Browsing by Author "Poff, N. LeRoy, advisor"
Now showing 1 - 9 of 9
- Results Per Page
- Sort Options
Item Open Access Aquatic insect responses to predation and temperature: variation in context dependent trophic interactions(Colorado State University. Libraries, 2017) Morton, Scott Gregory, author; Poff, N. LeRoy, advisor; Kondratieff, Boris, committee member; Schmidt, Travis, committee memberTrophic cascades, the indirect effects of carnivores on primary producers mediated by herbivores, remains a central theme of ecological theory. How climate change will alter the mechanisms controlling such interactions remains largely unexplored, certainly in stream ecosystems. In montane streams, stonefly predators have been documented to indirectly affect algal biomass by influencing the distribution, abundance, behavior, and life histories of invertebrate grazers. Density mediated indirect interactions (DMII) occur when primary producer biomass is primarily influenced by changes in herbivore abundance due to consumption by predators. Trait-mediated indirect interactions (TMII) alter primary producer abundance through non-consumptive interactions such as anti-predatory behaviors. In this research, I conducted mesocosm experiments on stonefly predators and mayfly prey to determine the relative importance of grazers on regulating algal production under three temperature treatments intended to simulate climate warming. Furthermore, I examined the influence of both DMII and TMII on algal production through consumptive and non-consumptive predatory treatments. I found algal biomass to decrease as temperature increased, however found no differences among grazer-alone treatments versus DMII or TMII on algal production.Item Open Access Aquatic insect β-diversity among small mountain headwater streams and the role of multiple mechanisms maintaining community structure(Colorado State University. Libraries, 2014) Harrington, Rachel Anne, author; Poff, N. LeRoy, advisor; Kondratieff, Boris, committee member; Ghalambor, Cameron, committee memberDespite lower local richness (α-diversity), individual headwater tributaries often retain highly distinct aquatic insect communities (β-diversity) within the overall river network. This trend is presumed especially true among high-elevation streams; where high β-diversity is driven by the effects of steep topography and harsh climatic conditions limiting dispersal between isolated mountaintop "islands." However, inference has been predominantly drawn from observed trends along single-thread channels (higher-elevation headwaters through lower-elevation mainstems); and the increased size and hydrologic connectivity accompanying lower-elevation mainstems provide potential alternative explanations for this pattern. Controlling for habitat size, I sampled aquatic insect communities in 24 headwater streams from three adjacent river drainages spanning 2000-3500 m in elevation. I measured β-diversity among streams within each drainage (community turnover- β across elevation) and β-diversity across drainages (community dissimilarity- β within elevation "zones"). Turnover- β across elevation was consistently high and displayed no trend. Additionally, dissimilarity-β across drainages was not significantly different between high-elevation and low-elevation zones. These results provide the first evidence that β-diversity among low-elevation headwater communities is equivalent to communities at high-elevations. Evidence suggests that high β-diversity among small headwater streams is attributed to low habitat connectivity and/or to high habitat heterogeneity, resulting from their isolated position within the dendritic network and strong responses to the surrounding environment. In order to disentangle the role of multiple mechanisms maintaining β-diversity, I utilized the unique landscape of mountain ranges, exhibiting steep gradients of spatial distance, local environmental conditions, and disturbance regimes. I characterized all 24 sites using explanatory variables categorized into spatial predictors (describing geographic location), environmental predictors (describing local habitat), and flow regime predictors (describing potential disturbances overtime). Using a series of redundancy analyses (RDA) I tested the ability of each categorized predictor group to significantly explain variation in community structure among those sites within a drainage and among those sites within an elevation zone. Further, original communities were partitioned into unique assemblages distinguished by the presence/absence of key ecological traits. Using interpretation of potential underlying mechanistic processes, I tested a priori hypotheses regarding the change in relationship between trait-partitioned assemblages. Results determined that although environmental predictors best explained community turnover-β within drainages, they were unable to explain community dissimilarity-β within any elevation zone, where habitat heterogeneity is presumably lower and inter-site network distance is higher. Additionally, dissimilarity-β among high-elevation communities was only explained by spatial predictors, supporting previous hypotheses that these communities are isolated by distance, while community dissimilarity-β among low-elevation sites was only explained by flow regime predictors. Overall, these findings suggest that despite consistent patterns in β-diversity, the relative role of mechanisms maintaining this diversity is context dependent, presenting important implications regarding the successful conservation of these dynamic systems.Item Embargo Changes in functional structure of aquatic insect communities across environmental gradients in mountain streams(Colorado State University. Libraries, 2024) Gutierrez, Carolina, author; Poff, N. LeRoy, advisor; Ghalambor, Cameron, advisor; Neuwald, Jennifer, committee member; Webb, Colleen, committee memberThis study investigates the functional diversity of aquatic insect communities across environmental gradients within Rocky Mountain headwater streams, aiming to better understand how elevation, water