Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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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 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.