Ten Common
Bison Management Practices
Weaken and Replace
Natural Selection


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.


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