American bison are the largest mammal to have survived the last glacial period in North America and are a critical keystone species in grassland ecosystems. While more than 500,000 bison exist today, they are nearly all derived from a handful of publicly-managed herds in the U.S. and Canada which represent the genetic “stock” of the bison species. One of these significantly important herds is maintained at Badlands National Park (BNP), which was first established in 1963 with bison originally from Nebraska (Fort Niobrara National Wildlife Refuge lineage) and later supplemented in 1983 with bison from Colorado. Genetic data were collected over a period of 5 years to investigate the levels and patterns of variation within the herd in order to assist with long-term management goals and priorities. Without question, genetic variation is important for long-term population health (viability), and BNP bison have moderately high levels of genetic variation compared with other U.S. federal herds. Like most of the US federal system bison herds, extremely low levels of domestic cattle DNA (introgression) exist in BNP bison.
Interestingly, two different genetically defined “subpopulations” were discovered in the BNP herd, corresponding to the two historical lineages represented in this herd (Nebraska & Colorado). The observation that bison in this herd preferentially associate with others from their original founding lineage 25 years after the lineages were “mixed” was an unexpected finding by scientists and population managers. In fact, this new discovery could have significant implications for the future management of this national resource and may require more detailed evaluations of hidden population structure and management policies with other important federal bison herds.
Computer simulations were also performed to test the effects of intensive culling, which has been proposed to reduce the herd size from around 850 to 600 bison. While culling duration (years) and intensity are predicted to have only a minimal impact on short-term (less than 10 years) genetic diversity, over longer time periods (100 years) total population size is expected to have a significant impact on genetic diversity. In fact, to maximize levels of genetic diversity in the BNP herd, the results of this study indicate that the herd should be maintained with at least 800-1000 bison. This study underscores the value of using modern biotechnology to help ensure the preservation and conservation of the BNP bison herd for generations to come and could provide valuable insight for future species conservation endeavors.
This work was funded through the National Park Service Great Plains Cooperative Ecosystems Study Unit.