Theses and Dissertations at Montana State University (MSU)
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Item Macroinvertebrate diversity, community structure, and dispersal are affected by tributary identity and confluence conditions in a regulated river(Montana State University - Bozeman, College of Letters & Science, 2023) Maguire, Zachary John; Chairperson, Graduate Committee: Lindsey Albertson; This is a manuscript style paper that includes co-authored chapters.Tributaries are essential components of freshwater ecosystems, playing a crucial role in maintaining connectivity and providing habitat for a diverse array of aquatic organisms. The role of tributaries in creating heterogeneity in physical conditions and food resources for fishes could be critical, yet little is known about how variable conditions in different tributaries in regulated river systems influence the mainstem. Using field observations in five tributaries on the Madison River, Montana, we found that tributaries in the same network and within relatively short distances of 60km varied greatly in their environmental conditions, macroinvertebrate densities, and macroinvertebrate community structure. Downstream of confluences macroinvertebrate richness increased overall, and per capita weight of drifting macroinvertebrates decreased overall. These findings suggest that confluences may act as hotspots for biodiversity in regulated rivers and introduce smaller bodied macroinvertebrates to the drift. The amount that a tributary influenced benthic richness and mean per capita weight in the drift downstream of its confluence was related to land use and abiotic factors within that tributary; both macroinvertebrate metrics significantly increased in magnitude downstream of confluences with higher percentage of US Forest Service land, cooler temperatures, decreased discharge, and increased elevation loss (i.e. steeper watershed slope). In contrast, tributaries that had a larger proportion of agricultural land, warmer temperatures, and higher discharge more strongly influenced benthic macroinvertebrate metrics. These tributaries supported higher benthic density and biomass downstream of confluences. Our results offer insight into the ways that tributaries can create heterogeneous habitats that in turn structure macroinvertebrate communities in mainstem rivers and suggest that conservation and restoration of these essential components of freshwater ecosystems is a well-spent endeavor in rivers with regulated mainstems. Future research will need to test the ubiquity of the patterns we observed in other river networks and under other global changes such as pollution, invasive species, and drought. Continued understanding of the importance of heterogeneity imparted by tributaries and their confluences on diversity, availability, and quality of food for threaten fishes is needed to guide restoration efforts aimed at improving river condition and resilience.Item Positive effects of ecosystem engineers on stream communities and processes(Montana State University - Bozeman, College of Letters & Science, 2022) Tumolo, Benjamin Bartley; Chairperson, Graduate Committee: Lindsey Albertson; This is a manuscript style paper that includes co-authored chapters.Ecosystem engineering is a process by which organisms modify habitat characteristics and influence community structure and ecosystem function. These engineer-mediated habitat modifications often have positive effects on community members by improving or creating novel habitats that ameliorate harsh conditions. Despite the far-reaching consequences of such positive interactions, most of what we know about ecosystem engineering is limited to marine or terrestrial habitats and focused on sessile, long-lived foundation species. Less recognition has been given to mobile, smaller bodied, and shorter-lived insect engineers within freshwater ecosystems. This knowledge gap is significant as freshwaters are one of the most threatened habitats globally, and freshwater insects are experiencing alarming rates of decline. My dissertation seeks to uncover how organism interactions modify physical and resource environments in ways that can affect community structure and ecosystem function. My objectives were to: 1) synthesize literature to develop a conceptual framework aimed at describing how two distinct mechanisms of positive interactions scale over time and space; 2) measure how net-spinning caddisfly (Hydropsychidae) engineers and their abandoned engineering structures differentially facilitate communities; 3) quantify the importance of beneficiary functional traits and environmental gradients in determining the strength of facilitation between caddisflies and invertebrate communities; and (4) test how caddisflies can generate hotspots of community assembly and ecosystem function. I found that caddisfly ecosystem engineers and their abandoned structures increased invertebrate colonization; however, occupied structures supported greater colonization of Chironomidae compared to abandoned structures. Additionally, I found that the strength of caddisfly facilitation increased with increasing elevation and was dependent on small-bodied beneficiaries. Furthermore, I found that caddisfly engineers generated ecological heterogeneity by aggregating both resources and consumers, with consequences for elemental cycling. Overall, my dissertation emphasizes the role that biology can play in modifying environments and how these alterations can positively influence biological communities with consequences for ecosystem