Bison-mediated seed dispersal may be a critical ecological process that has been eliminated in grassland ecosystems by the removal of this keystone species. In this study of epizoochory and endozoochory by bison, we installed funnel seed traps on 50, 50-m transects on the Neal Smith National Wildlife Refuge in south central Iowa, to compare the composition and density of seed species dispersed by bison with the abiotic seed rain in a tallgrass prairie reconstruction. Seed trap, dung, and shed hair samples were collected monthly from April 2011 through November 2013. Hair samples were clipped directly from bison at the end of the plant growing season during annual November round-ups. Seeds were identified and classified as native or non-native, by plant functional group, and by diaspore characteristics. A diverse mix of epizoochorus seeds, wind dispersed propagules, and seeds with smooth, rounded diaspores in bison dung, shed hair, and attached to the animals, suggests that bison are generalist dispersers of both forbs and graminoids. Bison dung contained seeds in similar proportions to those collected in seed traps. Shed bison hair contained a significantly greater

proportion of both native species and grass seeds than were found in bison dung or seed trap samples. Seed compositions in shed hair and dung appeared to be influenced by the phenology of seed production, the foraging behavior of bison, and the movements of bison through a variety of vegetation types. Bison are the dominant grazers in many large public and private grasslands of western North America. Conservation herds are growing and are being reintroduced to both newly reconstructed prairies and remnant prairies that have been without this keystone species for over a century. Our study provides needed information concerning the potential for bison to act as seed dispersal agents in these often fragmented ecosystems.