Scholarship & Research
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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 The use of aquatic macroinvertebrates as water quality indicators in mountain streams in Montana(Montana State University - Bozeman, College of Agriculture, 1996) Richards, David C.Item Grasshopper hemagglutinin : immunochemical localization in hemocytes and confirmation of non-opsonic properties(Montana State University - Bozeman, College of Letters & Science, 1987) Bradley, Roger StevenItem The population dynamics and production of the net zooplankton in Georgetown Lake, Montana in 1974(Montana State University - Bozeman, College of Agriculture, 1977) Geer, William HerbertItem Benthic invertebrate distribution, abundance, and diversity in Rosebud Creek, Montana(Montana State University - Bozeman, College of Agriculture, 1977) Baril, Steven F.Item Observations of distribution, abundance and production related aspects of aquatic macro-invertebrates in natural thermal gradients(Montana State University - Bozeman, College of Agriculture, 1979) Oswald, Richard AllenItem Characterization of the neural codebook in an invertebrate sensory system(Montana State University - Bozeman, College of Letters & Science, 2007) Aldworth, Zane Nathan; Chairperson, Graduate Committee: John P. Miller; Tomas Gedeon (co-chair)An outstanding problem in neuroscience is to describe the relationship between various stimulus sources in the environment and how they are represented by patterns of activity in nervous systems, a problem generically referred to as 'neural coding'. Most previous methods developed to address this problem have assumed a linear relationship between environmental stimuli and neural responses, and generally relied on measures of the mean state of the environment preceding neural activity to characterize the stimulus-response transformation. The goal of this thesis is to develop new methods of characterization that extend earlier work, and to demonstrate the utility of these new methods through application to an invertebrate sensory system. All applications of the methods developed in this thesis were carried out in the cercal system of crickets. The cercal system mediates the detection and analysis of low velocity air currents, and is implemented around an internal representation of air current direction that demonstrates the essential features of a continuous neural map. The stimulus feature selectivity, timing precision and coding characteristics of two bilateral pairs of primary sensory interneurons of the cercal system were characterized using three novel techniques. First, estimates of the cells' feature selectivity that take the natural variance in stimulus-response latency (i.e., spike 'jitter') into account were derived. Second, the cells' stimulusresponse relationship was probed for specific non-linear aspects that could constitute 'temporal' encoding. Third, an iterative stimulation paradigm was used to test and refine the predictions of the cercal system's stimulus selectivity. Compared to earlier characterization of this system, these new analytical procedures yield significantly different estimates of the stimulus feature selectivity of these cells. A 'code book' for the stimulus-response characteristics of these cells is presented, with emphasis on demonstrating instances where a cell represents different stimuli with distinct spike 'code-word' patterns.