Bison-mediated seed dispersal in a tallgrass prairie reconstruction

Background/Question/Methods

Animal-mediated seed dispersal may be a critical ecological process, eliminated by the removal of key animal species from ecosystems. Due to grazing activities, bison have been considered keystone species in the evolution of tallgrass prairies, but bison also have great potential to be effective seed dispersers. This study was initiated to determine the degree to which bison play a role as dispersal agents in tallgrass prairie ecosystems. As part of a larger study, we addressed the role of bison in native and non-native seed dispersal via shed hair in initial stages of a tallgrass prairie reconstruction. In this poster we report the seed composition in shed bison hair, as well as hair clipped from the bison at the end of the growing season. We hypothesized that seed species composition would differ by season of adherence, by age-sex class of bison, and location on the body. Thirty five samples of shed bison hair were collected in May through July 2007. We clipped bison hair samples from the head and/or body of 8 bulls, 10 cows and 29 juveniles in November of 2010. Seeds were identified to species or genus, classified as native or non-native ,by size, and by diaspore characteristics.

Results/Conclusions

Shed bison hair contained significantly more  native species than non-native species. Preliminary results suggest a higher percentage of forbs in hair samples clipped from the bison in fall compared to hair shed naturally in summer.  Seed species composition differed in hair samples collected from calves, yearlings, cows, and bulls, based on preliminary evidence.  In addition, the ratio of grass to forb seeds appeared to differ in samples clipped from the head and body. Numerous species found in bison hair showed specialized appendages for wind dispersal rather that adhesive dispersal. Differences in dispersal of native versus non native species in shed hair may be due to habitat selection, diet, or composition of plant communities in the ongoing reconstruction. A diverse mix of native and non-native seeds were found in shed bison hair and attached to the animals, suggesting that bison are potential dispersers of both forbs and grasses.