Biological Definitions

To a biologist, the opposite of “wild” is “domestic”. The vast majority of bison are being domesticated as legally defined livestock in private commercial herds. In contrast, only about 2000 plains bison exist in conservation herds south of Canada.

Across America, the major threat to persistence of wild bison is domestication.

But the process of domestication occurs in our conservation herds as well. Valuable wild characteristics of bison are being eliminated (Bailey 2013). Wild plains bison may not endure as our heritage to future generations.

If wild bison are to prevail as a public trust resource, a simple definition – with a clear explanation – is necessary.

Definition: A wild bison herd is subjected to a preponderance of natural selection.

For many readers, this simple definition will be unsatisfactory. It simply substitutes “natural” for “wild”, adding little clarification. Hence, the complexities of natural selection must be addressed to provide real meaning. Warning: for many readers this will require serious concentration on a complex subject. It’s complicated, but it’s very, very important for the future of wild bison.

Natural Selection Revises Bison Genomes with Each New Generation

Natural selection has been a major driver in the evolution that produced all our wildlife, including all their unique and valuable characteristics. Over many generations, whole new species have developed.

But evolution proceeds slowly. At the process level, evolution occurs with each new generation of animals. Evolution includes every change, however small, in the genetic constitution of a population between generations. These changes may go unnoticed, but in time they accumulate and threaten the wild values of bison.

We cannot leave bison to future generations of us. Bison die, but their genes, in their many changing combinations, persist. These combinations determine the qualities of succeeding populations of bison. Thus, if we are to consider our legacy to future generations, we must become aware of the complexities of population genetics. It is an ethical mandate of conservation biology.

Our heritage to the future will be the wildness of bison genomes. A genome is all the different forms of genes (alleles) and their very many combinations, existing across all the animals within a herd.

Bison Genomes Are Incredibly Diverse and Complex

A gene is the heritable unit of DNA at a location on a chromosome. A human chromosome, for example, has thousands of genes, and there are 23 chromosomes. But many genes exist in different forms (alleles), spread across the animals in a population. A population, therefore, may have many, many thousands of alleles, with most alleles having somewhat different effects upon the host animals. Moreover, most animal characteristics depend upon effects of combinations of genes working together. Thus, a population has many, many, many thousands of different allele combinations, dispersed across its animals. Some combinations are more beneficial for survival and reproduction of their host animals; other combinations are less beneficial and some are downright deleterious. Each animal has some mix of these. And with reproduction and each succeeding generation of bison, the alleles and their combinations are reorganized into a new genome.

Natural Selection Is an Inefficient Process

Natural selection cannot operate at the level of alleles. It must favor those animals with the “best” available overall mixtures of gene combinations for reproduction and survival in a current environment. Thus, “poor” alleles survive across generations mostly because some happen to exist with combinations of “good” alleles in some of the animals.

As a result, natural selection is an inefficient and slow process. It is also a conservative process that retains alleles less suited to a current environment. Such alleles may become useful and favored in a new or changed environment. Most important for this discussion, is that – as an inefficient process – natural selection is easily weakened and replaced, especially in small bison populations.

Natural selection is easily weakened and replaced, especially in small bison populations. Inbreeding, artificial selection and genetic drift replace and weaken natural selection.

Opponents of Natural Selection

Three processes weaken or replace natural selection in bison herds. They are inbreeding, artificial selection and a random process called genetic drift.

Inbreeding results from reproduction by closely related animals. Inbred offspring have more pairs of recessive deleterious alleles than do outbred offspring. (Such alleles are not expressed in the host animal when they are paired with different “dominant” alleles.)

Thus, inbred animals have a genetic burden that limits their survival and reproduction. This removes animals from much exposure to natural selection, weakening the ability of natural selection to favor, at the population level, many alleles that would be beneficial in the environment. Essentially, inbreeding diminishes the number of animals available to natural selection.

Inbreeding is a significant issue for small bison herds, especially those with few breeding-age males relative to the number of females.

Inbreeding weakens the ability of natural selection to favor beneficial alleles in the population.

Artificial selection occurs when human decisions or human-created environments determine the survival and reproduction of individual animals. It is most expressed when there is selective culling to control animal characteristics and/or herd size.

