Browsing by Subject "spatial modeling"

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    The Epidemiology of Civil War
    (2022-07) Stundal, Logan
    This dissertation explores the causal connection between violence occurring in armed conflicts and the emergence of infectious disease within or in close proximity to active conflict zones. While we have known for quite some time that war leads to disease, our understanding of what types of violence contribute to higher (or lower) incidence of specific types of infectious disease remains limited. Establishing the connection between disease and patterns of violence in armed conflict is important since that knowledge can help to inform where humanitarian aid should go and, crucially, what form that aid should take to best support the health needs of civilians suffering the effects of violence. I propose a new theory explaining the disease-conflict connection through a mechanism of civilian population movements in response to changing patterns of observable violence occurring across varying conflict contexts. Variation in conflict intensity as well as the spatial location of that violence – conflict geography – helps to explain downstream variation in the spread of infectious disease. This theory relies upon a mechanism of rational civilians making decisions to maximize their safety in response to violence. As security conditions deteriorate, civilians attempt to improve their situation by pursuing a strategy to remove themselves from areas which present the greatest risk to their personal integrity. In order to decide how to respond to the violence they observe, civilians jointly examine the intensity and geographic location of violence and decide whether to shelter in place, shuffle into nearby areas to find safety, or flee longer distances into neighboring regions or countries. My dissertation demonstrates that conflict context shapes how civilians respond to changing levels of violence. The varied strategies civilians pursue in response to this violence influences the spread of infectious disease by shaping which disease-causing pathogens civilians are more or less likely to encounter. Some patterns of violence facilitate contagious disease transmission while others create ideal conditions for noncontagious disease infections. By explaining the connection between conflict and war through civilian displacement mechanisms, the theory presented and tested in this dissertation allows us to better understand why disease emerges in some conflicts but not others, but also where and what types of disease will emerge across different conflict contexts.
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    Evaluating how spatial heterogeneity in forage chemistry and abundance influences diet and demographics in a declining moose (Alces alces) population in northeast Minnesota.
    (2019-05) Berini, John
    Since 2006, the moose population in northeastern Minnesota has declined by nearly 50%. While recent warming has been implicated as a primary cause of this decline, there is little evidence to support this relationship. More recent evidence suggests that the influences of warming and poor nutrition may predispose moose to increased risk of mortality, including mortality attributed to predation and disease. During summer, moose begin to experience the detrimental effects of high temperatures at around 14 to 17 ºC, and mean-maximum summer temperatures in this area range from 19.5 ºC along Lake Superior, to approximately 24.5 ºC in the more central part of the region. Thus, moose in northeastern Minnesota are likely dealing with the negative effects of high temperatures on a routine basis throughout summer. While it has been suggested that nutrition and warming may be acting in concert to influence moose demographics in Minnesota, potential synergisms between these factors have not been investigated. Thus, I evaluated how spatial variation in the thermal landscape influences forage chemistry, the abundance and distribution of forage, and the spatial variation in moose diets and overwinter survival. To determine how high temperatures might influence the chemistry of moose forage, I used untargeted metabolomics to evaluate how varying combinations of temperature, moisture, and light in both experimental and natural conditions influence the production of plant secondary metabolites in moose forage. To investigate how the abundance and chemistry of moose forage varies across NEMN, I used a mixed-effects regression kriging framework to estimate spatial variation of δ13C and δ15N values in plants commonly eaten by moose, and then refined these predictions using species-specific allometric equations to estimate above-ground biomass of moose forage. Finally, to investigate the interaction between spatial variation in high summer temperatures, moose diet, and over-winter survival, I used stable isotope values from forage and hair to estimate moose diet via Bayesian mixing models, and then evaluated if diet composition and quality vary as a function of mean-maximum summer temperature, season, or winter mortality. In general, warming and high-temperatures had variable effects on the defensive chemistry of moose forage, only a minor influence on forage abundance, and a strong effect on diet quality, composition, and overwinter survival. Specifically, when investigating the influences of warming on PSM production in moose forage, I found that the influences of temperature can be modulated by the presence or absence of other abiotic factors, such as precipitation and light. As an example, the relative abundance of compounds known to negatively influence moose herbivory increased by 250% or more when high temperatures occurred in an open canopy setting. When modeling spatial heterogeneity in the chemistry and abundance of moose forage across northeastern Minnesota, I found that while mean-maximum summer temperature played a strong role in the isotopic composition of moose forage across the region, it had only a minor effect on distribution and abundance. Finally, when investigating interactions between spatial variation in high summer temperatures, moose diet, and over-winter survival, I found that the warmest parts of the moose range in Minnesota were those where moose diets were poorest and where winter mortality rates were highest. Specifically, I found that moose in the warmest parts of the range have diets containing the highest proportion of aquatic forage and the lowest proportion of high-preference forage. Additionally, moose that did not survive winter had diets containing substantially greater proportions of aquatic forage throughout the entire growing season when compared to moose that survived, which consumed mostly high-preference forage during early summer but increased their consumption of aquatics during late summer. Finally, while I estimated overall mortality to be at approximately 30% throughout the entire study region, mortality in the warmest parts of the range (69%) was approximately 4.5 times higher than that in the coolest parts of the range (15%). Given the evidence I present here, habitat-improvement projects may want to focus on promoting the regeneration of forage species that can adapt to future warming scenarios, while still providing thermal refuge, and proper nutrition during late summer. Also, future studies should evaluate spatially explicit differences in habitat use as a function of the thermal landscape and how variation in habitat use-behavior (i.e., movement) within the thermal landscape may influence diet composition, quality, and nutritional restriction. Identifying mechanistic links between movement, diet, and nutritional condition within the thermal landscape would advance our basic knowledge of large mammal behavior and ecology, as well as help develop sound management strategies in how we plan for future warming.