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          DIET, GUT MICROBIOTA, AND MANAGEMENT OF AMERICAN BISON (Bison bison) IN 
                CONSERVATION AND COMMERCIAL HERDS OF THE GREAT PLAINS 
                                        by 
                             GADDY THEODORE BERGMANN 
                          B.A., University of Colorado, Boulder, 1996 
                            M.S., University of South Florida, 2002 
                                          
                                          
                                 A thesis submitted to the 
                             Faculty of the Graduate School of the 
                           University of Colorado in partial fulfillment 
                             of the requirement for the degree of 
                                  Doctor of Philosophy 
                         Department of Ecology and Evolutionary Biology 
                                       2016 
                                                            
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                            This thesis entitled: 
          Diet, gut microbiota, and management of American bison (Bison bison) in conservation and 
                        commercial herds of the Great Plains 
             has been approved for the Department of Ecology and Evolutionary Biology 
                                  
                    ________________________________________ 
                            Noah Fierer, PhD 
                                  
                    ________________________________________ 
                           Valerie McKenzie, PhD 
                                  
                                            Date _________________ 
              The final copy of this thesis has been examined by the signatories, and we 
             find that both the content and the form meet acceptable presentation standards 
                    of scholarly work in the above mentioned discipline. 
                                                 
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          Bergmann, Gaddy Bergmann (Ph.D., Ecology and Evolutionary Biology) 
          Diet, gut microbiota, and management of American bison (Bison bison) in conservation and 
          commercial herds of the Great Plains 
          Thesis directed by Associate Professor Noah Fierer 
           
          ABSTRACT 
               Because American bison (Bison bison) are important to both conservation and ranching, I 
          inquired as to the diet and gut microbiota of these animals, and the implications of these factors 
          for sound management. I found that bison in Kansas browsed more in spring and fall, and 
          consumed more forbs during summer, but graminoids formed a consistently low proportion of 
          the diet. In Colorado, the bison diet was dominated by graminoids, followed by forbs, then 
          browse. This pattern remained consistent for 18 months, despite a brief increase in forbs and 
          decrease in graminoids when the herd’s pasture was enlarged. Comparisons among sites from 
          May-August showed significant differences, with bison in Montana and Kansas consuming more 
          forbs and browse than those in Colorado during certain months. Thus, the diet of bison was 
          temporospatially variable and sometimes deviated significantly from grazing, possibly due to 1) 
          plants that are high in protein and low in toxins; 2) large body size dictating less forage 
          selectivity; 3) a lack migration; and 4) broad niche breadth. The present study suggests that bison 
          may benefit from access to forbs and browse in addition to grasses. I also compared gut 
          microbiota along the digestive tract between grass-finished and grain-finished bison. Location 
          had the greatest effect, with sections of the foregut, the hindgut, and to a lesser degree the midgut 
          being statistically similar. I also found a significant effect of diet on gut microbiota throughout 
          the digestive tract, with the grain-finished bison exhibiting higher relative abundances of the 
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        bacterial phyla Firmicutes and Proteobacteria. Finally, my analysis of the natural and human 
        history of the Great Plains shows that bison and other animals, as well as new energy sources, 
        have the potential to foster both ecological and economic sustainability in the region to a greater 
        degree than the system currently in place.