Date of Award:

8-2023

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Wildland Resources

Committee Chair(s)

Simona Picardi

Committee

Simona Picardi

Committee

Tal Avgar

Committee

Garrett Street

Committee

Kari Veblen

Abstract

Large herbivores, such as mule deer and cattle have similar life histories and likely compete for resources. However, quantifying the extent to which these species compete and the specific resources they compete for has proved challenging. My research examines if cattle influence deer abundance and behavior due to competition for forage, competition for shade, and/or by affecting the predation risk of deer. Using a grid of autonomous trail cameras, I was able to determine if cattle abundance influences local deer abundance in relation to specific resources and habitat features. Using GPS data from collared deer, I was also able to examine if cattle density affects the probability that a deer was in a foraging, resting, or commuting state. I found evidence that cattle abundance reduces deer abundance in forage-rich areas, indicating that these species are likely competing for forage. Likewise, I found that cattle density increases the probability that a deer is foraging, and reduces the probability that a deer is commuting. Behavioral data is difficult to interpret, but this may suggest that deer must compensate for having less forage available due to competitors by spending more time foraging. However, it is also possible that cattle are merely an indicator of good habitat, so deer are more likely to forage in areas where cows are present. I did not find any compelling evidence of shade competition or predation risk effects between deer and cattle. My work demonstrates that it is important to examine many different data sources when trying to assess competition between large herbivores, and to not just assume what resources are driving competition. Additionally, my work demonstrated that forage competition occurs between mule deer and cattle, so managers should take this into account when balancing their goals for livestock, mule deer, and rangeland health.

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