American Bison - Buffalo Field Campaign

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Table 9.1 Ecosystem processes that bison can strongly influence. See Hobbs (1996); Knapp et al. (1999); Larter and Allaire (2007); and Truett et al. (2001). Process Description Create patches Grazing can produce a dynamic mosaic of vegetation patches that differ in seral stage and that differ due to variations in grazing intensity Enhance nutrient cycling rates Enhance habitat quality 3) Preserve genetic integrity and health. Maintain bison lineages and carefully evaluate all movements of bison between populations. Consider potential genetic consequences of all management actions, especially for small herds. Bison grazing can enhance nutrient turnover and change dominant system mode from detritus-decomposition to consumption-defecation Bison grazing can increase habitat suitability for prairie dogs, pronghorn, and other species Modify fire regimes Bison consume fine fuels and create trails and trampled areas that reduce fire intensity and extent, and modify the effect of fire on vegetation heterogeneity Create disturbances Trampling and wallows create seedbeds for some species; localised tree stands that are not tightly clumped are susceptible to major damage by rubbing, horning, and thrashing of bison. Stimulate primary production Bison grazing removes senescent material from the sward and increases light penetration, nutrient availability, and growth Disperse plant seeds Bison transport seeds in leg fur and gut, and may enhance establishment (of native and exotic plants) via consumption, seed coat digestion, and defection in nutrient-rich media. Maintain floral diversity Support carnivores and scavengers Bison grazing can result in greater grass and forb species diversity Bison are prey to some large carnivores, and bison carcasses can contribute to supporting scavengers. 4) Routine assessment is central to science-based conservation of bison. Routine monitoring and evaluation of demographic processes, herd composition, habitat, and associated ecological processes are central to evaluating herd health and management efficacy. Assessments are necessary to anticipate or respond to conservation needs and sound data is the basis for informed management. The scientific basis and rational of principles for conserving bison is provided in the more detailed guidelines in this chapter 86 American Bison: Status Survey and Conservation Guidelines 2010 and other chapters that review bison ecology, genetics, and ecological restoration. 9.2 Guidelines for Population and Genetic Management The general goals for population and genetic management are to achieve and sustain a population with a healthy level of genetic variation and a sex and age composition typical of viable wild bison populations. Management actions needed to achieve these goals will vary with the size, history, and circumstances of each particular population. In this section, we articulate more specific management objectives, summarise background information relevant to our recommendations (see also Chapter 6), and provide both general and specific guidelines. In bison, loss of genetic variation is a concern primarily when the number of actively breeding animals or the founding population size is small. Our best estimates are that bison populations can generally be considered “not small” (for genetic purposes) when they exceed about 1,000 animals, the population has approximately equal numbers of bulls and cows, and the size of the population is stable. For the purposes of this report, the genetic objective is to attain a 90% probability of retaining 90% of selectively neutral genetic variation for 200 years. This objective is less stringent than some published objectives, and thus our estimates for sustainable population sizes are smaller than those that result from estimates based on more conservative criteria (Reed et al. 2003; Soule et al. 1986). In all populations, the rate of loss of genetic diversity is directly related to how rapidly individuals in a population replace themselves (generation time) and to the size of the breeding population. Most guidelines for genetic management in this document can be understood in the context of just these two factors. Most populations are not uniform, but have genetic variation related to the spatial substructure of the population (Manel et al. 2003). Demographic and genetic substructure occurs at a large geographical scale due to traditional use of particular parts of a range (e.g., breeding range fidelity, seasonal ranges, calving areas) by segments of a population (e.g., bison in YNP; Christianson et al. 2005; Gardipee 2007; Gogan et al. 2005; Halbert 2003; Olexa and Gogan 2007). Within herds, bison are thought to form family groups (i.e., matrilineal groups, mother cows with their preparturient daughters) and these family groups constitute fine-scale population structuring. These types of population structure are important because they increase the likelihood that animal removals without plans to explicitly accommodate substructures of cows could disproportionately impact a particular segment of the population and result in a greater loss of genetic diversity than necessary. Removal strategies should be designed to accommodate the potential spatial structure of herds, and institute procedures that ensure
animals are proportionately removed from different population segments. This could potentially be accomplished by removing animals from different parts of the range. A variety of factors can lead to increased rates of genetic diversity loss. After accounting for population size, the most important factors are likely to be non-random mating (i.e., a few bulls are responsible for siring most calves), skewed sex ratios, and large variation in population size. 9.2.1 Guidelines that apply to most conservation herds Very few conservation herds will persist without the need for some form of population control. Many guidelines in this chapter were included with the specific intent to support development of informed population management plans. Many of the following guidelines apply to most conservation herds, and are likely to be included in comprehensive management plans for conservation herds: 1) Maintain a sex ratio with neither sex constituting more than 60% of the population. Ideally, the adult sex ratio will be slightly female biased (e.g., 55 cows per 100 animals), reflecting observations that mortality rates of males tend to be slightly greater than those for females. Avoiding a high ratio of females to males helps ensure participation in mating and transfer of genetic diversity by a larger number of bulls. In large populations, mating competition will likely be sufficient when there are 20 or more mature bulls (six years old and older) per 100 cows. Maintaining mating behaviour, as noted above, calls for a more equal sex ratio. 2) Avoid removing a significant proportion of the population. For populations subjected to population control actions, culling should be on a yearly, or every other year, schedule, rather than periodically at longer intervals. We cannot offer a definitive definition of ‘significant’, as the effects of population fluctuations will be greater as population size diminishes and varies with other circumstances. As a general guideline, we suggest limiting removals of animals to less than 30% of the population; 3) Avoid disproportionate removal of matrilineal female groups (mother cows and their preparturient daughters). More specifically, attempt to retain the older cows matrilineal groups; 4) Remove animals from all spatial segments of the population; 5) Emulate natural mortality patterns—higher mortality/ removal rates for juveniles and old age classes (more than 15 years); 6) In small populations, consider actions that reduce variation in the breeding success among individuals. This could be accomplished by reducing the opportunities for continued breeding by highly successful bulls. 