Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
Browse
2 results
Search Results
Item Emergence of cooperative behavior in microbial consortia(Montana State University - Bozeman, College of Letters & Science, 2018) Schepens, Diana Ruth; Chairperson, Graduate Committee: Tomas GedeonCooperative microbial communities and their impact are ubiquitous in nature. The complexities of the cross-feeding interactions within such communities invite the application of mathematical models as a tool which can be used to investigate key influences in the emergence of cooperative behavior and increased productivity of the community. In this work, we develop and investigate a differential equation model of competition within a chemostat between four microbial strains utilizing a substrate to produce two necessary metabolites. The population of our chemostat includes a wild type strain that generalizes in producing both metabolites, two cross-feeding cooperator strains that each specialize in producing one of the two metabolites, and a cheater strain that produces neither metabolite. Using numerical methods we consider three key characteristics of the microorganisms and investigate the impact on the emergence of mutual cross-feeding in the community. First, we investigate the impact that substrate input concentration and the rate and type (active vs. passive) of metabolite transport between cells has on the emergence of cooperation and multi-stabilities resulting from the competition. Second, we investigate the role that resource allocation within metabolic pathways plays in the results of the competition between cells with different metabolite production strategies. Introducing metabolite production cost into the model leads to new outcomes of the competition, including stable coexistence between different strains. Lastly, we examine the effect that an initial population of a non-cooperative cheater strain has on the outcome of competition. Our results show that the emergence of a cross-feeding consortia relies on the availability and efficient use of resources, ease of transport of metabolites between cells, and limited existence of cheaters.Item Interaction turnover among pollination networks across space, time, and environment(Montana State University - Bozeman, College of Letters & Science, 2013) Simanonok, Michael Peter; Chairperson, Graduate Committee: Laura BurklePollination networks provide an ideal system in which to test hypotheses around interaction turnover across ecologically meaningful gradients, as there is already baseline understanding of plant and pollinator communities. Parallel declines in plants and pollinators imply that disruption of interactions between species in pollination networks may be leading to pollinator declines; therefore, beginning to understand how plant-pollinator interactions turnover through space, time, and environment could be vital for future conservation and management efforts. I investigated i.) how do plant and pollinator species diversity (i.e., richness and evenness), phenology, and composition change across space, time, and environment, ii.) how do interactions between pollination networks turn over across these same gradients (i.e., space, time, and environment), and iii.) what is the relative contribution of species turnover (plant, pollinator, or both simultaneously) vs. host switching to interaction turnover among pollination networks? Field work was conducted during summer 2012 on the Beartooth Plateau, an alpine ecosystem in Montana and Wyoming, with weekly observations of plant-pollinator interactions and the floral community across the growing season. Community diversity and composition were compared across space, time, elevation, slope, and aspect using linear regressions, t-tests, and principle coordinate analysis. Interaction turnover was calculated between all possible pair wise combinations of study site and week and compared across, space, time, elevation, slope, and aspect using a partial Mantel test and linear regressions. We found that interaction turnover mostly occurred due to simultaneous species turnover of both plant and pollinator communities with host-switching having marginal contribution. Furthermore, interaction turnover occurred across temporal and environmental gradients, with no significant variation across spatial scales. These results differ greatly from inter-annual patterns on the contribution of species turnover vs. host switching, however some results may be due to sampling or scale limitations. It is possible that host switching does not readily occur within-season, but more work is needed for confirmation. Spatial and environmental patterns remain possible, but did not emerge at the extents used herein. This study represents the first instance of the partitioning of interaction turnover into individual species components for a pollination network, and the first to do so intra-annually.