function.Item Ecosystem engineering at the streambed: how net-spinning caddisflies influence substrate flow dynamics(Montana State University - Bozeman, College of Letters & Science, 2020) MacDonald, Michael Joseph; Chairperson, Graduate Committee: Lindsey Albertson; Lindsey K. Albertson and Geoffrey C. Poole were co-authors of the article, 'Ecosystem engineering at the streambed: how net-spinning caddisflies influence substrate flow dynamics' submitted to the journal 'Ecohydrology' which is contained within this thesis.The streambed is an ecotone between surface waters and underlying hyporheic systems. Identifying the controls on advective flow through this ecotone is critical to understanding the movement of energy and matter in streams. Hydropsychids (net-spinning caddisflies) are aquatic macroinvertebrate ecosystem engineers that influence streambed cohesion, yet evidence of direct influence on hydrologic processes is lacking. Utilizing a novel downward flow permeameter, we demonstrate how net-spinning caddisfly colonization of the streambed interstitia at moderate but common densities (2,000 m^-2) can reduce the vertical hydraulic conductivity (KV) by up to 55% in coarse sand and gravels (median diameter = 12.91 mm). Sediment columns incubated in artificial stream water occupied by caddisflies showed greater reductions in KV relative to those without caddisflies. Additionally, organic matter content within sediment columns showed that occupation by caddisflies resulted in nearly two-fold increases in organic matter AFDM. Our research shows that the ubiquitous and numerous net-spinning caddisflies are likely to modulate the exchange of channel and hyporheic water by constructing nets in open pore spaces, increasing flow resistance, and decreasing flow velocities, as well as stimulating organic matter deposition with potential consequences for biofilm growth. These results suggest that caddisfly induced reductions to flow may influence transfer processes occurring at the streambed ecotone, altering biogeochemical processes in streams.Item Influence of thermal regime on the life histories and production of Rocky Mountain aquatic insects(Montana State University - Bozeman, College of Letters & Science, 2019) McCarty, Jennifer Denise; Chairperson, Graduate Committee: Wyatt F. CrossLife history traits of aquatic insect taxa such as metabolism, terminal body size, and fecundity vary along natural thermal gradients. Body size, in particular, is expected to respond to temperature and may have important consequences for fecundity and the production of insects. The Thermal Equilibrium Hypothesis (TEH) predicts that aquatic insect taxa are most abundant at an intermediate 'optimal' temperature where life history traits such as terminal body size and reproductive potential are maximized, i.e., the thermal 'optimum'. A competing hypothesis, the Temperature Size Rule (TSR), predicts that individuals developing at the coldest temperatures in their range will grow more slowly, but attain the largest body sizes and therefore exhibit greater fecundity than individuals growing at warmer temperatures. Implicit in both of these theories is that population-level production, a measure of population 'success', will be greatest where terminal body size and fecundity are maximized. Few studies have investigated the TEH in the field, and none have measured the relationship between production and other life history traits in the context of these theories. Our study focused on three common Rocky Mountain aquatic insect taxa: Drunella doddsii, Hydropsyche cockerelli, and Ephemeralla infrequens. We quantified the influence of thermal regime on growth rates, terminal body size, reproductive potential, and population-level biomass and production, all of which potentially limit the longitudinal distribution and success of these taxa. We found that growth varied strongly with season and site, leading to significant variation in the timing of growth and terminal body size. Reproductive potential was negatively associated with mean annual temperature as predicted by the TSR. Unexpectedly, reproductive potential was not always correlated with terminal body size. Population density, biomass, and secondary production were generally positively correlated with terminal body size for D. doddsii and H. cockerelli, as expected from both predictive models. In contrast, these relationships were not as consistent for E. infrequens. Our findings provide new insight as to how thermal variation influences the ecology of aquatic insects in the context of the TEH and TSR. Our results should be valuable for predicting population and community responses to ongoing changes in climate.Item The effects of temperature on stream ecosystem structure, secondary production, and food web dynamics(Montana State University - Bozeman, College of Letters & Science, 2019) Junker, James Robert; Chairperson, Graduate Committee: Wyatt F. Cross; Wyatt F. Cross, Jonathan P. Benstead, Alexander D. Huryn, James M. Hood, Daniel Nelson, Gísli M. Gíslason and Jón Ólafsson were co-authors of the article, 'Patterns and drivers of ecosystem-level biomass and stoichiometry in streams' submitted to the journal 'Ecosystems' which is contained within this thesis.; Wyatt F. Cross, Jonathan P. Benstead, Alexander D. Huryn, James M. Hood, Daniel Nelson, Gísli M. Gíslason and Jón Ólafsson were co-authors of the article, 'Resources govern the temperature-dependence of animal production at multiple timescales' submitted to the journal 'Ecology letters' which is contained within this