Browsing by Author "Knapp, Alan, committee member"
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Item Open Access A study of long-term soil moisture dynamics: assessing biologically available water as a function of soil development(Colorado State University. Libraries, 2015) Salley, Shawn William, author; Kelly, Eugene F., advisor; Martin, Patrick H., advisor; Knapp, Alan, committee member; Kahosla, Raj, committee memberForecasting ecosystem responses to global change is highly uncertain in light of the alarming rates of climate change predicted by the scientific community. Rising COâ‚‚ concentrations not only cause increased warming, but may also influence the amount and distribution of rainfall in terrestrial ecosystems. This in turn affects plant growth and the ability of ecosystems to perform important functions including nutrient cycling and decomposition. Soil moisture is considered the major control of ecosystem structure and function, and it is considered the most limiting resource to biological activity in semi-arid grassland ecosystems. Total soil moisture potentials are controlled by edaphic properties such as texture, structure, micro-porosity, bulk density, soil depth, clay mineralogy, and organic matter content. Physical and chemical properties interact with hydrologic inflows and outflows to control soil moisture causing the soil to act as a store and regulator in the water flow system of the overall ecosystem. Thus, the soil acts as both temporary storage of precipitation inputs and as a regulator controlling the partition between inputs and the major outflows: evapotranspiration, runoff, leaching, and flow between organisms. Understanding the pedologic controls of water retention is critical in considering the long-term dynamics of ecosystems and projecting the consequence of global change. The focus of my dissertation is twofold: to elucidate the change in water holding characteristics of soils through pedogenesis and to quantify how global change will impact soil moisture in the U.S. Great Plains. In order to best address my research questions, I began by studying two established soil-chronosequences in northeast Colorado and central Wyoming to assess the characteristics of soil's physical and chemical properties. I examined how they control the biologically available water holding capacities that change predictably as a function of soil age. Next, I examined other notable soil chronosequences across the western United States to test the millennial evolution of soil water holding capacities through various climates and soil parent materials. Finally, I used a soil moisture simulation to spatially model the historical, contemporary, and future projections of soil moisture on the Great Plains. I found in semi-arid ecosystems that three broad stages of soil development exist and are linked to landscape ages that are ecologically and biogeochemically significant: aggrading, equilibrium, and retrogressive stages. Soils in the aggrading stage are typically weakly developed, have genetically simple horizon differentiation, and minimal water retention. Prominent clay and carbonate features are expressed in the equilibrium stage soils which show more complex soil horizonation, structure, aggregation, and porosity. Within these intermediate soils, the capacity to store water reaches a maximum. Declining or retrogressive stage soils show losses of clays and carbonates, have undergone extensive leaching, and the soil's capacity to store water is at a minimum compared to the aggrading and equilibrium stages. Furthermore, I confirmed when modeling soil moisture in the Great Plains that course-textured landscapes store less soil water and when accompanied with disturbance are more vulnerable to climate change. Overall, my dissertation focuses on understanding the role pedogenesis has on soil water holding characteristics and how global change impacts semiarid landscapes. My results have helped improve understanding of long-term ecosystem biophysical feedbacks through quantifying soil moisture retention characteristics across soil age and climatic processes by linking soil water properties to climatic and pedogenic variables.Item Open Access Analyzing root traits to characterize juniper expansion into rangelands(Colorado State University. Libraries, 2016) Chesus, Kelly A., author; Ocheltree, Troy, advisor; Comas, Louise, committee member; Knapp, Alan, committee memberJuniper expansion into sagebrush communities is a widespread phenomenon occurring across large regions of the western U.S. over the past century. Fire suppression and increased grazing activity are commonly considered as the primary drivers of expansion but they do not explain all instances of expansion. In order to develop a complete explanation for the success of juniper we investigated the competitive abilities of J. osteosperma (Utah juniper) and A. tridentata (big sagebrush) based on fine root traits, including specific root length (SRL), fine root diameter, and fine