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Item Irrigation ditches as novel intermittent stream networks that provide energetic subsidies to terrestrial ecosystems via aquatic insect emergence(Montana State University - Bozeman, College of Letters & Science, 2024) Heili, Nathaniel Maxwell; Chairperson, Graduate Committee: Wyatt F. CrossNon-perennial streams dominate fluvial networks, comprising over half of lotic ecosystems globally. Although little attention has been paid to these systems relative to those that are perennial, perhaps even less is known about the ecology of artificial intermittent streams. In irrigated river valleys, ditches comprise a substantial proportion of surface water networks, but little is known about their relative contributions to lotic habitat, freshwater biodiversity, and ecosystem processes. Because ditches are abundant and permeate arid floodplains, they create new opportunities for cross-ecosystem subsidies through emergence of adult aquatic insects. Here, we mapped the extent of an irrigation ditch network relative to natural surface waters in the Gallatin River Valley, Montana, USA. We also quantified the magnitude, composition, and phenology of aquatic insect emergence in ditches throughout a full irrigation season and compare emergence to nearby natural streams in the valley. We found that non-perennial streams, both natural and artificial, dominated the surface-water network, representing over 70% of total length. Irrigation ditches also constituted 37% and 23% of total length and surface area of all waterbodies in the valley, respectively. Insect emergence production from ditches averaged 32.0 mg m -2 d -1 and exceeded fluxes from nearby natural streams, which contained more classically sensitive taxa (i.e., Ephemeroptera, Trichoptera, and Plecoptera). Ditches varied in water temperature, substrate size, and flow permanence, leading to distinct emergence timing, species composition, and magnitudes of biomass flux. One of the study ditches dried early because of more 'junior' water rights, but this ditch provided the largest emergence subsidy, including a pulse of dipteran emergence at the onset of flow cessation. Annual production from intermittent ditches was ~6 g m -2 y -1 and was comparable to estimates from natural perennial streams. Although our study focused on one river valley of the western US, results suggest that these ecosystems contribute broadly to lotic habitat, heterogeneity, and cross-ecosystem subsidies via aquatic insect emergence. Given increasing demand for water and changes to flow regimes and water management driven by climate change, additional study is needed on these novel and underappreciated artificial ecosystems.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 Environmental drivers of salmonfly ecology in southwest Montana(Montana State University - Bozeman, College of Letters & Science, 2018) Anderson, Heidi Elise; Chairperson, Graduate Committee: Lindsey Albertson; Lindsey K. Albertson and David M. Walters were co-authors of the article, 'Temperature-driven range contraction and body size reduction of an iconic aquatic insect' submitted to the journal 'Freshwater science' which is contained within this thesis.; Lindsey K. Albertson and David M. Walters were co-authors of the article, 'Landscape features drive synchronicity of an aquatic insect resource pulse' submitted to the journal 'Ecological applications' which is contained within this thesis.Aquatic insects have ecological, cultural, and economic value throughout the American West. They can control the processing of in-stream nutrients, are a vital component of both aquatic and terrestrial food webs, and support economically important species such as trout and the eco-tourism industries structured around these fisheries. Salmonflies (Pteronarcys californica) are one of the most well-known aquatic insects in the American West due to their large size and popularity among fly-fishers. However, mounting anecdotal evidence suggests that salmonfly populations could be in decline. We conducted surveys and compiled historical datasets that quantified salmonfly abundance, body size, and emergence timing along the Gallatin and Madison Rivers in southwest Montana to determine the status of salmonfly populations in these rivers, understand environmental drivers that are constraining their distribution and driving their development, and initiate long-term monitoring. Most notably, we found evidence for temperature-driven changes in salmonfly distribution and body size along the Madison River in the last four decades and observed marked differences in salmonfly emergence phenology and duration at multiple spatial scales between the Madison and Gallatin Rivers. Above-optimal summer water temperatures appear to be the major constraint on salmonfly populations in the Madison River, but only play a minimal role in dictating salmonfly distribution along the Gallatin River. This research provides rare empirical evidence of long-term biological change of an aquatic insect and highlights the importance of combining temporal and spatial datasets to explicitly address species' responses to environmental stressors across multiple spatial and temporal scales. Freshwater habitats are increasingly imperiled by climate change and human-induced habitat alteration, which will invariably continue to impact the ecology of aquatic insects like salmonflies. This work contributes to the understanding of how these ongoing changes will influence the structure of aquatic communities, the flow and transfer of energy and nutrients, consumer-resource dynamics, and stream--riparian food web linkages.Item Ecology of aquatic insects in the Gallatin River drainage(Montana State University - Bozeman, College of Letters & Science, 1990) Gustafson, Daniel L.; Chairperson, Graduate Committee: Daniel Goodman; George R. Roemhild (co-chair)Item The effects of iron on the macroinvertebrates of Soda Butte Creek(Montana State University - Bozeman, College of Letters & Science, 1974) Chadwick, James WoodrowItem The distribution and abundance of aquatic insects in the middle West Gallatin drainage(Montana State University - Bozeman, College of Agriculture, 1973) Garrett, Paul AllenItem The effects of heavy metals on the distribution and abundance of aquatic insects in the Boulder River, Montana(Montana State University - Bozeman, College of Letters & Science, 1977) Gardner, William M.Item A comparison of riffle insect populations in the Gibbon River above and below the geyser basins, Yellowstone National Park(Montana State University - Bozeman, College of Letters & Science, 1966) Vincent, E. RichardItem The responses of insect communities in the East Gallatin River, Montana, to sewage effluents(Montana State University - Bozeman, College of Agriculture, 1972) Glorvigen, Thomas HarveyItem Effects of controlled flow reductions on aquatic insects in a stream riffle(Montana State University - Bozeman, College of Letters & Science, 1968) McClay, William