambor, Cameron K., advisor; Hoke, Kim L., committee member; Funk, W. Chris, committee member; Hufbauer, Ruth A., committee member
It is well understood that adaptive evolution can occur rapidly in nature and that anthropogenic climate change is causing - and will continue to cause - mass extinctions of the planet's biodiversity. These facts represent somewhat of a paradox: rapid adaptation can and does occur in nature, yet many populations are failing to adapt to environmental change. This dissertation lies at the interface of this paradox as it investigates the adaptive process. However, instead of investigating a case of adaptive success, it explores the mechanisms and circumstances underlying a case when evolution appears to be constrained. More specifically, it investigates how a trade-off between salinity tolerance and competitive ability contributes to an evolutionary range limit in Poecilia reticulata. It also investigates how salinity influences genetic variation in a more widespread fish, Poecilia picta.In chapter 1, a conceptual framework of trade-offs as evolutionary constraints that utilizes network/pathway thinking is presented. In chapter 2, it is experimentally shown that P. reticulata experiences a trade-off between salinity tolerance and competition with P. picta, that the trade-off is genetically based, and that it is indeed range limiting. In chapter 3 why this trade-off occurs at the physiological network level is investigated. It is shown that a negative relationship between salinity tolerance and competition arises because salinity exposure in P. reticulata results in the activation of hormonally mediated pathways in the brain associated with ion regulation and a decrease in aggression. Chapter 4 shifts the focus from P. reticulata to P. picta. to investigate how salinity influences the distribution of both neutral and adaptive genetic variation in a species that is found both freshwater and brackish water unlike P. reticulata. It is found that salinity can drive differentiation at putatively adaptive loci despite high levels of population connectivity in populations of P. picta.
Open Access
A transportation corridor runs through it: people, wildlife, and transportation systems in national parks and beyond
(Colorado State University. Libraries, 2012) Hardy, Amanda Ruth, author; Crooks, Kevin, advisor; Angeloni, Lisa, committee member; Newman, Peter, committee member; Teel, Tara, committee member; Theobald, Dave, committee member
To view the abstract, please see the full text of the document.
Open Access
Addressing constraints to restoration of highly disturbed ecosystems affected by cheatgrass invasion and slash pile burning
(Colorado State University. Libraries, 2021) Lawrence, Ryan L., author; Paschke, Mark, advisor; Brown, Cynthia, committee member; Meiman, Paul, committee member
To view the abstract, please see the full text of the document.
Open Access
Advancing understanding of the formation and stability of soil organic matter in a changing environment
(Colorado State University. Libraries, 2015) Lavallee, Jocelyn M., author; Conant, Rich T., advisor; Paul, Eldor A., advisor; Cotrufo, M. Francesca, committee member; Borch, Thomas, committee member; Kelly, Eugene F., committee member
Soil is one of our most precious natural resources. It plays a key role in maintaining soil fertility and water quality, and represents a major reservoir in both the global carbon (C) and nitrogen (N) cycles. Soils contain more C and reactive N than the atmosphere and all vegetation combined, the majority of which is found in soil organic matter (SOM). Despite its considerable significance, little is known about the factors that control the formation of SOM, and its stability in the environment. Key questions pertain to whether environmental changes will increase the production of CO₂ during SOM formation and decomposition, forming a large positive feedback to climate change. Answering those questions required a better understanding of how various mechanisms that confer SOM stability are affected by environmental change. My dissertation research aimed to address some of these key questions, and to advance our overall understanding of SOM formation, SOM stability, and the response of stable SOM to changes in the environment. First, I conducted two soil incubation experiments using isotopically labeled (¹³C and ¹⁵N) plant material, which allowed me to track the incorporation of plant-derived C and N into SOM, and efflux of plant-derived C in CO₂. In one soil incubation, I tested the effects of plant litter quality and on the rate and efficiency of SOM formation (a measure of the amount of SOM formed versus the amount of CO₂ lost in the process) by comparing SOM formation from leaves versus roots. I found that plant litter chemistry (C/N ratio) was a reliable predictor of SOM formation after the initial stage of decomposition, with low C/N ratios resulting in more SOM formation and higher formation efficiencies overall. In the second soil incubation, I tested the effect of warming on the rate and efficiency of SOM formation, as well as the rate of destabilization of stable SOM. I found that warming generally led to lower formation efficiencies, causing greater CO₂ production per unit of SOM formed. Warming also led to higher rates of destabilization of stable SOM throughout