temperature, and canopy cover shape the structure and dynamics of these communities. Functional diversity (FD) is defined here as the range, distribution, and relative abundance of organismal traits, which together provide deeper insight into ecosystem functionality than species diversity alone. FD was quantified through three primary metrics: functional richness (FRic), functional evenness (FEve), and functional divergence (FDiv), each capturing distinct aspects of how species contribute to ecosystem functioning. This multidimensional approach enables a nuanced examination of how aquatic insect communities respond to various environmental stressors and spatial constraints, particularly as altitudinal changes present unique challenges in terms of temperature variability and resource availability. Field data were collected from twenty-four stream sites distributed across elevation bands ranging from 1,500 to 3,500 meters. Sites were replicated in three different drainage systems to account for regional variation, with insect specimens collected and assessed for twenty functional traits. These traits included parameters such as voltinism (number of life cycles per year), adult lifespan, emergence synchronization, and dispersal ability, all of which are critical in determining an insect's role in the ecosystem. Canopy cover and water temperature were also measured to evaluate how localized microclimates and light availability influenced community composition. Results revealed a significant decline in functional richness with increasing elevation, with the steepest reductions observed in streams with sparse canopy cover. Functional richness was highest in areas where canopy cover ranged between 65-78%, and water temperature was between 8°C and 15°C, suggesting that moderate canopy cover and specific thermal conditions support more functionally diverse communities. Functional evenness and divergence, while showing less pronounced patterns, indicated that the most extreme trait values are critical for resilience in these systems, particularly under fluctuating environmental conditions. Trophic interactions further illustrate the importance of specific functional groups, such as predators, grazers, and filterers, in shaping community structure. The analysis of beta diversity demonstrated substantial turnover in functional traits across elevation gradients, emphasizing the heterogeneity of insect communities within low-order, high-altitude streams and reinforcing the role of environmental filtering in community assembly. These findings highlight the vulnerability of headwater stream ecosystems to environmental changes and underscore the importance of functional diversity metrics in ecological monitoring and conservation efforts. Overall, this study contributes to our understanding of how functional environmental gradients structure diversity and provides a foundation for comparative studies on functional diversity in tropical versus temperate mountain stream ecosystems, particularly in the context of global biodiversity conservation.Item Open Access Changes in taxonomic and functional diversity of aquatic macroinvertebrates along a gradient of stream size and flow stability in the northeastern Colorado Rocky Mountains(Colorado State University. Libraries, 2018) Lafferty, M Holliday, author; Poff, N. LeRoy, advisor; Kondratieff, Boris, committee member; Kampf, Stephanie, committee memberWhile the pattern of aquatic macroinvertebrate communities along stream size gradients have been examined in past studies, it is usually in the context of the river continuum, moving along a stream network from the headwaters to large rivers. The effect of stream size among small headwater streams has received less attention. With increasing temperatures and decreasing snowfall predicted in the Colorado Rockies, streams in the area are likely to decrease in size and have an increased likelihood of flow cessation in especially dry years. To understand how these changes will affect aquatic macroinvertebrate communities, this study explored differences in species occurring in streams of differing size and flow stability. I examined the taxonomic and functional diversity of aquatic macroinvertebrates in 12 headwater streams in the Cache la Poudre watershed of northern Colorado. Each stream was assigned a stream “type” based on size (measured by discharge and drainage area) and the stability of the flow throughout the summer. My results show that size was positively correlated with both taxonomic and functional richness. I found that the large streams with intermediate stability and small streams with stable flow had greater taxa and functional richness than did the small streams with intermediate flow and small streams with unstable flow, illustrating that flow stability is also important in determining macroinvertebrate communities. Certain species functional traits, such as inhabiting erosional zones and filter-feeding were found to be associated with increasing stream size and stability. I calculated β-diversity across the size and stability gradient and found that replacement of taxa (turnover) better explained among-site differences than did addition of taxa (nestedness). The specific taxa that prefer smaller streams were identified with indicator species analysis. Overall, these results indicate that the hotter and drier summers predicted by climate change models may lead to decreases in overall macroinvertebrate taxa and functional richness and potentially cause displacement of taxa as the smallest headwater streams become less stable.Item Open Access Investigating experimental and environmental factors to provide a mechanistic understanding of benthic algal biomass accumulation in freshwater streams(Colorado State University. Libraries, 2019) Beck, Whitney S., author; Poff, N. LeRoy, advisor; Hall, Ed, committee member; Hoeting, Jennifer, committee member; Spaulding, Sarah, committee memberTo view the abstract, please see the full text of the document.Item Open Access Modeling riparian vegetation responses to flow alteration by dams and and