root biomass, and spatial patterns of water use inferred from stem and soil stable oxygen isotopes (δ18O). Data were collected from three different age classes of J. osteosperma (seedling, sapling, and mature) to better understand the competitive abilities at different life stages. J. osteosperma age classes were originally determined by height and later aged from cross sections. The youngest seedling in our study was 14 years of age, therefore we refer to the seedlings in this study as 'advanced.' Advanced J. osteosperma seedlings demonstrated the ability to switch their reliance from shallow to deep water sources later in the season, potentially enhancing their survival particularly during drought events. A. tridentata had traits associated with faster root proliferation and resource acquisition (significantly greater SRL and smaller root diameter) suggesting competition for limiting resources is likely not a primary driver of expansion of J. osteosperma.Item Open Access Constraints in the compensatory response of a tallgrass prairie plant community to the loss of a dominant species(Colorado State University. Libraries, 2020) Chaves RodrÃguez, Francis Andrea, author; Smith, Melinda, advisor; Knapp, Alan, committee member; Ocheltree, Troy, committee member; Sala, Osvaldo, committee member; Webb, Colleen, committee memberBiodiversity loss is one of the major consequences of global change driven by human activities. The loss of a dominant species is expected to have profound consequences on ecosystem processes (e.g. aboveground productivity) given their highest relative abundance and proportionally large contribution to community biomass production. However, through competitive release, the newly available resources following its lost, are expected to be utilized by the remaining species in the community to increase in abundance and compensate for the function lost. Complete functional compensation does not occur in every ecological community following the loss of dominant species or entire functional groups, and 1) limited resource availability, 2) absence of functionally redundant species, and 3) lack of functional traits that promote compensation have been proposed as possible constraints on compensation. In this dissertation, I evaluate the effect of removing these constraints on the biomass compensation response of a tallgrass prairie plant community following the loss of the dominant species, the C4 tallgrass, Andropogon gerardii Vitman. I experimentally removed the dominant species from a native intact tallgrass prairie plant community at Konza Prairie Biological Station, Kansas, where I selected two contrasting sites, one with functionally redundant species Panicum virgatum L. and Sorghastrum nutans (L.) Nash in low abundances, and a second site where those functionally redundant were codominants with A. gerardii. The first site was irrigated to alleviate water limitation during four growing seasons and fertilized with nitrogen during the final season of the experiment. The second site did not exhibit water limitation and was fertilized during the second growing season of the two-year experiment. My results show that in the short-term removing resource limitation promoted aboveground primary productivity but not enough to produce full biomass compensation. The presence of functionally redundant species, also C4 tall grasses with similar functional effect traits as A. gerardii, did increase aboveground biomass production, but did not promote full biomass compensation, not even when they were present in high abundance. I hypothesize that additional to the constraints proposed, compensation is limited by response traits in the remaining species that limit their demographic response to the increased available space, light, water and soil resources following the loss of the dominant species. Overall, my results show the compensation approach is important to evaluate not only the effect of species loss on ecosystem processes, but also the response of the remaining species and their ability to compensate for the function lost. They also suggest the existence of additional mechanisms in play that need to be identified and tested in order to improve the understanding of how communities recover in the face of biodiversity loss.Item Open Access Defining, describing, and assessing growth determinacy as a mechanism of plant species codominance(Colorado State University. Libraries, 2022) Gray, Jesse Edward, author; Smith, Melinda, advisor; Knapp, Alan, committee member; Ocheltree, Troy, committee member; Blumenthal, Dana, committee memberTo view the abstract, please see the full text of the document.Item Open Access Dynamics of stress and mortality for grass dominated ecosystems: an interplay of water limitation, heat, and erosion(Colorado State University. Libraries, 2024) Bradfield, Scott J., author; Ocheltree, Troy, advisor; Knapp, Alan, committee member; Augustine, David, committee member; Hoffman, Chad, committee memberGrass dominated systems account