American Bison - Buffalo Field Campaign
American Bison - Buffalo Field Campaign
American Bison - Buffalo Field Campaign
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Table 9.1 Ecosystem processes that bison can strongly influence. See<br />
Hobbs (1996); Knapp et al. (1999); Larter and Allaire (2007); and Truett<br />
et al. (2001).<br />
Process Description<br />
Create patches Grazing can produce a dynamic<br />
mosaic of vegetation patches that<br />
differ in seral stage and that differ due<br />
to variations in grazing intensity<br />
Enhance nutrient<br />
cycling rates<br />
Enhance habitat<br />
quality<br />
3) Preserve genetic integrity and health. Maintain bison<br />
lineages and carefully evaluate all movements of bison<br />
between populations. Consider potential genetic<br />
consequences of all management actions, especially for<br />
small herds.<br />
<strong>Bison</strong> grazing can enhance nutrient<br />
turnover and change dominant system<br />
mode from detritus-decomposition to<br />
consumption-defecation<br />
<strong>Bison</strong> grazing can increase habitat<br />
suitability for prairie dogs, pronghorn,<br />
and other species<br />
Modify fire regimes <strong>Bison</strong> consume fine fuels and create<br />
trails and trampled areas that reduce<br />
fire intensity and extent, and modify<br />
the effect of fire on vegetation<br />
heterogeneity<br />
Create disturbances Trampling and wallows create<br />
seedbeds for some species; localised<br />
tree stands that are not tightly clumped<br />
are susceptible to major damage by<br />
rubbing, horning, and thrashing of<br />
bison.<br />
Stimulate primary<br />
production<br />
<strong>Bison</strong> grazing removes senescent<br />
material from the sward and increases<br />
light penetration, nutrient availability,<br />
and growth<br />
Disperse plant seeds <strong>Bison</strong> transport seeds in leg fur and<br />
gut, and may enhance establishment<br />
(of native and exotic plants) via<br />
consumption, seed coat digestion, and<br />
defection in nutrient-rich media.<br />
Maintain floral<br />
diversity<br />
Support carnivores<br />
and scavengers<br />
<strong>Bison</strong> grazing can result in greater<br />
grass and forb species diversity<br />
<strong>Bison</strong> are prey to some large<br />
carnivores, and bison carcasses can<br />
contribute to supporting scavengers.<br />
4) Routine assessment is central to science-based<br />
conservation of bison. Routine monitoring and evaluation<br />
of demographic processes, herd composition, habitat, and<br />
associated ecological processes are central to evaluating<br />
herd health and management efficacy. Assessments are<br />
necessary to anticipate or respond to conservation needs<br />
and sound data is the basis for informed management.<br />
The scientific basis and rational of principles for conserving<br />
bison is provided in the more detailed guidelines in this chapter<br />
86 <strong>American</strong> <strong>Bison</strong>: Status Survey and Conservation Guidelines 2010<br />
and other chapters that review bison ecology, genetics, and<br />
ecological restoration.<br />
9.2 Guidelines for Population and<br />
Genetic Management<br />
The general goals for population and genetic management are to<br />
achieve and sustain a population with a healthy level of genetic<br />
variation and a sex and age composition typical of viable wild<br />
bison populations. Management actions needed to achieve<br />
these goals will vary with the size, history, and circumstances<br />
of each particular population. In this section, we articulate<br />
more specific management objectives, summarise background<br />
information relevant to our recommendations (see also Chapter<br />
6), and provide both general and specific guidelines.<br />
In bison, loss of genetic variation is a concern primarily when the<br />
number of actively breeding animals or the founding population<br />
size is small. Our best estimates are that bison populations<br />
can generally be considered “not small” (for genetic purposes)<br />
when they exceed about 1,000 animals, the population has<br />
approximately equal numbers of bulls and cows, and the size<br />
of the population is stable. For the purposes of this report,<br />
the genetic objective is to attain a 90% probability of retaining<br />
90% of selectively neutral genetic variation for 200 years. This<br />
objective is less stringent than some published objectives,<br />
and thus our estimates for sustainable population sizes are<br />
smaller than those that result from estimates based on more<br />
conservative criteria (Reed et al. 2003; Soule et al. 1986). In all<br />
populations, the rate of loss of genetic diversity is directly related<br />
to how rapidly individuals in a population replace themselves<br />
(generation time) and to the size of the breeding population.<br />
Most guidelines for genetic management in this document can<br />
be understood in the context of just these two factors.<br />
Most populations are not uniform, but have genetic variation<br />
related to the spatial substructure of the population (Manel et<br />
al. 2003). Demographic and genetic substructure occurs at<br />
a large geographical scale due to traditional use of particular<br />
parts of a range (e.g., breeding range fidelity, seasonal ranges,<br />
calving areas) by segments of a population (e.g., bison in YNP;<br />
Christianson et al. 2005; Gardipee 2007; Gogan et al. 2005;<br />
Halbert 2003; Olexa and Gogan 2007). Within herds, bison are<br />
thought to form family groups (i.e., matrilineal groups, mother<br />
cows with their preparturient daughters) and these family<br />
groups constitute fine-scale population structuring. These types<br />
of population structure are important because they increase<br />
the likelihood that animal removals without plans to explicitly<br />
accommodate substructures of cows could disproportionately<br />
impact a particular segment of the population and result in<br />
a greater loss of genetic diversity than necessary. Removal<br />
strategies should be designed to accommodate the potential<br />
spatial structure of herds, and institute procedures that ensure