American Bison - Buffalo Field Campaign

composition and function, as well as being integrated into
the larger landscape, and supporting sustainable human
livelihoods. Ecological restoration involving bison as an integral
component of ecosystems faces two major challenges: 1)
how to undertake restoration across large areas with diverse
land-use and ownership patterns; and 2) how to undertake
restoration in a way that improves both biodiversity and human
wellbeing. Large-scale ecological restoration involves biological
and social complexity. Attitudes, economics and politics, from
local to regional and international scales, will shape the future
of bison conservation on occupied lands. These challenges are
addressed in Chapter 10.
1.5 Conserving the Wild Character and
Genome of Bison
Bison in captive herds may be managed to achieve various
objectives, including the ecological services that bison provide
(e.g., grazing, nutrient cycling, and terrain disturbance),
education and display, commercial production, and
conservation of bison as wildlife. Conserving bison as wildlife
is not necessarily served by managing a population for other
purposes. For example, the ecological effects of herbivory may
be achieved by grazing a variety of livestock species. Although
some rangelands formerly used for cattle production have
been converted to bison production, the substitution of bison
for cattle production does not, by itself, necessarily contribute
to bison conservation, or to ecological restoration of bison
as wildlife. Similarly, display herds may serve conservation
education objectives without otherwise contributing to species
conservation.
In the absence of intentional policies and actions to conserve
the wild character and genome of bison, captivity and
commercialisation can lead inadvertently or intentionally to
a variety of effects that may be deleterious to bison as a
wildlife species in the intermediate to long term (Chapter 4).
These include effects on the genome: founder effect; reduced
genetic diversity; persistence and phenotypic penetration
of deleterious genes; or inadvertent selection for heritable
morphology, tameness or adaptation to captivity. Small
populations are particularly susceptible to such effects. The sex
and age structure of captive conservation populations may be
manipulated to reduce the risk of escape, remove aggressive
animals, or to alter fecundity or the rate of population increase.
The age composition of males in captive herds is typically
substantially different from wild populations.
The common practice in captive commercial herds of eliminating
males, before they become morphologically and behaviourally
mature, poses a challenging question about the roles of
mate competition and natural selection for fitness in such
populations. In general, selection pressures on captive wildlife
are substantially different from those in the wild. O’Regan
and Kitchener (2005) posited that domestication may occur
inadvertently in captive wild mammals through passive selection
for individuals behaviourally suited to captivity, with concomitant
morphological changes over several generations. Most changes
are thought to result from increasing paedomorphosis, whereby
juvenile characteristics are retained in the adult form of an
organism (O’Regan and Kitchner 2005). Clutton-Brock (1999)
described changes in large mammals under captive conditions
including reduced body and brain size, altered external
appearance, the gaining of a fat layer beneath the skin and a
reduction of the facial region. Inadvertent selection for tameness
and adaptation to a captive environment is typical in mammals
(Frankham et al. 1986), and in addition to altering “wildness”,
can reduce the chances for successful reintroduction of captives
into the wild. A loss of response to predators and alteration
of defensive and sexual behaviours have also been reported
in captive wildlife (Price 1999; 2002). Many commercial bison
producers directly select for marketable traits such as early
maturity, coat colour, body size and conformation. The latter
“show ring traits” are promoted in bison industry advertisements,
publications and at auctions.
The large size of the commercial captive population is the basis
for a popular misconception that the species is “secure”, leading
wildlife management agencies to ignore actions necessary for
conservation of wild type bison. Today, among North American
jurisdictions, there is a confusing array of classifications of bison
as wildlife, domestic livestock, or both (Chapter 8).
Hybridisation with cattle is another serious challenge for bison
conservation. In the U.S., Canada, and Europe, agricultural
interests attempted to develop an improved range animal by
hybridising bison and cattle. Forced-mating of bison and cattle
can be readily achieved in a controlled environment. However,
they preferentially mate with their own species under open
range conditions (Boyd 1908; Goodnight 1914; Jones 1907).
In Europe, the European bison (Bison bonasus), a relative of
the American bison, and the aurochs (Bos taurus primigeneus),
progenitor of modern cattle, were sympatric, yet evolutionarily
divergent, units. Typical of sympatric species occupying similar
trophic niches, behavioural and ecological specialisation
provides niche separation, leading to reproductive isolation
and progressively to speciation (Bush 1975; Rice and Hostert
1993). Species divergence and reproductive incompatibility
are evident from the low fertility of first generation (F1) bison x
cattle offspring (Boyd 1908; Steklenev and Yasinetskaya 1982)
and the difficulty producing viable male offspring (Boyd 1914;
Goodnight 1914; Steklenev and Yasinetskaya 1982; Steklenev et
al. 1986). Unfortunately, forced hybridisations between B. bison
and Bos taurus in North America have left a legacy of cattle
mitochondrial (Polziehn et al. 1995; Ward et al. 1999) and nuclear
DNA (Halbert 2003; Halbert et al. 2005). This introgression is
American Bison: Status Survey and Conservation Guidelines 2010 3