However, many human activities – often called wildlife management – contribute to artificial selection. For examples: predator control eliminates selection for animals with the best gene combinations for predator detection, predator defense, seeking habitat security, and predator escape. Population control, perhaps with winter feeding, limits herd size and removes much of the selection for animals best suited in terms of habitat selection, competitiveness, foraging proficiency and energy efficiency, for surviving in occasional severe winters. Vaccinations eliminate selection for animals with the best disease-resistance.

Artificial selection replaces much of natural selection in most bison herds. Artificially selected bison herds will become ever-more dependent upon human support and management to survive and reproduce efficiently, especially in a wild environment. Bison will become a domesticated species.

Genetic drift occurs when random processes determine which animals survive and reproduce, and which alleles are passed to offspring. Some drift is obligatory, as it occurs when chromosomes are split to form every sperm or ovum. In bison, half the chromosomes and their alleles are, essentially, discarded at random as only one ovum and one sperm become successful in forming one calf per year. Drift weakens natural selection. After selection has favored survival of an animal with its unique allele combinations, half the alleles are discarded in producing a calf!

Genetic drift negatively affects a herd genome by diminishing allelic diversity, by allowing deleterious alleles to persist, and by dismantling the adapted wild genome.

As an inefficient process, natural selection works best with large populations. In contrast, drift affects half the herd genome, no matter the herd size. Thus, its influence upon herd evolution is more preponderant over natural selection in smaller herds.

Drift has three negative effects upon a population:

Loss of alleles. Randomness dictates that the proportion of animals carrying a given allele will increase or decrease, due to chance, with each year’s calf crop. Over time, the frequency of an allele may increase, or it may decrease, consistently across some consecutive years. (As every poker player has good and bad streaks of luck!) With time, some alleles will experience too many consecutive “bad” years and decrease to zero. They go extinct in the herd. One study estimates that a herd of 2000-3000 bison will lose 5 percent of its alleles each 100 years. Herd genetic diversity declines and the ability of the herd to adapt, genetically, to future changes in the environment is diminished.

It cannot be good if the composition and organization of a herd’s genome is drifting at random. Yet, negative effects of genetic drift are commonly ignored in wildlife management.

Persistence of deleterious alleles. To the extent that natural selection is weakened by drift, alleles that negatively affect survival and reproduction are less promptly diminished or removed from a population through natural selection. Deleterious alleles can persist when combined with a preponderance of valuable alleles.

Dismantling the wild genome. In a large wild bison population, with effective natural selection, we expect that a large proportion of the animals will have a large proportion of allele combinations that favor survival and reproduction in the wild environment. This organization of the herd genome is maintained with continued natural selection. When natural selection is weakened by random drift (and/or replaced by artificial selection), the wild herd genome is dismantled and disorganized. It becomes less effective, less efficient, for operating in the wild environment.

Wild Bison and Their Habitat Requirements

With the above as context, wild bison are those living with a preponderance of natural selection. For effective natural selection, bison must live in a large herd and roam over a large, diverse landscape that presents the diversity of opportunities and challenges that constitute the full array of natural selection.

A large, diverse habitat is required to provide the full array of natural selection for bison.

In contrast, most plains bison today are in small herds living in small habitats. They are subjected to much artificial selection, augmented by a preponderant genetic drift, dismantling the wild genomes. Gradual domestication is inevitable.
For retention of wildness, this Coalition promotes at least 1000 bison on at least 100 square miles of diverse, quality bison habitat. This would allow expression and maintenance of wild characteristics of bison, including their most basic characteristic of great mobility.

The Perplexity of Wildness

Wildness is much more than a mere romantic notion. It is a legacy of living and dying that occurred in a species’ extensive past. It is the complex, genetically organized, accumulation of diversity and adaptedness that fits a species to its environment. It has provided animals that are efficient, self-sustaining, and a valuable human resource.

Wildness is resilient, yet can be eliminated – rapidly in small populations; slowly and imperceptibly in larger herds. It is happening with many species and will continue until the profession of wildlife management recognizes and addresses the issue. The definition and understanding of wildness is necessary to realize how the present array of bison herds in Montana is not adequate for retaining wild bison.

Aside from all this, we know wildness when we recognize the awe, allure and adventure of the wild. We must not deny these feelings, lest we diminish wild bison and ourselves. And the science of wildness, alluded to here, only adds to that awe, allure and adventure.

Jim Bailey, 2018

Bailey, J. A. 2013. American Plains Bison: Rewilding an Icon. Sweetgrass Books, Helena, Montana. 238pp.