Long-term viability of Department of the Interior bison under current management and potential metapopulation management strategies

Hartway, Cynthia; Hardy, Amanda; Jones, Lee; Moynahan, Brendan; Traylor-Holzer, Kathy; McCann, Blake; Aune, Keith; Plumb, Glenn

The North American plains bison (Bison bison bison) once numbered in the tens of millions, with a range that extended from northern Mexico to central Canada. Yet by the end of the 1800s, a combination of commercial hunting, novel diseases, and habitat destruction had driven plains bison to the brink of extinction. The establishment of a small number of protected, federally managed herds in the early 1900s saved the subspecies from extinction in the wild. As a result of those efforts, the Department of the Interior (DOI) is now the primary national conservation steward of North American plains bison supporting approximately 11,000 plains bi-son in 19 herds on 4.6 million acres of National Park Service (NPS), US Fish and Wildlife Service (FWS), and Bureau of Land Management (BLM) lands in 12 states. While plains bison are no longer threatened by demographic extinction, most DOI bison continue to exist in relatively small, isolated, range-restricted herds, confined by fences and further bound by socio-political concerns that limit their ecological recovery. Small, isolated populations are vulnerable to extirpation due to random catastrophic events such as disease outbreaks or extreme weather events. Small, isolated populations also lose genetic diversity more quickly than large populations through the process of genetic drift, which in turn can decrease the viability of populations through an accumulation of inbreeding and loss of adaptive capacity. To mitigate the loss of genetic diversity in these isolated populations, previous researchers have suggested restoring effective gene flow among herds and managing DOI bison herds as a metapopulation. Gene flow can be restored either through the restoration of natural movements between populations or through the translocation of animals (or gametes) among populations. In this project, the NPS partnered with the Wildlife Conser-vation Society (WCS) and the FWS to evaluate the ability of metapopulation management strategies to ensure the long-term population viability of DOI bison. This study had three major components: In collaboration with other stakeholders including the BLM, state wildlife managers, non-government orga-nizations, and Canadian bison managers, we collected standardized, up-to-date genetic, demographic, and management data on 16 DOI and two Parks Canada herds (collectively simplified and referred to as DOI bison herein), to assess current existing genetic variation within and between herds (Chapter 2); We used these genetic, demographic, and management data to develop and parameterize individual-based, genetically explicit simulation models to project the long-term viability of each bison herd under current management practices (Chapter 3); We used this model to evaluate the effects of alternate metapopulation management strategies with varying levels of genetic exchange (translocations) between herds to ensure the long-term viability of DOI bison (Chapter 4). To evaluate and compare the performance of the alternate bison management strategies modeled in this study, project partners established the following quantitative criteria for successful management: All DOI bison herds must have a 99% probability of sur-viving and maintaining currently established abundance objectives for 200 years; The existing genetic diversity within each individual bison herd must be maintained or improved; Existing genetic diversity within the DOI metapopula-tion as a whole must be maintained; and Genetic redundancy should be retained within the DOI metapopulation, such that the loss of any one DOI bison herd does not substantially reduce the genetic diversity of DOI herds as a whole. Results from our genetic analyses (Chapter 2) identify con-siderable variation in the level of genetic diversity within, and significant genetic differentiation between, existing bison herds. Current levels of genetic diversity within herds gener-ally correspond with known herd foundation...

Long-term viability of Department of the Interior bison under current management and potential metapopulation management strategies

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