Date of Award:

5-2023

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Wildland Resources

Committee Chair(s)

Kezia Manlove

Committee

Kezia Manlove

Committee

Kathleen Longshore

Committee

Mary Conner

Committee

David Stoner

Abstract

Managers mitigate the effects of disease on wildlife populations by detecting outbreaks and predicting disease transmission. Bighorn sheep (Ovis canadensis) populations face threat from the introduced pathogen Mycoplasma ovipneumoniae (M. ovipneumoniae). In the eastern Mojave Desert, managers detect pathogen outbreaks in desert bighorn (O. c. nelsoni) through aerial population surveys, which produce irregular and coarse population information. Furthermore, managers model the risk of M. ovipneumoniae transmission amongst desert bighorn populations, however these models assume that desert bighorn space use is unchanging across years. Here, I evaluate methods used by managers to detect disease outbreaks and an assumption for predicting disease transmission. The results will provide managers guidance for passive vital rate monitoring and refine models informing managers of transmission risk.

In my second chapter, I evaluated camera traps’ ability to represent population metrics indicative of disease outbreak and persistence. I compared camera- and in personderived bighorn counts to quantify how well cameras detect presence, group sizes, and lamb:ewe ratios. Across camera trap sites and years examined, the probability that camera traps detected present bighorn sheep ranged from 44% to 100%, with per-minute probability ranging from 6% to 84%. The probability that camera traps detected the arrival of new groups ranged from 18% to 100%. Camera-derived group size estimates exhibited substantial negative bias across all sites and demographic groups, and bias varied across group sizes present. Across all sites, the multiplicative change between camera and observer lamb:ewe ratios ranged from 1.79 to 2.46.

In my third chapter, I evaluated the assumption that desert bighorn space use is consistent across years when environmental condition varies. I did this by examining how home range sizes varied as a function of dynamic environmental condition, including environmental moisture and plant biomass, and static landscape characteristics, including slope, vector ruggedness measure (VRM), and distance to water. I found that ram home range sizes responded more to temporally dynamic variables than ewe home ranges, while ewe home range sizes responded more to landscape features. These results suggest that transmission risk models should incorporate bighorn space use changes across years.

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