thesis.; Wyatt F. Cross, Jonathan P. Benstead, Alexander D. Huryn, James M. Hood, Daniel Nelson, Gísli M. Gíslason and Jón Ólafsson were co-authors of the article, 'Responses of food web organic matter fluxes to temperature and their implications for food web stability' which is contained within this thesis.Since 1880, Earth's mean temperature has risen ~0.85 °C, and increases >1.5 °C are likely by the end of the 21st century. Warming temperatures will continue to shuffle and restructure ecological communities and the consequences of these changes for ecosystem processes and services are largely unknown because of the difficulties in measurement and understanding in complex ecological systems. Yet, isolating temperature's influence is crucial to predicting how ecosystems will look and operate in a 'no-analog' future and to begin to integrate warming with the myriad other stressors affecting natural systems. In this dissertation, I leverage a natural stream temperature gradient (~5 - 25 °C) within a geothermal watershed to investigate the effects of temperature on stream ecosystems--with three specific questions: 1) what is the relative influence of temperature and stream flow on whole-ecosystem biomass and element storage? 2) how does temperature shape patterns of animal production across and within streams? and 3) how does temperature modify the seasonal patterns of consumer-resource interactions in stream food webs? I found stream flow to have primacy in driving the 2 orders of magnitude variation in ecosystem biomass and element storage--mediated through flow's effect on plant body size. At higher trophic levels, temperature strongly shaped the patterns of secondary production coinciding with a 45-fold increase in annual secondary production across streams. This positive relationship was mediated through covariation between temperature and basal resource availability, both across and within streams. Consumer interactions with basal resources showed differing seasonality with increasing temperature. At higher temperatures, consumer demand and resource availability were strongly coupled seasonally compared to cooler streams. Tighter coupling between consumers and resources with temperature lead to more consistent, if higher, interaction strengths through the year. My work shows temperature as an important structuring driver of ecosystem structure and process, however, a common thread through each chapter shows the influence of temperature is mediated through its interactions with other ecosystem drivers. Ultimately, as the covariation between temperature and other environmental drivers (e.g., disturbance, nutrient and light availability, etc.) shift globally, recognizing these interactions is increasingly important.Item The benthos and drift fauna of a riffle in the Madison River, Yellowstone National Park(Montana State University - Bozeman, College of Agriculture, 1966) Heaton, John R.Item Trophic basis of invertebrate production in a Northern Rockies stream with recent willow recovery(Montana State University - Bozeman, College of Letters & Science, 2011) Junker, James Robert; Chairperson, Graduate Committee: Wyatt F. CrossEcologists have long recognized that ecosystems are not isolated in the landscape and can receive inputs of energy, materials, and organisms from beyond their boundaries. The role of these inputs for consumers in receiving ecosystems depends on biotic and abiotic characteristics of both the donor and recipient ecosystems. In streams, the influence of leaf litter input from terrestrial environments on stream structure and function has received much study. Recently, riparian vegetation in Yellowstone National Park has undergone increases in growth and distribution in many areas, however the implications for food webs of adjacent stream ecosystems has remained unexplored. In this study, we combined stable isotope ratios of food web components with estimates of invertebrate secondary production to measure the relative importance of terrestrial organic matter and algae to stream invertebrate production. We found stable isotope ratios of terrestrial litter were relatively constant throughout the annual cycle. In contrast, algae showed varying patterns of enrichment and depletion likely driven by changes in light, discharge, and sources of dissolved carbon and nitrogen. Mean annual secondary production was 7.5 g AFDM m -² y -¹ (95% CI; 7.0-8.2), and the majority of this production was supported by stream algae (58%; terrestrial detritus supported 42%). Invertebrate production varied seasonally, with >50% of annual production occurring between July and September. Relatively high quality algae supported the majority of production during this critical growth period characterized by warm temperatures and high NPP. Terrestrial litter supported the majority of invertebrate production (57%) during cold months between October and May, when stream NPP and metabolic demands of invertebrate consumers were low. Our findings demonstrate that high quality resources support invertebrate production during periods of high metabolic demand, while terrestrial litter provides an abundant resource to support invertebrate consumer production when higher quality resources are scarce and metabolism is reduced. This study provides a quantitative measure of the importance of allochthonous and autochthonous resources to an invertebrate community of a northern Rocky Mountain stream, and provides a benchmark to assess the potential impacts of changing riparian vegetation on streams within the northern Rocky Mountains.