Theses and Dissertations at Montana State University (MSU)
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Item Development of a total systems approach to multi-pest management decision analysis(Montana State University - Bozeman, College of Letters & Science, 2012) Keren, Ilai Naftaly; Co-chairpersons, Graduate Committee: James Robison-Cox and Fabian D. MenalledThe concentration of wheat production in the Northern Great Plains has resulted in the development of specialized multitrophic agricultural pest complexes whose members interact in both positive and negative ways. In this context, management recommendations based on the traditional single-species pest control paradigm may lead to undesirable outcomes. Our goal was to develop a modeling framework to make multi-pest management decisions that take into account the existence of direct and indirect interactions among pests. We a Bayesian decision theory approach in combination with a analysis where observed intermediate nodes were replaced with error terms. This model holds several advantages current decision models, in particular it allows intuitive of coefficient estimates as the total, direct and through pest interactions, impact of management on the. We evaluated interactions between Bromus tectorum), Fusarium crown rot, and Cephus cinctus (wheat stem sawfly) as well as assessed the joint response of these pests to wheat seeding rates, cultivar competitiveness, and cultivar stem sawfly tolerance. Results indicate that yield differences be more readily explained as a result of the effects of on pests and multi-pest interactions, rather than just by direct effect of any particular management scheme on yield. Our provides a framework for finding the balance between simplicity and the complexity of the process being modeled, also bridges the gap between making inferences from experimental observational studies and ecological management decisions.Item Thermal balance model for cattle grazing winter range(Montana State University - Bozeman, College of Agriculture, 2005) Keren, Ilai Naftaly; Chairperson, Graduate Committee: Bret E. Olson.Beef cattle grazing semi-arid foothill range of the Northern Rockies during winter may be exposed to cold temperatures and high winds while grazing pastures with low nutritional value. Cattle can physiologically and behaviorally respond to the changing environment to lower metabolic requirements and reduce the effects of cold exposure. Requirements of grazing cattle may be overpredicted with models developed in controlled settings that do not account for energy conserving behaviors. We refined a simple thermal balance equation to model heat exchange of free-ranging cattle. We accounted for the complex interactions between animal behavior and the changing natural environment by applying the insulation characteristics of cattle's tissue and coat to, first, a simple geometric shape of an asymmetric ellipsoid, and second, to a three-dimensional computer model of a cow at different orientations to the sun and wind. A group of mature cows grazing native range were observed from dawn to dusk from 28 November 2003 to 21 January 2004. These observations were used to evaluate our model and as reference for analyzing cattle behavior in response to environmental variables. Correlation (r) between predicted and measured surface temperatures was 0.82, indicating the model successfully quantifies heat exchanges of cattle exposed to cold conditions in the field. We compared our model predictions with heat production measured in three studies, and with predictions based on the National Research Council beef cattle model. In all cases our model predictions were similar to those reported. Model simulations indicate behavior such as lying and orientation to the sun helped mitigate the effects of extreme weather, and that for many combinations of winter weather variables there is only a small increase in metabolic requirements due to cold exposure in mature beef cattle in a maintenance state. Our results indicate solar radiation contributes strongly to a cow's thermal balance. Thus, previous estimates that did not account for the irradiative environment may have overestimated metabolic requirements of acclimated cattle grazing winter range.