for ~40% of the earth's terrestrial surface and typically occur in semi-arid and arid regions. The plant species that grow in these systems are known for their ability to withstand disturbance, including drought, grazing, and fire. While it is understood that the plants in these systems often experience multiple forms of stress in a growing season, interactions among these stress variables are not well represented in the literature. In this research, I sought to determine how combinations of stress variables influence the shortgrass steppe, this includes: long-term grazing, drought, erosion, and temperature. Specifically, I examined (1) how the interaction of long-term grazing and drought influences the recovery of the vegetation on the SGS following single-year and multi-year droughts, (2) how the interaction of grazing and erosion influence mortality following exposure to extreme surface temperatures, and (3) performed a comparative analysis of the microclimate of grass dominated systems in the United States to determine the intensity and frequency of stressful abiotic conditions that the vegetation experiences. First, I quantified the interactive effects of single and multi-year droughts with grazing pressure, because the Bouteloua species that dominate the region have been shown to be tolerant of grazing and drought independently, but the interactive effects of the two have not been well studied. Past research has focused on heavy cattle grazing but I included a mixture of moderate cattle grazing with prairie dogs, which is more intensive grazing than heavy cattle grazing. I found that the combined stress of multiple years of drought along with high grazing pressure has the potential to increase mortality in these Bouteloua species. Next, I quantified the erosion severity by ranking the amount crown exposure of the Bouteloua species during a drought on the SGS and then determined how erosion influenced bud outgrowth (production of a tiller) during the recovery year. I combined these data with environmental data collected by the National Ecological Organization Network (NEON) to determine the environmental conditions that the meristems of the plants experienced during the drought. My results showed that the temperatures at the surface of the soil, and exposed meristems, frequently reached levels thought to be lethal to plant cells. I acknowledge that it was likely a combination of water deficit and temperature that led to mortality of Bouteloua species that experienced erosion, but the high temperatures alone had the capacity to cause mortality of the meristems. Finally, I compared several near surface micrometeorological variables of grass dominated systems across the United States. Ultimately, I wanted to determine the frequency that these systems experienced temperatures near the surface that would be damaging to plants, if conventional methods for determining heatwaves represents damaging conditions to grassland plants, and what environmental factors lead to potentially damaging surface temperatures. I found that damaging temperatures occur often at arid sites, conventional heatwaves overestimate heat stress in sites that are wet or at higher latitudes, and underestimates heat stress for arid sites.Item Open Access Ecological and social consequences of collaborative bison reintroduction in the western U.S.(Colorado State University. Libraries, 2018) Wilkins, Katherine DeWitt, author; Pejchar, Liba, advisor; Knapp, Alan, committee member; Garvoille, Rebecca, committee member; Knight, Rick, committee memberCollaborative conservation has been underway for centuries in diverse communities across the globe. More recently, collaborative groups of private and public land managers have coalesced around common natural resource objectives in the United States. This dissertation advances the science and practice of collaborative conservation through a literature review and two highly collaborative projects on bison reintroduction in the western United States. My specific objectives are: 1) To evaluate the status and impact of collaborative conservation groups in the United States; 2) To assess the ecological consequences of bison reintroduction for birds, mammals, and plants in Colorado's shortgrass prairie; 3) To understand how bison reintroduction affects human connections to grassland landscapes; and 4) To compare the effects of bison and cattle grazing on birds and plants in Colorado and New Mexico. To evaluate the status of U.S.-based collaborative conservation groups, I conducted a literature review to identify what factors motivate group formation, and to quantify biophysical, social, and economic goals, actions to achieve those goals and outcomes, and how outcomes were assessed. I also characterized the geographic distribution, participants and funding sources of U.S.