climate change(Colorado State University. Libraries, 2013) Auerbach, Daniel Albert, author; Poff, N. LeRoy, advisor; Bledsoe, Brian, committee member; Boone, Randall, committee member; Merritt, David, committee member; Webb, Colleen, committee memberAs the interface between freshwater and terrestrial ecosystems, riparian vegetation is a critical influence on biodiversity maintenance and ecosystem service production along river corridors. Understanding how altered environmental drivers will affect this vegetation is therefore central to sound watershed management. A river's flow regime exerts a primary control on the type and abundance of riparian vegetation, as differing adaptations to changing discharge levels mediate plant recruitment and persistence. Models of the relationships between flow and vegetation, generalized across species in terms of flow response traits such as flood tolerance, provide a means to explore the consequences of hydrologic alteration resulting from dams and climate change. I addressed these issues through development of a stage-structured model of woody riparian vegetation driven by variation in annual high flows. Simulation experiments offered insight into the potential trajectories of competing vegetation trait types relative to scenarios of dam construction, re-operation and removal. Modifying the size and frequency of the floods responsible for both disturbance mortality and establishment opportunities altered the relative abundance of pioneer and upland cover. Yet, qualitative differences in simulated outcomes resulted from alternative assumptions regarding seed limitation and floodplain stabilization, illustrating the need to carefully consider how these factors may shape estimated and actual vegetation responses to river regulation. In addition, I linked this simulation approach with an integrated watershed-modeling framework to assess the relative risk of invasion by the introduced plant Tamarix under multiple climate change scenarios. Though warming may increase the potential for Tamarix range expansion by weakening thermal constraints, the results of this work supported the expectation that hydrogeomorphic variation will control how this potential is realized. With simulated invasion risk strongly dependent on shifts in both the magnitude and timing of high flows, model outcomes underscored the importance of accounting for multiple, interacting flow regime attributes when evaluating the spread of introduced species in river networks. This research suggested the utility of simplified but process-based simulations of riparian flow-ecology relationships, demonstrating that such models can establish a first approximation of the potential consequences of management decisions and can highlight key questions for additional research, particularly where data are scarce and uncertainty is high.Item Open Access Regional methods for evaluating the effects of flow alteration on stream ecosystems(Colorado State University. Libraries, 2012) Wilding, Thomas K., author; Poff, N. LeRoy, advisor; Bledsoe, Brian, committee member; Sanderson, John, committee member; Steingraeber, David, committee memberThree stand-alone chapters explore the development and implementation of regional flow-ecology methods. Ecohydrology is an interdisciplinary field that brings together specialized research in hydrology, hydraulics, geomorphology and ecology. My dissertation reflects the need for interdisciplinary knowledge, tackling issues as diverse as low flows for trout (Chapter 2) to peak flows for cottonwood (Chapter 3). A regional-scale view unifies these investigations, with Chapter 1 establishing the scientific foundation and management objectives for regional flow-ecology methods. Summary Chapter 1 - To balance the benefits of dams and water diversions against society's expectations for the natural environment, flow managers require scientific advice on the ecosystem response to flow alteration. The methods selected to investigate the ecosystem effects of flow alteration (e.g., PHABSIM - Physical Habitat Simulation) should reflect the scale of flow management and the information requirements of flow managers. In addition, a hierarchical habitat framework provides an ecological foundation for the development and implementation of flow-ecology methods, because ecosystem response to flow is constrained by large-scale processes. This can be put into practice using hydrogeomorphic classification to define the higher-level physical processes (e.g., sediment transport, disturbance) that dictate the mechanisms of biotic response to flow. Regional flow-ecology methods provide a vehicle for incorporating prior knowledge and hydrogeomorphic processes into flow management at both regional and local scales. Chapter 2 - Changes in hydraulic habitat (depth and velocity) with flow can be predicted using intensive reach-specific methods, such as PHABSIM. I used existing PHABSIM data to develop GHMs (Generalized Habitat Models) that predict trout habitat-flow curves for unsurveyed streams of the southern Rocky Mountains. Predicted habitat was significantly correlated with the abundance of large brown trout (P<0.01), but not smaller trout (using Colorado Division of Wildlife monitoring data). The rapid-survey GHM (from channel width) represents a major reduction in survey effort compared to a full PHABSIM survey, and produced better predictions of observed habitat than the desktop GHM (from mean annual flow). Chapter 3 - Cottonwood trees are valued members of riparian ecosystems and, in the drier areas of North America, their recruitment depends on high flow events. To help plan for anticipated increased water demand, the ELOHA framework was used to develop flow-ecology relationships for three basins in Colorado (total area 53,000 km2). Existing data revealed a negative relationship between the abundance of plains cottonwood (Populus deltoides Bartram) and reduced peak-flows. The hypothesis that this flow constraint would also apply to a second species, narrowleaf cottonwood (Populus angustifolia James), was not supported because four