Date of Award

Spring 1-1-2016

Document Type


Degree Name

Doctor of Philosophy (PhD)


Ecology & Evolutionary Biology

First Advisor

Noah Fierer

Second Advisor

Valerie McKenzie

Third Advisor

Timothy Seastedt

Fourth Advisor

Steven K. Schmidt

Fifth Advisor

Joseph M. Craine


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 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.