the experiment. Next, I aimed to investigate the effect of warming on SOM in the field, using soils from two multi-factor climate change experiments. Results from that study suggested that while warming increased the rate of turnover of SOM in some cases, any resulting losses of SOM were offset by increased inputs of SOM, so that total SOM stocks were unchanged. Last, I investigated the persistence of pyrogenic SOM, which is thermally transformed by fire, in the face of land use change at three agricultural sites across the US. I found that pyrogenic SOM was present in all three soils, and had persisted to a greater extent than other SOM with land use change. Many studies of SOM dynamics do not account for pyrogenic SOM, and the results of my work suggest that this lack of accounting can preclude us from fully understanding the mechanisms behind SOM stability. Overall, my work advances our understanding of stable SOM in terms of how it is formed, and whether it will persist in the face of environmental change. Changes in plant litter quality and temperature may lead to changes fluxes of CO₂ to the atmosphere during SOM formation, and while some SOM (pyrogenic SOM) is highly stable in the environment, other SOM is susceptible to loss with warming and land use change. However, in the case of warming, increased plant inputs may offset increased rates of SOM decomposition.
Open Access
Africa's fuelwood footprint and the biome-level impacts of tree harvest
(Colorado State University. Libraries, 2014) Tredennick, Andrew T., author; Galvin, Kathleen, advisor; Hanan, Niall P., advisor; Coughenour, Michael, committee member; Leisz, Stephen, committee member
To view the abstract, please see the full text of the document.
Open Access
Algal blooms in the alpine: investigating the coupled effects of warming and nutrient deposition on mountain lakes
(Colorado State University. Libraries, 2019) Oleksy, Isabella Anna, author; Baron, Jill S., advisor; Spaulding, Sarah A., committee member; Poff, N. LeRoy, committee member; Covino, Timothy, committee member
While 20th century atmospheric nitrogen (N) deposition has been strongly linked to changes in diatom assemblages in high-elevation lakes, contemporaneous changes in other algae suggest additional causes. Using proxies preserved in lake sediments, we explored the origin and magnitude of changes in an alpine and subalpine lake from the end of the Little Ice Age in the 19th century to ca. 2010. We found dramatic changes in algal community structure. Diatom analyses revealed a pronounced shift from majority benthic to planktonic diatoms ca. 1950, coincident with the rise of atmospheric N deposition. Pigments representing benthic green algae have increased 200-300% since ca. 1950; diatom pigments suggest stable or slightly declining populations. Cyanophytes and cryptophytes are not abundant in the sediment record, but there has been a slight increase in some taxa since ca. 1950. While some changes began ca. 1900, the shifts in nearly all indicators of change accelerate ca. 1950 commensurate with many human-caused changes to the Earth system. In addition to N deposition, there have been marked recent increases in aeolian deposition to western mountains that contributes phosphorus. Strong increases in summer air (0.7 °C per decade) and surface water (0.2-0.5°C per decade) temperatures since 1983 have direct and indirect consequences for high elevation ecosystems. While our links between the causes of changes and the responses of mountain lake primary producers are inferred, the drivers and their responses are indicators of changes in the Earth system that have been used to define the Anthropocene. Algal communities (or assemblages) in historically unproductive mountain lakes are shifting, and these changes are taking place commensurate with increasing water temperatures and nutrient availability. However, the mechanisms promoting chlorophytes over bacillariophytes and the implications for ecosystem function are not well understood. We tested the effect of nutrient enrichment on the relative abundance of algal taxonomic groups in a field experiment. We also tested the interactive effects of nutrients and temperature on ecological function of chlorophyte-dominated benthic communities in a laboratory experiment. Nutrient enrichment of both nitrogen and phosphorus favored chlorophytes and led to the highest overall algal biomass. In the absence of nutrient enrichment, the relative abundance of bacillariophytes was significantly greater than chlorophytes and cyanobacteria. Nitrogen assimilation increased significantly, but net ecosystem production decreased, with warming temperatures. Collectively, our results show how chronic N deposition, permafrost thaw, P deposition, and a warming climate interact to alter both the structure and function of mountain lake algal communities. Climate change is altering biogeochemical, metabolic, and ecological functions in lakes across the globe. Historically, high-elevation lakes in temperate regions have been unproductive due to brief ice-free seasons, a snowmelt-driven hydrograph, cold temperatures, and steep topography with low vegetation and soil cover. Observed increases in high elevation lake productivity in the Southern Rocky Mountains over the past decade led us to ask: what are the drivers behind increasing