Spatial Ecology of American Bison on Vermejo Park Ranch, New Mexico

Authors

Kate Ann Asmus, University of Nebraska-LincolnFollow

First Advisor

John F. Benson

Committee Members

Carter G. Kruse, Larkin A. Powell, Daniel R. Uden

Date of this Version

12-2024

Document Type

Thesis

Citation

A thesis presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science

Major: Natural Resource Sciences

Under the supervision of Professor John F. Benson

Lincoln, Nebraska, December 2024

Comments

Copyright (c) 2024, Kate Ann Asmus. Used by permission

Abstract

American bison (Bison bison) are a keystone species that impact grassland productivity, plant diversity, and landscape heterogeneity. We used GPS telemetry and a replicate herbivore grazing experiment on Vermejo Park Ranch in northeastern New Mexico to advance understanding of bison spatial ecology and grazing dynamics. First, we evaluated the potentially disparate influences of forage productivity and site fidelity on the size and selection of home ranges of bison. Home range size was strongly negatively influenced by forage productivity. However, home range selection was influenced more strongly by site fidelity than spatial variation in forage, as bison selected home ranges with lower forage productivity relative to what was available across Vermejo. Second, we investigated whether collective grazing by bison in lower elevations modified plant growth to produce high-quality forage that released them from the need to migrate to higher elevations. Although forage productivity and graminoid quality were greater in higher elevations, bison in lower elevations maintained a diet of similar quality to bison translocated to higher elevations. Vegetation responded to ungulate grazing (mainly bison and elk) with equal or enhanced productivity in both years of our study, indicating that grazing levels likely improved (rather than degraded) ecosystem productivity. Third, we evaluated movement-based resource selection by bison during migratory-like travel. During these long-distance movements (mean = 19.0 km, range = 11.0 – 23.3 km), bison alternated between stationary, meandering, and directed movement states. Bison selected higher forage productivity in stationary and meandering states, whereas they avoided higher elevations and steeper slopes in the directed state. These results suggest an expanded perspective of stopover ecology that includes short-term shifts between directed travel and periods of foraging and rest whereby animals can alternatively prioritize optimal foraging and efficient travel during migration. Our work advances understanding of energetic tradeoffs between site fidelity and migration, the influence of grazing by large ungulates on ecosystem productivity, and behavioral strategies used by animals to fuel migration.

Advisor: John. F. Benson