American Bison - IUCN

that “Further research and debate by taxonomists, and the bison
conservation community, is required to reconcile molecular,
behavioural and morphological evidence before a change in
nomenclature could be supported, and thus, for this document,
the American Bison Specialist Group adheres to the genus Bison
with two species, B. bonasus and B. bison. Not surprisingly,
disagreement also exists regarding the subspecies status of
wood and plains bison. However, Boyd et al. emphasise that this
debate does not negate the importance of conserving the two
forms as separate entities. From a conservation perspective, the
goal is to conserve “evolutionarily significant units” or “distinct
population segments,” among other terms used to define
geographic variation among populations, a concept recognised
by both the U.S. Endangered Species Act and the Committee
on the Status of Endangered Wildlife in Canada. Keeping wood
bison and plains bison as separate non-interbreeding units is the
recommended precaution.
Genetics play a particularly complex and important role in
bison conservation, as explained by D. Boyd and co-authors
in Chapter 4. The rapidly advancing science of genetics has
recently brought new information and insights into not just
the evolutionary relationships among bison taxa, but also to
managing for viable bison populations and conserving the
wild bison genome. Boyd et al. review the current state of
bison genetics and what needs to be done to address the
major threats to genetic diversity and integrity—demographic
bottlenecks, founder effects, genetic drift, and inbreeding—all of
which bison have experienced. Although population bottlenecks
can lead to significant loss of genetic diversity, bison appear
to have largely avoided this problem during their population
bottleneck in the late 1800s. Given the good diversity within
the bison gene pool, and recent evidence that shows several
conservation herds are genetically distinguishable, one of the
most important management questions is how to manage the
population genetics of these often relatively small herds. Should
this be accomplished as one large metapopulation or as closed
herds to maintain localised diversity? The best conservation
strategy is to do both, and, where possible, to increase the
size of small herds to attain a large effective population size.
Hybridisation also poses challenges for bison conservation.
Although the introduction of plains bison into wood bison range
has resulted in some hybridisation, the two forms remain distinct
and avoiding further hybridisation is a priority. Much more
widespread, and of greater concern, is the introgression of cattle
genes into the bison genome, a legacy of attempts to cross-
breed cattle and bison that began when bison numbers were
still low in the early 1900s. Genetic testing reviewed by Boyd et
al. indicates that most conservation herds have some level of
cattle-gene introgression in the nuclear and (or) mitochondrial
DNA. By inference this strongly suggests that a vast majority of
commercial herds have cattle-gene introgression. The effects
xvi American Bison: Status Survey and Conservation Guidelines 2010
of introgression on bison biology are largely unknown. No
introgression has been detected in several conservation herds,
which consequently deserve priority attention for maintaining
in reproductive isolation, and as source stock for establishing
new conservation herds. Finally, Boyd et al. note that the
approximately 400,000 bison in commercial herds in North
America, some 93% of the total continental population, are
undergoing artificial selection for domestic traits, such as ease
of handling, body conformation, carcass composition, and so
on. Domestication, whether intentional or not, poses a special
challenge to conserving the wild bison genome.
In Chapter 5, K. Aune and co-authors provide a comprehensive
review of how diseases, particularly those that are “reportable”
according to federal or state/provincial regulations, have a major
influence on bison restoration and management. They describe
the characteristics and implications of nine diseases for bison
conservation, ranging from anthrax and bluetongue to bovine
brucellosis and bovine spongiform encephalopathy. Federal and
state/provincial regulations for, and management responses to, a
particular disease depend on several factors, including potential
effects on bison, threat to livestock and humans, and whether it
is indigenous or exotic to bison and the ecosystem. The authors
describe the complex and difficult management challenges that
diseases present in three of North America’s most important
conservation herds: the plains bison herds of Yellowstone
National Park (YNP) and Grand Teton National Park/National Elk
Refuge that harbour brucellosis, and the wood bison herds in
and around Wood Buffalo National Park that are infected with
both bovine tuberculosis (BTB) and brucellosis. Diseases such
as brucellosis also severely limit the translocation of bison from
infected, important conservation herds, such as the Yellowstone
herd, to establish new herds in new areas because of concerns
about potential transmission to cattle. While the policies and
legal framework for controlling disease in domestic livestock are
well established, they do not work well when applied to wildlife,
including bison, because they often conflict with conservation
goals and our ability to manage and maintain wild populations.
The recent development of national wildlife health strategies in
both Canada and the U.S. could help address this problem.
Chapter 6, by P. Gogan and co-authors, addresses general
biology, ecology, and demographics of bison. Bison are
remarkably adaptable to a wide range of ecosystems and
climatic regimes. Physiologically, bison are much better adapted
to climate extremes than cattle. Behaviourally, bison exhibit a
relatively simple social structure with cow-calf pairs at the core
and, more loosely and somewhat seasonally, large groups of
cows, calves and immature males, and separate, smaller groups
of mature bulls. Bison exhibit individual and group defence
against large predators such as wolves. Historically, plains bison
made seasonal migrations between summer and winter ranges,
in some cases north-south and in others between the prairies