Early Occupations in Bighorn Canyon,Montana

Abstract

Excavation of the Mangus Site (24CB22l) in Bighorn Canyon, Montana revealed a stratum containing artifacts of the Agate Basin Complex. This occupation was dated by radiocarbon at 6740 B. C. and 6650 B. C. The Sorenson Site (24CB202) contained two early cultural levels, one of unknown cultural affiliation datedat 5850 B. C. and 5610 B. C. overlying a second unidentified occupation. Future investigations in Bighorn Canyon may produce artifacts allowing identification of these two occupations.     

Historic variability in fire‐generated landscape heterogeneity of subalpine forests in the Canadian Rockies

Question: This study evaluates historical changes in landscape structure and heterogeneity in subalpine forests. We use response to severe fires in 2001 and 2003, along with historical reconstructions to examine crown‐fire effects on landscape heterogeneity and to assess, comparatively, effects of fire exclusion management in the 20th century. Location: Subalpine forests of Kootenay National Park (KNP), Canadian Rockies. Methods: Using a landscape‐level model based on a fire‐origin stand age map, we reconstructed decadal burned areas within the landscape for 1750‐2000 (forming reconstructed landscapes). Landscape pattern was analysed for each reconstructed landscape map, and we compared landscape pattern indices (total area, number of patches, mean patch area, patch area variation, largest patch index, edge density, perimeter–area ratio, landscape shape index) with those in 2005 after recent large fires. Results: After large fires in 1926, connectivity of the KNP landscape increased and its diversity was quite low. After 2001 and 2003 fires, the post‐fire landscape of 2005 was highly heterogeneous in terms of size, variation, edge density and perimeter–area ratio of the remnant forest patches. Since the decline in occurrence of large fires after 1926 reflected a period of wet weather, fuel build‐up resulting from landscape homogenization within the 20th century landscape could not be attributed solely to fire exclusion. This period without fires greatly enhanced connectivity of late‐successional forests that finally burned in 2001/2003, but connectivity was within the historical range for these forests. The gradual increase in stand connectivity before recent large fires may indicate that fire exclusion was less responsible than often believed for fuel build‐up in these fire‐susceptible older forests. Conclusions: The large fires at the beginning of the 21st century are within the natural range of disturbances for this landscape, and do not stand out as “human‐induced disasters” in their effects on landscape patterns. Such stochastic large disturbances contribute to maintenance of highly heterogeneous landscape structure, which is important for many taxa and natural ecological processes. Identifying future probability of such large disturbances and their ecological roles should be incorporated into management of these dynamic, disturbance‐prone systems.     

Epizootic Pneumonia of Bighorn Sheep following Experimental Exposure to Mycoplasma ovipneumoniae

Background

Bronchopneumonia is a population limiting disease of bighorn sheep (Ovis canadensis). The cause of this disease has been a subject of debate. Leukotoxin expressing Mannheimia haemolytica and Bibersteinia trehalosi produce acute pneumonia after experimental challenge but are infrequently isolated from animals in natural outbreaks. Mycoplasma ovipneumoniae, epidemiologically implicated in naturally occurring outbreaks, has received little experimental evaluation as a primary agent of bighorn sheep pneumonia.

Methodology/Principal Findings

In two experiments, bighorn sheep housed in multiple pens 7.6 to 12 m apart were exposed to M. ovipneumoniae by introduction of a single infected or challenged animal to a single pen. Respiratory disease was monitored by observation of clinical signs and confirmed by necropsy. Bacterial involvement in the pneumonic lungs was evaluated by conventional aerobic bacteriology and by culture-independent methods. In both experiments the challenge strain of M. ovipneumoniae was transmitted to all animals both within and between pens and all infected bighorn sheep developed bronchopneumonia. In six bighorn sheep in which the disease was allowed to run its course, three died with bronchopneumonia 34, 65, and 109 days after M. ovipneumoniae introduction. Diverse bacterial populations, predominantly including multiple obligate anaerobic species, were present in pneumonic lung tissues at necropsy.

