Bison
Hunting and "Wildness"
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If the wildness of a bison
herd depends upon being influenced by a preponderance of
natural selection, as defined elsewhere on this website,
is human hunting compatible with wildness? The answer turns,
in part, on the “naturalness” of human predation
for bison. Do we consider hunting as natural selection,
or as artificial selection that only replaces or weakens
natural selection?
Exploring the evolution of bison, we
find that human predation has been a primary selective force
creating modern bison, including many of their wild characteristics.
The prolonged and complex evolution
of modern bison from ice-age species (Bison priscus, Bison
latifrons, Bison antiquus) is discussed in Bailey (2013).
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Throughout glacial and interglacial periods,
natural selective forces affecting these bison included intra-
and inter-species competition, predation, disease, and climate,
including its associated effects on vegetation and forages.But
selection changed near the end of the ice age when bison began
to evolve into the modern species, Bison bison, with integrated
adaptations of anatomy, physiology and behavior.
The large size of early bison suited ice-age
environments, but was especially a response to predation. These
bison lived with at least 13 species of large and/or formidable
predators. There were gray wolves, dhole and dire wolves, short-faced
bears, grizzly and black bears, sabertooth and scimitar cats,
American lions, jaguar, cheetah, puma and men, though humans were
late to become abundant.
Most dangerous among these non-human predators
was the short-faced bear, which dwarfed grizzly bears. Short-faced
bears stood 6-feet tall at the shoulders. Their long legs were
designed for running down large prey.
The large size and large, aggressive horns
of ice-age bison must have been largely an adaptation for predator
defense. Presumably, bison assumed a social “stand and defend”
posture, with smaller, younger bison shielded behind the larger
animals. We still see glimpses of this behavior in modern bison.
However, at the end of the ice age, 8 of the
13 dangerous predators went extinct. This diminished the value
of a stand-and-defend predator strategy. At the same time, a new
predator showed up – humans. These new predators used and
threw spears. A stand-and-defend strategy was useless against
them. These events created a major shift in bison evolution, a
behavioral change from predator-defense to predator-escape. The
evolution of Bison bison began.
Modern bison are smaller than ancestors of
their past – and probably faster with more stamina. The
dominant character of bison shifted from “big and bad”
to great mobility. This evolved change in behavior required congruent
changes in anatomy and physiology. Moreover, the new characteristic
of great mobility offered new possibilities for habitat use in
response to seasonal and weather-related variation in the environment.
All the evolved characteristics of modern bison, for dealing with
both the threats and opportunities of their environment, are congruent
with the characteristic of great mobility.
It seems the mobility strategy was quite effective
against pedestrian human predators, allowing 30-or-more million
bison to persist in North America. In contrast, the ability of
bison to withstand horse-mounted hunters was not tested for long.
Clearly, clever horse-mounted Native Americans were sometimes
able to kill very large numbers of bison in early historic times
(Bailey 2016).
Early accounts indicate that mobility was
an important bison response to human hunters. Both Native-American
and Euro-American hunters used caution not to disturb bison herds
until a full contingent of hunters could be brought up for a “surround”.
Otherwise, the bison were expected to escape over a long distance.
Clearly, human hunting has been a dominant
factor in the evolution of modern bison. Thus, there is no basis
for considering hunting as “unnatural” for the species.
Yet the culling effects of modern hunting may weaken or replace
all other forms of natural selection. This threat is exacerbated
in today’s bison herds for which intensive management (artificial
selection) and small-population effects also weaken and replace
natural selection. Excessive levels of hunting, or of any human-applied
culling, can impel bison herds away from wildness toward domestication,
especially in small herds. (See also the biological definition
of wildness on this website.)
Given the above, how do we judiciously apply
hunting to bison herds for which maintaining wildness is a goal?
Because bison herds vary greatly in size, environments and management
objectives, only general principals are offered here.
It is desirable to retain hunting as a form
of natural selection on any bison herd for which maintaining wildness
is a goal. But attempts to use harvest as a tool for maximizing
bison production, by controlling herd size and sex-age composition,
is an application of livestock management – jeopardizing
wild characteristics and leading to domestication.
For purposes of wildness, it is desirable
that some bison succumb to types of natural selection other than
hunting. This will be easiest to achieve if the herd is large,
permitting considerable human harvest as well as other forms of
mortality. By contrast, with a small bison herd, negative genetic
effects of small population size (inbreeding and genetic drift)
would augment the artificial components of human harvest in weakening
and replacing all other forms of natural selection.