primary productivity? We tested the relative importance of winter and summer weather, watershed characteristics, and water chemistry as drivers of phytoplankton dynamics. Boosted regression tree models were applied using data from 28 high-elevation lakes in Colorado to examine spatial, intra-seasonal, and inter-annual drivers of variability in lake phytoplankton, using chlorophyll a as a proxy. Similar to previous studies, we found that phytoplankton biomass was inversely related to the maximum snow water equivalent (SWE) of the previous winter. However, even in years with average SWE, summer precipitation extremes and warming enhanced phytoplankton biomass. Peak phytoplankton biomass consistently coincided with the warmest water temperatures and lowest nitrogen to phosphorus ratios. While links between declining snowpack, lake temperature, nutrients, and organic matter dynamics are increasingly recognized as critical drivers of change in high elevation lakes, this study identifies additional processes that will influence lake productivity as the climate continues to change. Continued changes in the timing, type, and magnitude of precipitation in combination with other global change drivers (e.g., nutrient deposition) may have consequences for production in high elevation lakes, potentially shifting these historically oligotrophic lakes toward new ecosystem states.
Open Access
Altering water and nitrogen availability after roadside disturbance to favor native plant species
(Colorado State University. Libraries, 2016) Ringer, Lindsay, author; Brown, Cynthia S., advisor; Claassen, Victor P., committee member; Schipanski, Meagan E., committee member
This study evaluates the use of soil amendments in roadside restoration to promote native species and discourage invasive species establishment through manipulation of water and nitrogen (N) availability. Our goal was to decrease soil N availability and increase soil water content to foster growth of perennial native species on roadsides in Rocky Mountain National Park, Colorado. Roadside construction can increase soil bulk density, reduce aggregation, and cause an initial increase in resource availability, which encourages growth of early successional species. In addition, N deposition from the Front Range of Colorado is increasing nitrate and ammonium availability in this National Park. The study objective was to increase or decrease water and/or N availability with soil amendments to reduce weedy annual species establishment on roadsides. Treatments were hypothesized to 1) increase soil moisture and reduce plant-available N (synthetic polymer incorporation), 2) reduce soil surface temperatures, increase moisture and indirectly decrease N (wood mulch blanket), 3) decrease bulk density by changing soil structure and slowly increase N (yard-waste compost incorporation). These amendments were applied alone and in pairwise combinations to six southeast facing roadsides slopes concurrent with seeding in fall of 2013. Ten perennial grass and forb species were hydro-seeded with tackifier to all roadsides. Plant density, cover, mineral nutrients, soil moisture, total C:N, soil temperature, and rainfall were measured during the growing season in 2014 and 2015. A paired greenhouse study was conducted in spring 2014 with analogue native and non-native grasses. Grass root and shoot biomass, plant height, seedling density, and soil moisture were measured after 9 weeks of growth. On these roadsides, soil moisture, and density of native seeded species was significantly changed by soil treatments through time (p=0.039, p=0.040). Wood mulch alone and combined with compost or polymer increased soil moisture after rainfall in the field (p=0.0007) and after irrigation in the greenhouse (p=0.0001). In the field, seeded species density was highest in mulch/compost treatments in 2014 (p=0.029) and mulch/polymer treatments in 2015 (p=0.003). After one year of decomposition, none of the treatments significantly changed carbon to nitrogen ratios (p=0.27) which averaged 18.7:1, although mulch/compost treatment had the lowest C:N ratio of 13.5:1. Mulch or mulch/polymer treatments combined had much less nitrate than yard-waste compost incorporation (p=0.0002). Mulch blanket immobilized N and decreased non-native density in summer 2015 to 2 plants/m2. In contrast, compost/polymer treatments had 12 non-native plants/m2 (p=0.02). In the greenhouse, nitrate was more limiting than water, and mulch blanket increased native grass growth relative to non-native grasses (p=0.002). Because of the immobilization of N, mulch also decreased germination rates (p=0.001) and biomass (p=0.001) across all species. With higher soil moisture availability in the greenhouse, non-native growth was lower than natives in control (p=0.001), polymer and mulch soil treatments. In contrast, compost incorporation, which increased N availability in the field, drastically increased growth of all species (p<0.0001) in the greenhouse. These results begin to demonstrate how increased soil moisture and decreased soil N favors germination and seedling survival of desirable native perennial species, while simultaneously reducing non-native species establishment. By managing soil resource availability after disturbance, we can achieve resilient plant communities dominated by perennial native species.
