Date of Award

5-2026

Degree Type

Thesis

Degree Name

Departmental Honors

Department

Wildland Resources

Abstract

Elk (Cervus elaphus) in Yellowstone National Park exist within a predator-prey system shaped by long-term interactions with wolves (Canis lupus). This predator-prey system represents an important model for understanding how predation influences ungulate behavior and social organization. Predators affect prey behavior through direct and indirect interactions and may cause long-term changes. What this study strives to answer is if predator success can have long term effects on prey grouping behavior and age-sex structure. In a previous study, wolves were found to be most successful hunting medium sized group of elk (20-49 individuals) in Yellowstone National Park. The goal of the present study is to assess the extent that wolf hunting success is a selective pressure on elk, shifting grouping behavior away from medium sized groups. Using long term aerial count data of elk, we looked at long term trends of elk grouping behavior inside and outside northern Yellowstone National Park. The study was conducted within the northern range, where predation pressure is higher inside the park and lower outside the park, enabling a direct comparison between high and low predation areas. Medium sized group frequencies declined sharply in both high and low predation areas. Very small (2-8 individuals) and small (9-19 individuals) groups increased both inside and outside the park. Very small groups increased sharply inside the park, and moderately outside the park. Very small groups increased more rapidly outside the park than inside the park. Large groups sharply decreased inside and moderately increased outside, and very large groups somewhat increased inside and decreased steeply outside the park. Increases in wolf hunting success for a given group size are typically associated with declines in the frequency of that group size inside the park over time. The age-sex structure also shifted with group sizes and location. These patterns are consistent with the hypothesis that elk avoided group sizes associated with elevated wolf predation risk. Wolf hunting success could be a strong selective pressure that changes elk grouping behavior, like group size and age-sex structure.

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Faculty Mentor

Daniel MacNulty

Departmental Honors Advisor

Kari Veblen