Retaining wild characteristics of
plains bison, and the natural integration of a bison herd
with its associated biota, requires a large herd under
management that allows as much natural selection as possible.
Management activities that weaken or replace natural selection
must be avoided or minimized to the extent practicable.
These activities, termed “artificial selection”,
foster abundant reproduction, rapid animal growth, and
survival. They are a legacy of livestock management for
maximizing herd production.
At least ten interrelated conditions
or activities diminishing natural selection are prevalent
in managing most plains bison herds in the USA.
Small monotonous range:
1) limits herd size, exacerbating genetic drift; 2) limits
mobility, diminishing natural selection for behavior enhancing
wide-ranging habitat choices; 3) lacks selection for characteristics
that support effective and efficient use of biotic and
topographic resources that are absent on the range.
Forced pasture rotations:
replaces socially-mediated habitat choices by bison, eliminating
selection for genes that enhance this behavior.
Frequent capture and handling:
Selects against animals resisting handling in pens and
squeeze chutes. Resisting animals are apt to be injured.
Injured males, especially with broken horns, may have
reduced chances to compete for breeding. Selects for compliant,
lethargic animals. Effects on selection based on natural
competition are at least uncertain.
Selective culling:
Animals that are difficult to capture and handle; cows
that have failed to calve every year; animals that grow
more slowly are culled from the herd, reducing the pool
of animals available for natural selection. Removal of
males and of animals older than about 8 years may be used
to foster an unnatural herd sex/age structure as noted
below. (In contrast, harvesting of mostly yearlings would
minimize replacement of natural selection as discussed
elsewhere on this website. Use “Why Wildness?”
toolbar).
Maintaining a skewed sex/age
structure: Herd productivity is enhanced by maintaining
a low bull/cow ratio among adult animals; and a young
overall age distribution. Often, few, if any, animals
are retained beyond 8 years of age. Likely, no bison grow
old and die on the range, contributing seasonally important
carrion to the local wild food chain. Just as survivors
in an age cohort of animals have demonstrated, for 8 years,
their ability to compete, their further contribution to
the herd genome is eliminated.
Forced weaning: Early
separation of calves from their mothers stimulates cows
to produce calves every year; but will diminish development
of strong social relationships in matrilineal groups that
transmit knowledge of available habitats across generations.
Physiological effects of early weaning are unknown.
Frequent or emergency feeding:
Artificial feeding avoids periodic strong natural selection
for competiveness, energy efficiency and foraging efficiency.
(For the genome, the selective value of “crunch
time” never occurs.)
Disease management:
Preventive management with vaccinations and perhaps control
of internal and external parasites, is common, and required
for bison in some states. Disease problems are minimized
by maintaining a young herd age-structure. Selection for
co-evolution of the host animals with their diseases is
limited or eliminated. Resulting lack of herd resistance
obligates continued artificial management of diseases.
Lack or control of predators:
Wolves, grizzly bears and mountain lions may prey upon
bison, particularly young calves or old, ill, or injured
animals. Wolves, especially, may focus on ill bison, limiting
disease prevalence in the herd and selecting against the
least disease-resistant animals. South of Canada, the
only substantial public herd of plains bison adapted to
living with a natural abundance of these predators is
in Yellowstone National Park. Almost everywhere else,
elimination or control of these predators is the law or
is public policy.
Maintaining a stable herd
at moderate ecological density: Based on a simple
concept (model) of density-dependence, most big-game herds
are managed for herd stability with abundance well below
the natural carrying capacity of the range – of
the forage resources, in particular. This predicts maximum
annual production, early-life health and survival and
year-by-year sustainable harvests of animals. Necessary
harvest each year generally produces a young population
age structure. This livestock production model, commonly
used in wildlife management, is widely applied in managing
plains bison. Consequently, the extremes of natural selection
at occasional low or high population densities are eliminated.
(These extremes have been termed “r” and “K”
selection.)
Among these ten conditions that weaken
or replace natural selection, the three most consistently
present for plains bison south of Canada are having a
small herd on a monotonous small range, and control of
predators and disease. Most plains bison herds are small
because we have not been willing to commit large public
landscapes to bison conservation. Wild public bison are
unwelcome on most public lands, and predators and ungulate
diseases are constrained or prohibited, primarily due
to insistence from the livestock industry.
Moreover, there is a lack of public
understanding and acceptance of distressful components
of natural selection and of associated natural biotic
relationships in wild ecosystems. This is a focus on fates
of individual animals rather than on evolutionary health
of wild populations or the evolved relationships within
complex wild biological systems. Basic components of biotic
diversity and biotic integration are being neglected due
to unrealistic views of nature.
The combined effects of genetic drift
and these numerous practices of artificial management
weaken and replace natural selection for animals best
adapted for living under wild conditions with little human
intervention. Slowly, almost imperceptibly, bison become
adapted, genetically, for life under domestication. Loss
of wild characteristics obligates bison to live with continued
human support in human controlled environments.
In the USA, most plains bison herds
have been managed for about a century with acceptance
of small-herd genetic drift, and with most or all of the
above ten conditions. Concern over ongoing domestication
is a recent conservation issue. However, the ten domesticating
conditions and practices cited here are still abundant
in private, commercial bison herds, in most Tribal herds
and in most public or private “conservation”
herds as well. Moderating or eliminating a few of the
ten conditions and practices can, at best, only slow the
domesticating process; and should not diminish the sense
of urgency to save the wild characteristics of plains
bison.
Plains bison have been largely neglected
in public policies intended to preserve examples of wild
American nature. Prudence requires that a set of plains
bison herds be established with a primary goal of maintaining
wildness. The current set of herds managed under this
mandate is not adequate. Only 13 Department of Interior
plains bison herds, on native range, are managed under
reliable mandates to conserve the genetic diversity and
natural biotic interrelationships of the animals. Yet,
only two of these herds have ranges large enough to allow
managers to avoid most of the above conditions and practices.