reaches (out of the 39 surveyed) had abundant and reproducing narrowleaf forest, despite pronounced flow alteration (>40% flow reduction). Historic photographs revealed that narrowleaf in the Middle Park area (Colorado) have increased in abundance since dam closure, colonizing previously bare gravel bars. That narrowleaf appear less sensitive to flow alteration than plains cottonwood could reflect different species traits (e.g., alternative sources of disturbance for root suckering by narrowleaf), together with the many physical transitions from plains to mountains that are associated with the species transition.Item Open Access Socio-environmental tradeoff analysis using decision science tools to guide river management(Colorado State University. Libraries, 2015) Martin, David M., author; Poff, N. LeRoy, advisor; Labadie, John W., committee member; Loomis, John B., committee member; Sanderson, John S., committee memberAcross the globe, rivers are put into the service of meeting human needs and wants. Societal dependence on rivers and the consumptive benefits they provide has advanced at the unanticipated cost of degrading biodiversity and river ecosystem function. Socio-environmental tradeoff analysis is key to balance disparate interests for sustainable river management. Multi-criteria decision analysis (MCDA) is a sub-discipline of decision science methods that aid decisions to resource management problems with multiple conflicting criteria and management alternatives. Techniques for MCDA are useful for tradeoff analysis but they are uncommonly used for river management, especially case studies based on incorporating the principles of river restoration into watershed management. I explore the qualitative and quantitative capabilities of MCDA with four stand-alone chapters that take a decision science approach towards balancing socio-environmental interests for large scale river management. Together, these chapters make a contribution toward bridging the gap between empirical freshwater science and normative decision making.Item Open Access The distribution of lotic insect traits in relation to reference conditions and projected climate change in the western United States(Colorado State University. Libraries, 2014) Pyne, Matthew Ivern, author; Poff, N. LeRoy, advisor; Bledsoe, Brian P., committee member; Hoeting, Jennifer A., committee member; Webb, Colleen T., committee memberThe use of species traits (e.g., life history, morphological, physiological, or ecological characteristics of an organism) to describe community responses to environmental change has become a common practice in stream ecosystems, with over 900 papers describing macroinvertebrate trait-environment relationships in streams. The use of traits provides some advantages over traditional taxonomic metrics, such as providing a mechanistic link between an organism and its environment, but also presents some challenges, such as many traits being correlated with other traits and multiple environmental variables. Various methods have been recommended to address these challenges, such as using multiple traits, posing a priori hypotheses, and evaluating streams across large-spatial scales. The vast majority of studies have not incorporated these recommendations, however, particularly in North America. My research had two general objectives: 1) describe the dominant trait-environmental relationships in natural streams in the western United States and 2) use two distinct traits-based methods to evaluate how stream aquatic insect communities are currently distributed in terms of multiple environmental variables and how species and communities may respond to climate change. Traits are often used to evaluate the ecological integrity of streams and a baseline understanding of aquatic insect trait-environment relationships is needed for the western United States. I used logistic regression, multinomial regression, and redundancy analysis to explore the relationships between 20 trait distributions and 83 environmental variables in 253 least-disturbed streams across 12 western states. Traits had the strongest relationships with regional climate and local stream habitat conditions (e.g., air temperature, conductivity, mean annual runoff) rather than elevation, land use, or measures of extreme hydrological events. Traits such as thermal tolerance, size, swimming strength, rheophily, voltinism, and armoring exhibited strong relationships with the environmental data and would be ideal for large-scale stream assessments. Aquatic insect communities contain many taxa that are sensitive to temperature increases and changes to runoff. Two traits, cold water preference and erosional obligate (i.e., needs to live in fast-water habitat) have been used in the past to estimate the effect of climate change on stream insect communities, but no study has accounted for both climatic and non-climatic effects on these two traits. I developed a Bayesian path analysis describing how the distributions of these two traits respond to multiple environmental gradients, not just temperature, and discovered that the distribution of cold-adapted taxa was strongly correlated with changes in air temperature in the wet, cool ecoregions, but was correlated with thermal buffers and refuges in most dry, warm ecoregions, indicating that temperature-sensitive taxa are likely on the brink of their thermal tolerance in those ecoregions. A second approach to assess community sensitivity to climate change is to determine the specific thermal tolerance of each taxon individually. I computed the thermal and stream runoff thresholds of common stream taxa and compared the World Climate Research Programme's climate model predictions to these thresholds. I found that the stream communities most at risk to climate change were found in some dry ecoregions, concurring with the previous results, and in wet, warm ecoregions with a high proportion of spatially restricted and endemic taxa, such as northern California. These two approaches describe possible mechanisms of climate change resistance and identify sensitive ecoregions.