Open Access
An alternate state approach to range management in the sagebrush steppe
(Colorado State University. Libraries, 2011) Kachergis, Emily, author; Fernandez-Gimenez, Maria Edith, advisor; Rocca, Monique Elisabeth, 1974-, advisor; Hobbs, N. Thompson, committee member; Knapp, Alan K., 1956-, committee member
Describing and predicting sudden shifts between alternate states in ecosystems is a frontier in ecology with important implications for natural resource management and human well-being. The range profession has recently adopted an approach to land management decision-making based on alternate state theory. The Natural Resource Conservation Service and partners are creating state and transition models (STMs), conceptual models that describe shifts in ecosystems, for many types of land throughout the US. Motivated by this national STM-building effort, this dissertation has two practical objectives: 1) to create data-driven STMs that describe sagebrush steppe ecosystem response to management, and 2) to develop guidelines for STM creation. A third objective grew out of the need to create theoretically accurate STMs: to determine whether spatial and temporal patterns of vegetation in northwest Colorado sagebrush steppe are consistent with predictions of alternate state theory. The first chapter introduces this work with a review of alternate state theory and how it is applied in constructing STMs. I conducted an observational study of sagebrush steppe response to management practices and ecological disturbances on two soil types in the lower Elkhead watershed. The second chapter examines plant species composition as an indicator of alternate states, a test of the current approach to building STMs. The third chapter investigates whether areas with different structure also differ in function, as predicted by alternate state theory. The fourth chapter compares trait-based group composition to species composition as an indicator of alternate states. From these chapters, I conclude that there are large, management-relevant differences in species composition within environmentally similar areas and that many of these differences are related to site history, as would be expected if these represent alternate states. The Indicators of Rangeland Health show that some states defined by species composition are associated with unique processes that may serve as positive feedback mechanisms which maintain alternate states. Relationships between species composition, processes and environmental gradients suggest that environmental variation may make some transitions between states more likely and should be acknowledged in STMs. Multiple-trait based group composition identifies many of the same potential states and transitions as species composition, but is also sensitive to some different management practices. The Indicators of Rangeland Health and plant traits are simple additions to current STM-building methods that can improve and expedite STM creation. In the final chapter, I describe long-term sagebrush steppe dynamics based on 50 years of monitoring data from the upper Elkhead watershed and evaluate evidence for alternate states. Gradual changes in composition after spraying and the steady increase of a non-native grass suggest that this high-elevation sagebrush steppe ecosystem does not experience sudden shifts between alternate states. I conclude that the alternate state approach to range management shows promise for describing management-relevant ecosystem dynamics and organizing current knowledge. Given the equivocal evidence supporting predictions of alternate state theory for Elkhead watershed sagebrush steppe, further research should determine which aspects of alternate state theory must be confirmed to create useful STMs. In addition, long-term monitoring, modeling, and experiments are needed to validate and update models as we learn more about the sagebrush steppe.
