Document Type

Thesis - Open Access

Award Date

2026

Degree Name

Master of Science (MS)

Department / School

Natural Resource Management

First Advisor

William Severud

Abstract

Respiratory disease caused by Mycoplasma ovipneumoniae is among the most significant threats to bighorn sheep (Ovis canadensis) conservation in North America. In July 2021, contact between bighorn sheep rams and domestic sheep north of Badlands National Park (BADL), South Dakota, USA introduced M. ovipneumoniae into the Badlands bighorn sheep meta-population, triggering an epizootic that reduced the population by approximately 80%. I evaluated the post-outbreak status of this population through two complementary studies conducted from 2023 to 2025. In Chapter 1, I quantified disease prevalence, adult survival, lamb recruitment, and population growth rate (λ) using serial quantitative polymerase chain reaction (qPCR) testing, staggered-entry Kaplan- Meier survival analysis, and Leslie matrix projection models. qPCR prevalence was 29.5% in 2023 (n = 44) and 28.6% in 2024 (n = 42). Adult survival was high and stable (female Ŝ = 0.92–0.93; male Ŝ = 0.84–0.94), but apparent lamb survival remained suppressed at 18–21%, well below pre-outbreak levels of 82%. Population growth rate was below replacement in both intervals (λ = 0.933–0.937), and the population declined to a minimum count of 43 individuals by March 2025. These results indicated a transition from acute epizootic to chronic endemic disease, with continued population decline driven by suppressed lamb recruitment rather than adult mortality. In Chapter 2, I used step-selection functions fit to GPS data from 18 collared rams (33,203 fixes) to identify landscape drivers of ram movement and predict areas of elevated M. ovipneumoniae spillover risk. Rams selected for higher elevations, rugged terrain, and areas away from anthropogenic landcover across all three seasons (Breeding, Lambing, Non-Breeding). Breeding season produced the most frequent forays from core ranges, but Non-Breeding forays were longer in duration and reached greater maximum displacements, suggesting elevated perevent contact risk outside of the rut. Movement suitability and contact risk surfaces identified the Pinnacles area of BADL as the zone of consistently highest predicted spillover risk. These findings provide a demographic and spatial framework for managing M. ovipneumoniae in the Badlands metapopulation and prioritizing monitoring and outreach efforts to prevent future pathogen introductions.

Publisher

South Dakota State University

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