Scholarship & Research
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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 African wild dog demography in an ecosystem with reduced prey and dominant competitors(Montana State University - Bozeman, College of Letters & Science, 2021) Goodheart, Benjamin Michael; Chairperson, Graduate Committee: Scott Creel; Scott Creel, Matthew S. Becker, Milan Vinks, Kambwiri Banda, Carolyn Sanguinetti, Paul Schuette, Elias Rosenblatt, Chase Dart, Anna Kusler, Kim Young-Overton, Xia Stevens, Alstone Mwanza and Chuma Simukonda were co-authors of the article, 'Low apex carnivore density does not release a subordinate competitor when driven by prey depletion' in the journal 'Biological conservation' which is contained within this thesis.Conservation of competitively subordinate carnivores presents a difficult challenge because they are limited by dominant competitors. Prey depletion is one of the leading causes of large carnivore decline worldwide, but little is known about the net effect of prey depletion on subordinate carnivores when their dominant competitors are also reduced. African wild dogs are often limited by high densities of dominant competitors, particularly lions. We measured African wild dog density and survival, using mark-recapture models fit to 8 years of data from 425 known individuals in the Greater Kafue Ecosystem, Zambia. The GKE is affected by prey depletion, particularly of large herbivores, and thus the density of lions is significantly lower than ecologically comparable ecosystems. Counter to expectations from mesopredator release theory, wild dog density in GKE was far lower than comparable ecosystems with higher lion and prey density, though annual survival rates were comparable to large and stable populations. Average pack size was small and home range size was among the largest recorded. Our results show that low lion density did not competitively release the GKE wild dog population and we infer that the low density of wild dogs was a product of low prey density. Our results suggest that there is an optimal ratio of prey and competitors at which wild dogs achieve their highest densities. This finding has immediate implications for the conservation of the endangered African wild dog, and broad implications for the conservation of subordinate species affected by resource depletion and intraguild competition.Item Climate-fire-vegetation dynamics in the Greater Yellowstone Ecosystem: recent trends and future projections in a changing climate(Montana State University - Bozeman, College of Letters & Science, 2020) Emmett, Kristen Dawn; Co-chairs, Graduate Committee: Benjamin Poulter and David Roberts; Katherine M. Renwick and Benjamin Poulter were co-authors of the article, 'Disdentangling climate and disturbance effects on regional vegetation greening trends' in the journal 'Ecosystems' which is contained within this dissertation.; Katherine M. Renwick and Benjamin Poulter were co-authors of the article, 'Adapting a dynamic vegetation model for regional biomass, plant biogeography, and fire modeling in the western U.S.: evaluating LPJ-GUESSLMFIRECF' submitted to the journal 'Ecological modelling' which is contained within this dissertation.; Benjamin Poulter was a co-author of the article, 'Processed-based modeling approaches for climate-vegetation-fire feedbacks in the Greater Yellowstone Ecosystem' which is contained within this dissertation.Climate change threatens to change forested ecosystems and wildfire characteristics across the globe. For the Greater Yellowstone Ecosystem (GYE), under future warming temperatures, wildfire activity is expected to increase and the suitable habitat for many dominant tree species is expected to shrink. Previous studies predict large high severity fires to occur more frequently, potentially so frequent that forests are unable to grow old enough to produce seeds and self-regenerate. Studies of suitable climate spaces show that previously habitable areas may become too warm or dry to support common GYE trees. The first goal of this dissertation was to use vegetation images from satellites to detect recent changes in forest productivity in the GYE, and then determine the relative importance of recent climate and disturbance observations in explaining these changes. We found that areas with detected increases in plant growth, or 'greening' trends, were associated with forested areas regenerating after wildfire. Detected decreases in plant growth, or 'browning' trends, were associated with areas that had recently burned. Historically dry areas with recent increases in precipitation were associated with greening trends. Warming of 0-2 °C was associated with greening trends, while greater increases in temperature (>2 °C) were correlated with browning trends. The key take-away is although forests in the GYE are usually considered temperature limited, changes in precipitation may be more important than previously thought. The second goal of this dissertation was to adapt a global vegetation computer model for regional applications to simulate forests and wildfire dynamics, ultimately to run simulations under future climate conditions to predict how forest extent and composition may change. Life history characteristics and climate limitations were aquired for the dominant GYE plant types to dictate their establishment, growth, competition, and mortality in the new model. Before running future simulations, it is required to evaluate how well the model represents current conditions. Adding new equations that calculate the initiation, spread, and effects of crown fires was required to reproduce recent vegetation abundance, distribution of plant types, and fire activity in the GYE. Methods, expected results, and implications of running future simulations are described in Chapter 4.Item Effects of coalbed natural gas development on fish assemblages in tributary streams in the Powder River Basin, Montana and Wyoming(Montana State University - Bozeman, College of Letters & Science, 2008) Davis, Windy Niccole; Chairperson, Graduate Committee: Alexander V. Zale; Robert G. Bramblett (co-chair)The Powder River Basin in Wyoming and Montana is undergoing the world's largest development of coalbed natural gas (CBNG) extraction. Potential exists for substantial effects on aquatic ecosystems because CBNG development involves production and disposal of large quantities of CBNG product water that differs from surface waters and alters natural flow regimes. In 2005 and 2006, I compared fish assemblages in streams with (treatment) and without (control) CBNG development, determined fish presence, growth, and survival in streams composed entirely of product water, and compared fish assemblages at multiple points above and below development to determine the effects of coalbed natural gas development on fish assemblages in the Powder River Basin. Some evidence suggested CBNG development had little or no effect on fish. For example, species richness and index of biotic integrity (IBI) scores were similar between developed and undeveloped sites, and no strong relationships existed between overall IBI scores or most IBI metric scores and the number or density of CBNG wells in a drainage area. Streams composed largely or entirely of product water were inhabited by reproducing populations of several species of fish. Other evidence suggested that CBNG may negatively affect fish assemblages over time. Conductivity was on average higher in treatment streams and was negatively related to biotic integrity. Bicarbonate, one of the primary salts in product water, appeared to be harmful to some species of fish. One salt-tolerant non-native species, northern plains killifish, was observed almost exclusively in treatment streams. The study was limited by a lack of pre-development data, unquantifiable product-water discharges, and because it was conducted during dry years. Potential effects of CBNG development may be more apparent during wet years when more sensitive fish assemblages are present. Monitoring efforts, development of a bicarbonate water quality standard, and efforts towards requiring complete product-water discharge reporting should continue.