-based collaborative conservation groups. To accomplish these objectives, I searched for peer-reviewed journal articles, book chapters, and reports in online databases, resulting in 174 papers that described 257 collaborative conservation groups in all 50 states. Overall, information on outcomes and how groups assessed outcomes was sparse. For those groups with published outcomes, most outcomes had positive results for biophysical, social, and economic goals. To assess the ecological consequences of species reintroduction and how reintroductions may catalyze public engagement in grassland conservation, I assessed both the ecological and social effects of bison reintroduction to northern Colorado. Specifically, I explored the effect of bison reintroduction on: 1) bird density and habitat use, 2) mammal habitat use, 3) vegetation composition and structure, and 4) human connections (place attachment) to a shortgrass prairie. To measure ecological responses, I surveyed birds, mammals, and plants before and after bison reintroduction. To understand how bison shape visitor connections to grasslands, I gave structured surveys to people who visited the site before and after bison reintroduction. I found few short-term effects of bison on grassland birds, mammals, and plants. However, I measured a significant increase in place attachment to the grassland site post reintroduction. These results suggest that bison reintroduction does not have strong, short-term ecological effects, but does have immediate, positive benefits for connecting people to ecosystems. I recommend that future projects prioritize monitoring ecological and social outcomes to advance the science and practice of bison reintroduction. To understand whether non-native species can serve as proxies for extinct or rare native species, I evaluated the role of bison and cattle grazing in shaping habitat for grassland birds and plants. To compare ecological responses, I surveyed birds and plants between bison, cattle, and reference sites in Colorado and New Mexico. While I found few differences in plant height and cover among bison, cattle, and reference sites, I did find significant differences in bird densities among the sites. In both Colorado and New Mexico, some grassland obligate birds preferred bison sites, while others preferred cattle sites. Bison and cattle may serve as reciprocal ecological surrogates in cases where they have similar densities on the landscape, where cattle graze on a rotational system. Overall, my dissertation demonstrates that collaborative conservation often achieves success, but these outcomes are not always assessed or reported. I also show that a highly collaborative bison reintroduction effort in Colorado had few ecological effects in the short-term, but did help connect people to a grassland landscape. In addition, my study found that collaboratively managed bison and cattle herds in Colorado and New Mexico create viable habitat for obligate grassland birds.Item Open Access Moving beyond mass loss: advancing understanding about the fate of decomposing leaf litter and pyrogenic organic matter in the mineral soil(Colorado State University. Libraries, 2014) Soong, Jennifer L., author; Cotrufo, M. Francesca, advisor; Wallenstein, Matthew, committee member; Knapp, Alan, committee member; Parton, William, committee memberLeaf litter decomposition recycles the energy and nutrients fixed by plants during net primary productivity back to the soil and atmosphere from where they came. Traditionally, leaf litter decomposition studies have focused on litter mass loss rates, without consideration for where that mass ends up in the ecosystem. However, during litter decomposition by soil microbes a fraction of the litter mass lost is truly lost to the ecosystem as respired CO2, while another fraction remains in the ecosystem stored in the soil as soil organic matter (SOM). SOM is heterogeneous in composition, with various SOM pools remaining stored in the soil for time spans ranging from days to millennia depending on their biochemical and physical properties. Pyrogenic organic matter (py-OM) is the partially combusted plant residue left behind by fires, and has been found to contribute to long term SOM pools. SOM accounts for the largest terrestrial pool of carbon (C) in the global C cycle and stores nitrogen (N) and other nutrients for plant productivity. Therefore the formation of SOM during litter decomposition is critical to terrestrial C and N cycling and its feedback to global biogeochemical cycles. The focus of my dissertation is the study of leaf litter and py-OM decomposition, and quantitatively tracing how much decomposing litter and py-OM is used by soil microbes, how much is lost as CO2, and how much remains in the soil and contributes to SOM formation under different conditions. In order to best address my research questions, I first studied the methods of leaching of dissolved organic carbon (DOC) and 13C and 15N isotope labeling of plant material in the laboratory. Then, I conducted a laboratory incubation where I found that the amount of hot water extractable C and the lignocellulose index (Lignin/(lignin+cellulose)) can be used to