Current Literature on Ecology and Management of Bison
Abstract: While ecological and conservation consequences of combining animals of varied genetic backgrounds have been widely discussed the demonstration of effects that stem from lineage mixing remains elusive. Since management agencies relocate populations or supplement them with individuals regularly, the opportunity for either inbreeding or outbreeding depression may be high; still, any putative effects will go unnoticed without detailed knowledge of life-history and behaviour. Here, we report potential consequences of lineage mixing in a restored population of North American Bos bison studied for five years. In 1984 two allopatric lineages became sympatric in Badlands National Park, South Dakota, they differed in both founding population size and the number of demographic bottlenecks experienced since 1907. Measures of reproductive variance in both sexes were employed to estimate effective population size based on 261 copulations and the survivorship of calves between 1985 and 1989. We assumed that the reproductive variance and mortality documented in this study are representative of the bison's recent past and based on this assumption we calculated N-e separately for each generation for which the lineages were allopatric. Four potential correlates of fitness were studied in the new sympatric population: (1) female fecundity; (2) juvenile survival; (3) growth rates, and (4) female age at puberty. Of these, neither female fecundity nov juvenile survival was associated with lineage but growth rates were more rapid and ages at puberty were lower for F-1 purebred (inbred) juveniles than for F-1 hybrid (outbred) juveniles. Possible consequences of this variation in the F-1 generation include (1) higher winter mortality in the slower growing line as well as (2) decreased lifetime production of young; both are life-history parameters that could be interpreted as long-term selection against outbreeding. However, these data by themselves do not constitute support for an outbreeding depression hypothesis. The failure of males from one lineage to mate at all prevented the possible combinations of the F-1 generation needed for the appropriate statistical contrasts. Nevertheless, these interpretations (1) substantiate a level of variation in life-history parameters stemming from lineage mixing; and (2) suggest that advice regarding prudent conservation strategies must be sought concerning the generic histories of individuals and populations to be selected for re- introduction. This applies to both wild and captive populations. The prevalence of outbreeding and inbreeding tolerances within populations of managed and protected species needs verifiable documentation.
Abstract: The aspen Populus tremuloides parkland that forms the northern margin of the North American grassland or prairie has been variously attributed either individually or in different combinations to the ecological effects of prairie fire, fire suppression, frequent drought, and grazing. Plains bison Bison bison bison, formerly abundant on the western North American plains, inhibited growth of aspen by browsing, wallowing, trampling and toppling. Historical references show that aspen populations have expanded over the past century, and fossil pollen evidence suggests that the expansion occurred mainly after the near extinction of bison but before European homesteading and subsequent fire suppression in the late 1800s. We suggest that a prehistoric cycle of grassland, fire, aspen suckering, bison activity, and return to grassland was interrupted by the removal of bison, allowing aspen expansion.
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Abstract: A urinary collection device is described for use in metabolism studies on female bison (Bison bison) and cattle. Separating urine from feces, and collecting all urine produced by female animals in metabolism stalls present difficulties. Catheters are usually used on animals in confinement, but often with varying degrees of success. Thus, an external device designed to divert urine into collection receptacles was developed. The urine collection apparatus was used successfully in six 8- day metabolism trials conducted during 1991 and 1992.
Abstract: Two abundant tallgrass prairie forb species, Ambrosia psilostachya and Vernonia baldwinii, are commonly found intact in patches where the grasses have been selectively grazed by bison. Microclimatic patterns and physiological responses of these forbs were measured in grazed and ungrazed patches. These experiments demonstrated that bison herbivory indirectly enhanced water availability and productivity of forbs growing in grazed patches. This was due primarily to the reduction in transpiring grass leaf area in grazed patches and an increase in light availability. In grazed patches, incident light at forb mid-canopy height was 53% greater than ungrazed sites at midseason and soil temperatures were always warmer (e.g., 10- degrees-C at 5 cm), perhaps enabling forbs to initiate growth earlier in the spring. Enhanced leaf xylem pressure potential and stomatal conductance in plants in grazed areas were most evident when water availability was low (i.e., late in the growing season and over short-term dry periods characteristic of the tallgrass prairie environment). Relative to individuals in ungrazed areas, end-of-season biomass of A. psilostachya was 40% greater and reproductive biomass and head number of V. baldwinii was 45% and 40% greater, respectively, in plants in grazed patches. A favorable growing environment maintained in grazed patches during periods of water limitation enhances carbon gain in forbs leading to increased biomass and potential fitness.
