Genetic Management

Developing Genetic Management Strategies to Ensure the Long-Term Conservation of Plains Bison across North America

PROJECT TYPE: Scientific research, Conservation genetics, Partnership building for conservation

PARTNERS: U. S. Department of the Interior, U. S. National Park Service, U. S. Fish and Wildlife Service, Bureau of Land Management, Utah State Parks, Texas State Parks, Parks Canada

VISION: Using genetics to build a common framework for the conservation and management of bison across North America

MOTTO: Bison bison

In the early 1900s the dedicated efforts of individuals and private organizations prevented the imminent extinction of bison and allowed population numbers to rebound. Today, there are an estimated 20,000 plains bison in conservation herds managed by Tribes, non-profits, and government agencies across North America. Over 200,000 bison are found on private ranches across North America, also meaningfully contributing to the conservation of the species.

While plains bison are no longer in danger of imminent extinction, concerns have been raised about their long-term ecological viability. Most conservation bison herds today contain fewer than 500 individuals, are constrained by fences, and are culled to maintain low population densities. Most herds have also been managed as independent populations, with little to no natural movement of individuals between herds. Small, isolated herds are more vulnerable to extinction than large herds, and lose genetic diversity faster through a process called genetic drift. Loss of genetic diversity can increase the risk of inbreeding depression in a herd (a reduction in reproduction and survival in the offspring of closely related parents), and reduces the ability of herds to adapt to changing environmental conditions, such as increased climatic variability or the emergence of novel diseases.

In response to these concerns, the Wildlife Conservation Society partnered with the U.S. National Park Service to evaluate the long-term population and genetic viability of 18 bison herds on federal lands, and to develop scientific guiding principles to support the long-term conservation of bison. Specific aims of the project included:

  • Collecting and analyzing standardized genetic data from individual herds to evaluate current levels of genetic diversity within herds and genetic relationships between herds;
  • Developing population models to project how current management conditions (with little to no movement of animals between herds) affect the genetic diversity of bison herds over time;
  • Using population models to forecast how alternative management scenarios, including the movement of animals between herds, might affect the genetic diversity of bison over time.

Our results indicated that all 18 herds were projected to lose genetic diversity over time if managed in isolation. Herd size was the primary driver of diversity loss across all herds, though harvest/culling strategies and initial levels of genetic diversity also affected levels of diversity loss within individual herds. Modeling alternative management scenarios confirmed that increasing herd size and periodically translocating animals between genetically unrelated herds were the most effective methods for conserving genetic diversity for all herds.

This project provides an ideal framework for developing a science-based, continent-wide bison management strategy and has been influential in shaping the U.S. Bison Conservation Initiative. Herds on U.S. federal lands account for approximately half of all plains bison in conservation herds in North America. Expanding our modelling framework to include additional conservation herds from throughout the U.S., Canada, and Mexico will enable the development of collaborative partnerships across jurisdictions to increase the genetic health of individual herds, ensure the long-term viability of plains bison as a whole, and establish a foundation for the ecological and cultural restoration of bison across the continent.

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