Open Access
An eco-epidemiological approach to management of tuberculosis in free-ranging and captive wildlife
(Colorado State University. Libraries, 2018) Rosen, Laura Elizabeth, author; Olea-Popelka, Francisco J., advisor; Miller, Michele A., committee member; Huyvaert, Kathryn P., committee member; Hobbs, N. Thompson, committee member
Tuberculosis (TB) is a disease of global importance affecting millions of humans, livestock, and wildlife. Control and eventual eradication of TB depends on dedicated management actions for all species. Accurately diagnosing TB can be challenging in wildlife species, for which validated tests may be unavailable or of limited sensitivity or specificity. Managing TB in wildlife poses additional difficulties, requiring considerable time and resources to implement at an appropriately broad scale. Each unique ecosystem where TB occurs requires management interventions designed to meet the area's conservation, ecological, social, and financial needs. In this dissertation, I explored the diagnosis and management of tuberculosis in wildlife in three different settings: free-ranging European badgers (Meles meles) in Ireland, working African elephants (Loxodonta africana) in Zimbabwe, and captive African and Asian elephants (Elephas maximus) in North America. Badgers are a reservoir of bovine TB in Ireland, while captive elephants around the world are at risk of TB from their human handlers. Badgers have historically been managed by culling, but there is a current transitioning to vaccination as the primary management tool. In contrast, captive elephants in high-resource settings are typically treated for TB upon diagnosis, although this option may be limited in low-income countries. The first objective of this research was to assess the impact of environmental factors in management of TB over three different studies. I explored how biotic and abiotic factors influence trapping success of badgers being managed for bovine TB in Ireland. In a second study of badgers, I estimated density of a population undergoing vaccination in relation to environmental variables and prior management history. Underlying badger density is an important driver in the TB disease dynamics between cattle and badgers, and can be used in predictions about and assessment of outcomes under vaccination. Finally, I examined potential risk factors for TB seropositive status in working African elephants in Zimbabwe, and identified unique potential exposures from the environment. The second objective of this dissertation was to study the performance of diagnostic tests in a novel setting and interpret the results in the context of exposures within the ecosystem. This study employed two serological tests, STAT-PAK and DPP, for the first time in working African elephants in a range country. I interpreted the results suggestive of exposure to mycobacteria in some elephants based on possible interactions with the complex community of humans, livestock, wildlife, and mycobacteria. The third objective of this dissertation was to develop recommendations for TB management programs based on surveys, capture data, and consideration of individual, population, and community factors. The results from our badger trapping study in Ireland formed the basis of suggested conditions under which vaccine delivery can be increased, because captures are most likely. We used mark-recapture data to estimate badger density in a vaccination area, which adds an important dimension to the Irish TB management program that includes badgers and cattle. Population density is an important factor in pathogen transmission and estimating density using these methods may be a priority for other wildlife populations being managed for TB. Our study of TB treatment in elephants provided a compilation of empirical data for elephant managers and veterinarians to inform clinical decision making. It also underscores the need for improved diagnostics to more confidently identify when animals are no longer infectious. For working African elephants, we documented other wildlife species with host potential on and around facilities, and considered these as possible sources for mycobacterial transmission. Our management guidelines for TB prevention specifically include measures to reduce direct and indirect contact with potential host species. Management of TB across humans and animal species remains a challenging prospect. A One Health approach that incorporates data and techniques across disciplines to build a complete picture of disease control is ideal for TB in wildlife. I drew from ecology and epidemiology to implement a holistic approach to diagnosing and managing TB in species of conservation concern, provide insight into the challenges of diagnosing and managing TB in free-ranging and captive wildlife, describe the benefits of a transdisciplinary approach, and expose areas in need of further research.