predict DOM leaching, and the partitioning of C loss between DOC and CO2 from leaves and py-OM during decomposition. I also conducted two field studies using 13C and 15N labeled Andropogon gerardii leaf litter and py-OM to trace the fate of C and N losses during their decomposition in a fire affected tallgrass prairie, and understand the role of soil microarthropods in this process. I found that soil microarthropods increase the amount of leaf litter C that contributes to stabilized SOM formation during litter decomposition, by increasing litter inputs to the soil where they can be utilized by soil microbes. Finally, I found that frequent inputs of py-OM, rather than litter, due to annual burning of the tallgrass prairie alters the SOM formation process by removing relatively labile litter inputs to the soil and replacing it with py-OM that is unusable by soil microbes. Overall, my dissertation has focused on taking a mechanistic approach to understanding the process of litter and py-OM decomposition, and how their decomposition contributes to SOM formation and ecosystem CO2 fluxes. My results have helped to improve our understanding of terrestrial biogeochemistry, and the processes that control SOM formation during litter decomposition.Item Open Access Response and recovery of grassland plant communities exposed to multiyear drought differs across a precipitation gradient(Colorado State University. Libraries, 2022) Ross, Maggie, author; Smith, Melinda D., advisor; Knapp, Alan, committee member; Havrilla, Caroline, committee member; Wilkins, Kate, committee memberDrought events are expected to increase in grassland ecosystems in many regions of globe due to climate change. Much is known about the effects of drought on grassland plant communities, yet it is difficult to compare responses across different grassland ecosystems because studies impose drought with varying characteristics. Further, few studies have documented plant community recovery, even though the impacts of drought can persist for multiple years. We experimentally imposed four years of extreme, growing season drought at four sites representing the major Central US grassland types (shortgrass steppe, mixed grass prairie, tall grass prairie) spanning a precipitation gradient. Growing season drought was imposed in two ways: 1) by reducing each rainfall event by 66% (chronic) or 2) by completely excluding rainfall until a similar reduction in precipitation as the chronic treatment was achieved (intense). Plant community responses to the two drought treatments were monitored for each year of the four-year drought treatments and four years following the drought to assess recovery. Overall, plant communities at the drier sites responded sooner to drought and took longer to recovery than the wetter sites. Plant composition was altered at all sites, which was largely driven by shifts in the dominant C3-C4 grasses and subsequent species reordering and to a lesser extent by changes in richness in evenness. There was a significant decrease in C4 graminoid abundance in response to drought at all sites with a corresponding increase of C3 annual grasses during the drought at the mixed grass sites but not until the recovery period at the shortgrass steppe. Cheatgrass (Bromus tectorum) invaded the shortgrass steppe during the drought and proliferated during the recovery period, which likely pushed the communities into an alternate state, and inhibited recovery after four years of ambient conditions. The northern mixed grass prairie also did not fully recovery after four years, which indicates that full plant community recovery can extend longer than the drought itself at these drier sites. While there is some indication that intense drought had a greater impact on communities than chronic drought, there is limited evidence to suggest that drought type significantly influenced plant community responses or recovery. These findings indicate that while the shortgrass steppe is water limited with drought adapted species, these xeric grassland plant communities are less resistant and resilient to multiyear drought than those in mesic grasslands.Item Open Access Revealing the controls of microbial nitrous oxide (Nâ‚‚O) production and consumption using stable isotope methods(Colorado State University. Libraries, 2021) Stuchiner, Emily R., author; von Fischer, Joseph C., advisor; Baron, Jill, committee member; Cotrufo, M. Francesca, committee member; Knapp, Alan, committee memberOf the three primary anthropogenic greenhouse gases that contribute to climate change, carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), N2O remains the most understudied. While N2O is the least abundant greenhouse gas of the three, it is also the most potent. N2O has a warming potential ~300x greater than CO2 and ~34x greater than CH4, and it is the primary stratospheric ozone depleting substance. Globally, the majority of N2O is emitted from soils through abiotic and microbial processes, but primarily through microbial