Spatial ecology of North American bison on Vermejo, New Mexico
Principle Investigators
Dr. John Benson, University of Nebraska - Lincoln, School of Natural Resources
Dr. Carter Kruse – Turner Institute of Ecoagriculture
Dr. Dustin Ranglack – USDA National Wildlife Research Center
Graduate Student
Kate Asmus, University of Nebraska - Lincoln
Rationale.
North American bison are often considered a keystone species due to their influence on species composition, alteration of the physical and chemical environment, and impact on spatial and temporal landscape heterogeneity. Bison do not graze in a uniform manner, instead they create both distinct grazing patches and large grazing lawns. Through these distinct grazing patterns, bison enhance forage quality and maintain landscape heterogeneity both at small- and large-scales. On Vermejo, we intend to analyze movement decisions by North American bison to better understand the primary drivers of their local distribution and grazing behavior. This study will evaluate factors that influence the size and selection of home ranges for bison on Vermejo, and the role these factors play on space use patterns; whether aggregate grazing behavior results in high-quality forage patches that free bison from the costs of migration and whether movement decisions are timed with the emergence of green-up in spring; and finally, an assessment of overall landscape connectivity to identify movement corridors used by bison to move between habitat at high and low elevation. Addressing these questions will inform local management decision on Vermejo, provide a better understanding of bison ecology in the American Southwest, and contribute more broadly to important ecological concepts such as second-order habitat selection, the green wave hypothesis, and landscape connectivity.
Outcomes.
Outcomes. Bison home range at Vermejo 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. 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. During long distance movements (range 11-23 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.
Asmus, K.A. 2024. Spatial ecology of American bison on Vermejo Park Ranch, New Mexico. M.S. Thesis. University of Nebraska, Lincoln, NE.
Asmus, K.A., C.G. Kruse, D.H. Ranglack and J.F. Benson. In press. Drivers of spatial dynamics of a large ungulate (American Bison, Bos bison): forage productivity or site fidelity? Journal of Mammalogy