Open Access
An introduced plant affects the structure and function of riparian food webs
(Colorado State University. Libraries, 2017) Riedl, Hannah, author; Clements, William, advisor; Pejchar, Liba, advisor; Kondratieff, Boris, committee member; Fausch, Kurt, committee member
Aquatic and terrestrial ecosystems are closely linked by the reciprocal flux of resource subsidies, but these dynamics can be uncoupled by anthropogenic change. Introduced species are easily spread by riverine systems, but the effects of non-native riparian vegetation on reciprocal arthropod subsidies are essentially unknown. I studied the aquatic and terrestrial arthropod communities, and their flux into and out of the stream channel, in stream reaches in northwestern Colorado invaded and uninvaded by New Mexico locust (Robinia neomexicana A. Gray), a woody plant north of its native range. I also evaluated whether the aquatic- and terrestrial-derived diets of riparian songbirds were altered in stream reaches with New Mexico locust. I found that reaches with New Mexico locust had fewer terrestrial arthropods collected from vegetation, particularly in spring. Consistent with these results, some songbird species using invaded sites displayed diet shifts towards aquatic-derived resources. Aquatic resources comprised approximately 34% of the songbird assemblage's diet, which highlights the importance of aquatic subsidies to riparian consumers. In contrast, there were no impacts of New Mexico locust on the aquatic insect community associated with the invasion. Overall, seasonal and annual variation best described patterns of arthropod subsidy production and consumption. Since locust invasion did not drive strong patterns in insect communities, and because seasonal and annual factors provide little information about environmental drivers of resource subsidies, we also assessed the importance of vegetation and stream characteristics on aquatic and terrestrial arthropod communities. I found terrestrial insect biomass and richness increased with percent ground cover, forb cover, and vertical vegetation structure, and decreased with percent cover of New Mexico locust. Interestingly, vegetation characteristics best described emergence patterns of adult aquatic insects, but stream characteristics best described larval aquatic insect patterns. Our results support the use of a multi-functional approach to assessing ecosystem alteration. By evaluating the multiple pathways through which a non-native species can affect riparian systems, I found a close connection between stream and riparian ecosystems. I found the impacts of invasion were most apparent for arthropod metrics directly related to vegetation (i.e., arthropods collected from foliage), with weaker responses for indirect metrics (i.e., aquatic insect biomass, songbird diet components).
Open Access
Analysis and modeling of what honey bees (Apis mellifera L.) bring back to the hive and how that affects the health of the hive and humans
(Colorado State University. Libraries, 2023) Awad, Mai Mousa, author; Boone, Randall, advisor; Kato, Takamitsu, advisor; Borch, Thomas, committee member; Ode, Paul, committee member
Apis mellifera L. populations are decreasing at an alarming rate. Over the past 20 years, the number of managed honey bee colonies has declined, and this decline has become a global concern. This study focuses on chemical stressors that are found to affect the bee population. We used direct sampling to examine the variation of pesticides and heavy metals concentrations in two different landscape contexts. Subsequently, we extrapolated the risk of these toxins' residues on Apis sp. based on current literature. We found no spatial variation in metal concentrations in pollen and honey samples collected from urban and agricultural areas. Likewise, we observed no spatial variation in pesticide concentrations in pollen and honey samples collected from urban versus agricultural areas. In addition to chemical factors, we studied the nutritional factor by investigating the effect of spatial variability on the amount of stored pollen and the floral diversity of in-hive pollen. Furthermore, we estimated the most abundant botanical families that will identify honey bees' protein-source preferences. The results indicated a spatial variation in Shannon-Weaver diversity, demonstrating a higher diversity index with a wider variety of pollen taxa collected from urban sites compared to the agricultural ones with a lower diversity index with less pollen taxonomic variety. The alarming decrease in honey bees' population urges researchers to investigate the factors that enhance the deterioration of bees' population. A few models explained these factors individually. We designed a NetLogo model to assess multiple factors that would intensify the impact of the Colony Collapse Disorder phenomenon, by investigating the spatial variation of bees' exposure to a distinctive environmental toxin and the quantities of these toxins in hive products. The model indicated that there were significant spatial variation effects on the pesticides and heavy metal concentrations in the accumulated pollen and nectar inside the beehive. Pesticides and heavy metal accumulation in bees' products are mainly caused by human activities, which can affect human health by their consuming contaminated honey. Based on the results of honey analysis for pesticides and heavy metals we performed in the first study, we decided to select one pesticide and a pesticide synergist along with the most two abundant heavy metals to investigate the synergistic effect of cytotoxicity and genotoxicity that would result from the interaction of one major pesticide in honey: Imidacloprid and a pesticide synergist: Piperonyl butoxide, and two major heavy metals in honey: Lead and Selenium, at the cellular level in mammalian cells, where we found different interactional effects of these compounds on cell survival, cell apoptosis, oxidative stress, and sister chromatid induction.