metabolism. Microbes oxidize or reduce inorganic N as an energy source through different metabolic processes; they emit N2O as a byproduct of these processes. Microbes can also consume N2O by biochemically reducing it to N2, a harmless non greenhouse gas. However, the factors that regulate N2O production and consumption processes are diverse, interactive, and subject to rapid spatial and temporal changes. Drivers of N2O production and consumption include climate features, edaphic properties, and soil microbial community composition and activity. Characterizing these properties in relation to N2O flux behaviors requires a suite of measurements, and the way these factors interact to effect N2O production and consumption remain elusive. Furthermore, isotopic strategies exist to measure different N2O production processes and N2O consumption, but these strategies have been limited in their scope and capacity due to analytical constraints. Together, these challenges have limited our understanding of N2O production and consumption processes. These limitations have made it difficult to robustly disentangle the sources of N2O and understand the importance of N2O consumption in different soils. However, to curtail N2O emissions, we must be able to better understand and anticipate the drivers of N2O fluxes. In my dissertation, I seek to better understand what drives N2O production and consumption in diverse soils. In this work, I deploy innovative methods to measure different N2O production processes, and I seek to more granularly understand what controls N2O consumption. In Chapter 2 I develop a calibration algorithm for a high-throughput, novel, laser-based N2O isotopic analyzer. This allows for direct measurement of diverse microbial N2O-generating source processes. In Chapter 3 I use paired natural abundance and isotopic enrichment approaches to disentangle among N2O production processes more robustly. It will be useful for researchers to deploy paired isotopic strategies to discern more precisely which microbial process(es) are generating N2O. In Chapter 4, I shifted focus from N2O production to better understanding N2O consumption. Here, I sought to stimulate N2O consumption by amending soils with a specific blend of organic acids, and using isotope pool dilution, I learned that microbes consume more N2O when they are freed from electron donor limitation. In Chapter 5, I amended soils with different amounts of organic acids to further explore this electron donor limitation to N2O consumption. I learned that a variety of N2O flux responses can emerge from OC amendment, suggesting that perhaps our understanding of the drivers of N2O reduction are less resolved then we previously might have thought. Human activities have only exacerbated, and are poised to continue to exacerbate, N2O emissions through agricultural practices and industrial activities. There is burgeoning recognition of the importance in managing CO2 and CH4 emissions to mitigate the worst impacts of climate change, but the urgency for N2O, despite its potency and increasing atmospheric emissions, still lags. We must continue to advance understanding of the drivers of N2O production and consumption from soils, and my research makes strides to do this. This will be critical to effectively managing this highly potent greenhouse gas in a global climate that needs to make immediate, and dramatic, greenhouse gas reductions. A proposed Global Denitrification Research Network offers the potential for concerted, coordinated, and systematic N2O research to address the challenge of decreasing N2O emissions.Item Open Access Riparian willow decline in Colorado: interactions of ungulate browsing, native birds and fungi(Colorado State University. Libraries, 2013) Kaczynski, Kristen Mannix, author; Cooper, David, advisor; Jacobi, William, committee member; Knapp, Alan, committee member; Merritt, David, committee memberWillows (Salix spp.) are critical components of Rocky Mountain riparian ecosystems. They provide food for ungulates and beavers; habitat for resident and migratory bird populations, and amphibians; and are integral components of the structure and function of montane riparian ecosystems. In Rocky Mountain National Park (RMNP), willows form the dominant riparian shrub community. However, willow decline over the past 17 years has led to a dramatic change in riparian ecosystems in RMNP, resulting in the conversion of a tall willow community to a community dominated by short willows, with cascading effects on habitat for beaver and migratory and resident songbirds. Research on willow decline has focused primarily on the effects of ungulate browsing and altered hydrologic regimes controlled by beaver populations. However, damage from sapsuckers [woodpeckers] and Cytospora chrysosperma fungal infection are interacting with these known stressors. My dissertation research investigates willow decline using a multifaceted approach and covers three main topics: 1. The biotic and climatic factors contributing