7) Avoid human selection for market traits such as docility, carcass composition, body shape, or productivity, as such interventions contradict natural selection and conservation of genetic variability; 8) Routine supplemental feeding to increase productivity, or to support a population size that exceeds range carrying capacity, is discouraged for conservation herds; 9) Where practical, the full suite of natural limiting factors should be allowed to influence populations, including winter deprivation and predation. This will result in variable rates of reproduction and survival. The need for active genetic management will vary with herd size, genetic composition, and management goals. In general, genetically diverse herds with more than 1,000 animals are unlikely to require active management to retain most of their genetic diversity for the next 200 years (Gross et al. 2006). Hedrick (2009) suggests a herd size of 2,000-3,000 to avoid inbreeding depression. In very small herds (fewer than about 250 animals), long-term genetic health will require occasional supplementation with genetic material from other herds. The exact number of animals needed to supplement a particular herd will vary with the genetic composition of the source and target herds, but a supplement of four to five breeding animals per decade should be sufficient for long-term herd genetic health (Wang 2004). In addition to the guidelines below, managers should follow the IUCN guidelines for translocation of wild animals between established herds, being especially careful about genetic purity (i.e., cattle genes and geographically appropriate sources of stock) and diseases (http://www.kew. org/conservation/RSGguidelines.html). Active management to retain genetic variation (other than translocations) may be most important for intermediate-sized populations with about 250-750 animals because this is the size range where active management may prevent or greatly reduce the need for translocating animals to ensure long-term the genetic health of a herd (Gross et al. 2006). For conservation herds, the overall objective is to retain allelic diversity, which is the best indicator of the genetic resources available to the population. By contrast, genetic heterozygosity may be a better short-term indicator of the mating structure of the herd. In addition to the guidelines provided above, removal of young animals, prior to their first breeding, can significantly enhance the retention of genetic diversity (Gross et al. 2006). Removal of young animals to preserve genetic diversity may seem counterintuitive. Genetic material is lost only when animals in a population are replaced. Removal of young animals increases the length of the generation (replacement) interval, and this thereby prolongs the retention of genetic material. American Bison: Status Survey and Conservation Guidelines 2010 87
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American Bison Status Survey and Co
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American Bison Status Survey and Co
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Table of Contents Acknowledgements
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6.3 Demographics ..................
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9.6 Active Management: Handling, He
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This manuscript is the product of m
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ABS American Bison Society ABSG Ame
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The publication of this IUCN Americ
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and foothills. Bison have a profoun
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Chapter 1 Introduction: The Context
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composition and function, as well a
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Chapter 2 History of Bison in North
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Figure 2.1 Original ranges of plain
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Charles Alloway (Manitoba), Charles
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nomadic “Plains Indian Culture”
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Chapter 3 Taxonomy and Nomenclature
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demonstrate that Bison and Bos were
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from their original habitat near th
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Chapter 4 Genetics As a science, po
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Selection for diversity in one syst
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cross, however, the latter is more
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the conservation of the wild specie
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Chapter 5 Reportable or Notifiable
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one) followed by its widespread dis
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cattle at similar levels to S19 (Ch
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long as 156 days post-infection. So
Page 53 and 54: and elk herds migrate across severa
Page 55 and 56: These concepts are being developed
Page 57 and 58: Chapter 6 General Biology, Ecology
Page 59 and 60: leave the herd prior to calving or
Page 61 and 62: historically dependent on a combina
Page 63 and 64: 6.2.1.2.1 Northern mixed grasslands
Page 65 and 66: woodland caribou (Rangifer tarandus
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Page 69 and 70: Table 6.4 Age-specific reproductive
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Page 73 and 74: Chapter 7 Numerical and Geographic
Page 75 and 76: Sixty-two plains bison and 11 wood
Page 77 and 78: Figure 7.4 Representation of plains
Page 79 and 80: Plate 7.3 Male plains bison sparrin
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Page 85 and 86: Table 8.1 Current legal status of p
Page 87 and 88: Table 8.1 (continued) Country/ Stat
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Page 111 and 112: Table 9.4 Important considerations
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Page 123 and 124: • Creating education, awareness a
Page 125 and 126: 10.3 The “Ecosystem Approach” f
Page 127 and 128: anywhere without engaging stakehold
Page 129 and 130: Interventions (e.g., supplemental f
Page 131 and 132: Agabriel, J. and Petit, M. 1996. Qu
Page 133 and 134: Byerly, R.M., Cooper, J.R., Meltzer
Page 135 and 136: Dragon D.C. and Rennie, R.P. 1995.
Page 137 and 138: Gilpin, M.E. and Soulé, M.E. 1986.
Page 139 and 140: Joern, A. 2005. Disturbance by fire
Page 141 and 142: Matthews, S.B. 1991. An assessment
Page 143 and 144: Possingham, H.P., Davies, I., Noble
Page 145 and 146: Shaw, J.H. 1995. How many bison ori
Page 147 and 148: van Zyll de Jong, C.G. 1986. A Syst
Page 149 and 150: Appendix A North American conservat
Page 151 and 152: Plains bison (continued) State/Prov
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INTERNATIONAL UNION FOR CONSERVATIO
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