Abstract: Between 1986 and 1991, 155 wood bison (Bison bison athabascae) (33 adult females, 92 adult males, twelve 6 mo-old calves, eighteen 1 to 2 mo-old calves) in the Mackenzie Bison Sanctuary, Northwest Territories, Canada, and adjacent area were captured by dart immobilization. Initial trials with carfentanil, xylazine and R51163 as immobilizing agents were conducted. Subsequently, carfentanil alone, or in combination with xylazine, was used. Small doses of xylazine were used when required to control head and hind limb movement of recumbent bison. The mean dose of carfentanil used was 7.0 mu g/kg. Narcotic antagonists used were naltrexone, naloxone and M5050. Narcotic recycling was seen in animals treated with naloxone and low doses of naltrexone. Furthermore recycling was suspected in the deaths of several animals treated with these antagonist regimes. No recycling was seen when doses of naltrexone in excess of 90:1 naltrexone: carfentanil were used. We recommend using a naltrexone: carfentanil dose in excess of 125:1 to ensure uneventful recovery.
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Abstract: Grazed and ungrazed sites subjected to different fare frequencies were sampled on the Konza Prairie Research Natural Area in northeast Kansas after 4 years of bison grazing (1987-1991). The objective was to study effects of bison grazing on plant species composition and diversity components (plant species richness, equitability, and spatial heterogeneity) in sites of contrasting fire frequency. Cover and frequency of cool-season graminoids (e.g. Poa pratensis L., Agropyron smithii Rydb., Carer spp,) and some forbs (e.g. Aster ericoides [A, Gray] Howell, and Oxalis stricta L.) were consistently higher in sites grazed by bison than in ungrazed exclosures, whereas the dominant warm-season grasses (Andropogon gerardii Vitman, Sorghastrum nutans [L.] Nash, Panicum virgatum L., Schizachyrium scoparium [Michx.] Nash) and other forbs (e.g. Solidago missouriensis Nutt.) decreased in response to bison. Plant species diversity (H') and spatial heterogeneity in all areas sampled were significantly increased by bison. Increased heterogeneity and mean species richness in grazed prairie (40 species per sample site) compared to ungrazed prairie (29 species per site) were likely a result of greater microsite diversity generated by bison, whereas preferential grazing of the dominant grasses and concomitant increases in subordinate species resulted in an increase in equitability of species abundances. Species/area relationships indicated greater effects of bison on plant species richness with increasing sample area. Increases in plant diversity components associated with bison grazing were generally greater in annually burned than in I-year burned sites. Effects of ungulate grazers on floristic diversity have important implications given recent evidence that plant species diversity and the compositional and production stability of grassland plant communities are positively related.
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Abstract: The Greater Yellowstone region's bison-brucellosis controversy has triggered troublesome proposals giving federal and state agriculture agencies jurisdiction over wildlife to eradicate a domestic livestock disease. Many of the region's bison (Bos bison) and elk (Cervus elaphus) carry the bacterium Brucella abortus, which can cause brucellosis. Local livestock officials fear bison and elk could transmit brucellosis to domestic livestock, jeopardizing state brucellosis class-free status. However, no cases of such transmission in an open range setting have been verified scientifically. Various federal and state agencies have jurisdiction over the region's wildlife and livestock; these agencies are having real difficulty reaching consensus on how to address brucellosis in the wildlife populations. Montana and Idaho recently vested state livestock officials with jurisdiction over bison leaving Yellowstone National Park (YNP), and the U.S. Department of Agriculture's Animal, Plant, and Health Inspection Service (APHIS) has indicated it may propose regulations asserting jurisdiction over bison. An interim bison management plan, the result of a recent court settlement, provides for the National Park Service (NPS) to participate in capturing, testing, and slaughtering Yellowstone's bison, but makes no provision for addressing brucellosis in elk. The region's brucellosis problem could be adequately addressed through a risk management disease control policy rather than a costly and perhaps fruitless eradication effort. Such an approach can be implemented without the unwelcome precedent of livestock officials taking jurisdiction over wildlife.