to the willow decline; 2. The spatial and temporal dynamics of willow decline; and 3. The effect of altered water tables and increased temperatures on Cytospora fungal infection and willow production. My research provides a comprehensive new understanding of the dynamics of willow decline in RMNP that can be applied to riparian sites throughout the Rocky Mountain ecoregion. My first study explains the, previously unidentified, interaction of sapsucker wounding, Cytospora fungal infection and ungulate browsing in the decline of the riparian ecosystem. My second study demonstrated that the increase in moose populations explained the sharp decline in willows that occurred between 2001 and 2005. Past climate, such as the droughts of the early 2000s, was not the main driver in the decline. Finally, my third study found that willow stems are highly susceptible to fungal infection and my experiment demonstrated that once C. chrysosperma is present on a wound, it will form enlarging cankers under a wide range of environmental conditions. Results from my dissertation research support the conclusion that willow decline is more strongly driven by biotic, rather than climatic stressors. This new understanding of the interactions resulting in willow decline will allow land management agencies to develop more effective restoration strategies.Item Open Access Soil nematode community response to climate change and associated alterations to precipitation and vegetation(Colorado State University. Libraries, 2021) Ankrom, Katharine Elizabeth, author; Wall, Diana, advisor; Fonte, Steven, committee member; Knapp, Alan, committee member; Lockwood, Dale, committee memberUnderstanding of the belowground grassland response to climate change is much more limited than aboveground responses. This disparity in knowledge is partially due to the vast diversity in species in belowground ecosystems and the overwhelming task of identifying the roles and processes associated with each. Soil nematodes represent the most abundant soil fauna on earth and are exceptional in that they occupy every trophic level, contain multiple life history strategies, and are relatively easy to extract and identify from soil. Moreover, nematode activity (e.g. feeding) directly regulates the size and function of fungal and bacterial populations thus indirectly impacting the rates of carbon and nitrogen turnover. Determining the abundance of each nematode genera in a soil sample can allow for calculation of ecological indices that can further explore the trophic complexity, energy pathways, and both the sensitivity and resilience of soil nematode communities to stress and disturbance. Therefore studying soil nematode communities provides a means for gaining important insights about poorly understood belowground responses to altered environments. The aim of this dissertation is to expand our knowledge of soil community dynamics in grasslands in the face of extreme precipitation changes and possible vegetation shifts. In the first chapter of this dissertation, I introduce the importance of grassland ecosystems and the challenges looming from climate change. Next I highlight the two scenarios in which my research is based and give the details on how utilizing nematode data can answer these questions. The second chapter of this dissertation addresses the question: Can nematode trophic analysis reveal associations between vegetation cover types? This study revealed striking differences in the abundances of fungivores and the combined omnivore/predator trophic groups found under the dominant grass compared to both an invasive forb and bare soil cover types. In the third chapter a focus on the most well-studied nematode trophic group; plant parasitic nematodes (PPN) sought to determine if different feeding strategies lead to distinct responses in precipitation treatments across three grassland sites. This research aimed to understand if host plants will have an increased burden harboring greater PPN populations along with increased water stress. Our results showed that the response of PPN feeding type abundance, functional guild, and herbivory index to precipitation was site dependent, a finding not previously studied. Building on the findings of Chapter 3, Chapter 4 utilized the entire soil nematode community and calculated indices to see how the different grassland types; arid, semiarid, and mesic would respond to the same precipitation treatments. Specifically, I tested if nematodes would be effective indicators of the soil community to changes in rainfall events. The results of this study showed the importance of genera level resolution and suggests that the sensitivity of these indices allows for ecological interpretation of belowground function and status in a natural setting. A finding that is especially pertinent, as these grasslands will not respond to precipitation alterations similarly and will therefore require unique mitigation strategies. In summary, with both field and laboratory work my PhD