Conclusions/Significance

Exposure to a single M. ovipneumoniae infected animal resulted in transmission of infection to all bighorn sheep both within the pen and in adjacent pens, and all infected sheep developed bronchopneumonia. The epidemiologic, pathologic and microbiologic findings in these experimental animals resembled those seen in naturally occurring pneumonia outbreaks in free ranging bighorn sheep.     

Genetic Variation of Major Histocompatibility Complex and Microsatellite Loci: A Comparison in Bighorn Sheep

Examining and comparing genetic variation for major histocompatibility complex (MHC) and microsatellite (MS) loci in the same individuals provides an opportunity to understand the forces influencing genetic variation. We examined five MHC and three MS loci in 235 bighorn sheep (Ovis canadensis) from 14 populations and found that both types of loci were highly variable and were in Hardy-Weinberg proportions. Mean F(ST) values for both markers were very similar and MHC and MS genetic variability was predominantly distributed within rather than among populations. However, analyses of genetic distances and tree topologies revealed different spatial patterns of variation for the two types of loci. Collectively, these results indicated that neutral forces substantially influenced MS and MHC variation, and they provided limited evidence for selection acting on the MHC.     

Molecular helminthology in the Rockies

A report on the Keystone Symposium on Molecular Helminthology, Copper Mountain, Colorado, USA, 9-13 April 2005.     

Rut-Induced Hypophagia in Male Bighorn Sheep and Mountain Goats: Foraging Under Time Budget Constraints

In polygynous ungulates, the rut imposes constraints on male time budgets that generate a trade‐off between maintenance and reproduction, leading to a reduction in time spent foraging. As mating activities can incur substantial somatic costs, males are expected to spend their ‘non‐rutting’ time recovering during the breeding season. If the diminution in time allocated to foraging by males is only a consequence of time budget constraints, males should keep a similar ratio of time spent foraging to lying to that observed in the pre‐rut, leading to an overall reduction of these two activities (the ‘foraging constraint’ hypothesis). Alternatively, if males adopt an energy‐saving strategy, they should limit energy expenditures by reducing foraging but not lying time, as the energy gains of forage intake may not meet the basal energetic requirements, especially in northern and temperate regions (the ‘energy‐saving’ hypothesis). Here, we contrast these two hypotheses by comparing individual daily time budgets of marked adult bighorn sheep rams (Ovis canadensis) and male mountain goats (Oreamnos americanus) during the pre‐rut and the rut. Concordant results for both species support the ‘foraging constraint’ hypothesis, as sexually‐active males reduced time spent foraging and lying from the pre‐rut to the rut because of an increase in time spent in mating‐related activities. Bighorn sheep rams also increased time spent foraging when not engaged in mating tactics, providing further support for a ‘maximisation’ of energy intake in the absence of reproductive opportunities. Because there are also known physiological changes that occur during the rut which may cause appetite suppression, for example to produce metabolic compounds linked with olfactory communication (the ‘scent‐urination’ hypothesis) or to cope with increased burden of parasites (the ‘parasite‐induced anorexia’ hypothesis), further research should aim at simultaneously testing these current hypotheses to better understand rut‐induced hypophagia and its effects on the life histories of male ungulates.     

Weaning Conflict in Desert and Mountain Bighorn Sheep (Ovis canadensis): An Ecological Interpretation

Field data on weaning behavior in bighorn sheep (Ovis canadensis) were collected from populations in British Columbia, southern California, and one transplanted from the original B.C. study site to eastern Oregon. These areas were designated mountain, desert, and transplant, respectively. Seasons that were energetically stressful to lactating ewes were predicted. Summers were implicated for desert ewes; winters for ewes in colder and more seasonal northern environments. Although the temporal distribution of milk available to lambs varied between the three study populations, ewes generally weaned their lambs prior to the onset of the predicted stressful periods. In the desert, weaning occurred more abruptly than it did in the two more northern populations. The evolution of weaning strategies is discussed in subspecies of bighorn sheep based on proximate and ultimate factors.