Abstract: During the past 20 years Bison (Bison bison athabascae) numbers have increased and Moose (Alces alces) numbers appear to have decreased within the Mackenzie Bison Sanctuary. In adjacent peripheral areas near Mink Lake Moose densities were twice that in the Mackenzie Bison Sanctuary. Wolf (Canis lupus) activity was greater in the Mackienzie Bison Sanctuary than in the Mink Lake area. Although Bison made up a larger proportion of the Wolf diet (based upon scat analysis) in the Mackenzie Bison Sanctuary than in the Mink Lake areas, Moose made up a significantly greater (P<0.001) proportion of the Wolf diet than expected given the availability of prey biomass in both the Mackenzie Bison Sanctuary and Mink Lake areas. Given that Moose made up a similar proportion of the diet in both areas, and that there was a two-fold difference in Moose densities between area, Wolf predation may be destabilizing and exacerbating the decline in Moose numbers.
Abstract: The perennial bunchgrass little bluestem (Schizachyrium scoparium [Michx.] Nash) was examined in a 5-yr study on tallgrass prairie to determine how fire influences its use by bison and its responses to grazing. On unburned prairie, bison grazed only 5% of the available little bluestem, selecting it only 30% as frequently as big bluestem, the dominant co-occurring species. On burned prairie, grazing frequency of little bluestem was over 3-fold greater and equal to that of its dominant neighbor. Grazing frequency of little bluestem was affected by plant size (basal area). On burned sites, plants of intermediate size classes were least abundant (<10% of total) but were grazed most frequently (>50%). Small plants were most abundant but were grazed least frequently. Density, tiller numbers, and basal area of little bluestem were significantly greater in annually burned compared to infrequently burned sites but were decreased by > 50% in grazed compared to ungrazed sites. Grazing shifted the population size distribution toward higher frequencies of smaller individuals (< 50 cm2 basal area), whereas burning increased the frequency of large (> 200 cm2 basal area) individuals. In unburned prairie, little bluestem accumulates a persistent clump of standing dead tillers that appear to serve as a physical deterrent to grazing. Although burning enhances its growth, it also removes its canopy of dead tillers exposing the plant to grazers. The shift in population structure toward a high frequency of smaller (and perhaps less drought- or grazing-tolerant) individuals may contribute to the decline of little bluestem populations under persistent grazing. Thus, plant growth form, population size structure, and fire interact to influence bison grazing patterns and responses of little bluestem to grazing on tallgrass prairie.
Abstract: Leafy spurge (Euphorbia esula), smooth brome (Bromus inermis), Japanese brome (B, japonicus), and downy brome (B. tectorum) are exotic plant species that dominate and displace native forage species throughout much of central North America. However, information on how exotic plant infestations affect native ungulate use of habitat is limited. We used pellet-group densities to estimate use of habitat by bison (Bos bison), elk (Cervus elaphus), and deer (Odocoileus spp.) during 1992-93 growing seasons within 4 exotic plant- infested and 4 comparable noninfested grassland habitats in Theodore Roosevelt National Park, North Dakota. We used twig count and twig measurement methods to estimate use of browse during summer (1992) and winter (1992-93), respectively, for both leafy spurge-infested and noninfested woodland habitats. Bison use of 2 leafy spurge-infested grassland habitats averaged 83% less than that for noninfested sites (P < 0.001). Deer pellet-group densities,normally highest within creeping juniper (Juniperus horizontalis;)-little bluestem (Schizachyrium scoparium) habitat, were reduced less than or equal to 70% by infestations of leafy spurge (1992, P = 0.035; 1993, P = 0.002). Use of bromegrass-infested grassland by bison, elk, and deer was similar to that for noninfested sites for 1992 and 1993 (P > 0.05). Use of browse in green ash (Fraxinus pennsylvanica)-chokecherry (Prunus virginiana) habitat during summer and winter was reduced an average of 32% by infestations of leafy spurge (P < 0.05). The reduction in native ungulate use of leafy spurge-infested sites may be attributed to lower forage production in infested sites as well as simple avoidance.
Abstract: The relationship between fine-scale spatial patterns of forage abundance and the feeding patterns of large ungulates is not well known. We compared these patterns for areas grazed in winter by elk and bison in a sagebrush-grassland landscape in northern Yellowstone National Park. At a fine scale, the spatial distribution of mapped feeding stations in 30 m x 30 m sites was found to be random where there were no large patches devoid of vegetation. In areas similar to the mapped sites, the underlying spatial distribution pattern of biomass was also determined to be random. At a broad scale, forage biomass differed among communities across the northern range but forage quality did not. These results suggest that ungulates are feeding randomly within forage patches (fine scale) but may select feeding sites based upon forage abundance at broader, landscape scales. Contrary to what has been suggested in other systems, ungulates were not 'overmatching' at finer scales.