project has: 1) found associations between nematode trophic group abundance and vegetation cover types; 2) revealed the different response of grassland ecto-and endoparasitic nematodes to manipulated rainfall across a precipitation gradient; 3) quantified the herbivory index of a PPN population in response to precipitation treatments across three grassland sites; and 4) demonstrated the sensitivity of nematode ecological indices and found indicator genera in three grassland sites with manipulated precipitation treatments. Together these results bolster our knowledge of how soil nematode communities will respond to climate change and highlight their potential role for monitoring and influencing grassland ecosystem dynamics into the future.Item Open Access Using species functional traits to predict community dynamics(Colorado State University. Libraries, 2012) Ames, Gregory Michael, author; Webb, Colleen, advisor; Poff, N. LeRoy, committee member; Knapp, Alan, committee member; Noon, Barry, committee memberA major goal for community ecology has been to determine a general set of rules to explain the structure and function of communities. Traits-based methods for describing community dynamics have been touted as providing a set of general methods to describe the structure and function of communities based on measurable properties of individual organisms in the community in a changing environment. Validation of traits-based methods that describe changes in community structure as a function of the interaction between functional traits along changing environmental gradients in real systems is needed. Here we present studies of three different plant communities where we use novel applications of traits-based Bayesian hierarchical models and principal component analysis to explain the changes in community structure/function and demonstrate that the communities are primarily structured by traits and their interactions with a changing environment. In a natural tallgrass prairie we were able to explain more than 84% of the variation in community functional diversity and an average of 64% of the cover variation across the ten species in the study over a 25-year span (Chapter 1). Additionally we show that changes in community structure are primarily explained by relative growth rate and its interaction with precipitation. In an experimentally manipulated grassland, our model explains more than 75% of the variation in total plot biomass over the course of 18 years. Further, we found that this system was primarily driven by the same trait/environment interactions as the tallgrass system. Finally, we show that trait/environment interactions allow us to explain 91% of the variation in plot biomass in a restored riparian wetland. Our ability to explain large portions of the variation in community structure and performance of these three distinct types of plant communities, using similar traits and environmental drivers, provides evidence of general laws underlying the structure of plant communities. This work represents a significant step toward understanding those general laws and helping community ecology develop from a largely descriptive science to a predictive science.Item Open Access What's the story? The effects of narratives in science classrooms(Colorado State University. Libraries, 2018) Leipzig, Peter, author; Balgopal, Meena, advisor; Ode, Paul, advisor; Doe, Sue, committee member; Knapp, Alan, committee memberWhile effective science communication is crucial, it also presents multiple obstacles for natural science researchers and specialized communicators. This includes a language divide between scientists and the general public, making science less approachable to novices. The use of narratives within science represents a powerful strategy for overcoming these issues. We examined the reported effects of narratives as a communication strategy and reviewed the varying definitions of narratives in the literature. We propose a set of essential elements that differentiate narrative communication from other forms, all of which are useful for researchers seeking to understand the impacts of stories. These elements include events, characters, causality/agency, and conflict/resolution. We also studied the effects of training graduate teaching assistants (GTAs) using narrative communication. We examined i) what narrative elements GTAs incorporated into their own lessons, ii) why they chose to include stories in their classes, and iii) how training affected content knowledge and self-perceptions for GTAs and their undergraduate students. We found that GTAs who were trained using stories were more likely to integrate the narrative elements into their lessons. Additionally, when employing narratives, GTAs focused on the process of science rather than the results. However, the GTAs did not demonstrate or perceive any concrete knowledge gains. Finally, we argue that narratives can and should be incorporated into more introductory courses across multiple disciplines.