Competition on the range: science versus perception in bison-cattle-jackrabbit interactions on public land
Competition between livestock and wild ungulates is commonly perceived to occur on shared rangelands but is seldom tested for. In the Henry Mountains (HM) of Utah a free-ranging population of bison (Bison bison) has raised concerns among ranchers holding grazing permits on these public lands. While bison are the most conspicuous potential competitors with cattle, lagomorphs (mainly jackrabbits, Lepus californicus) are abundant in the area due to intensive coyote (Canis latrans) removal efforts by state and federal agencies, as well as private individuals. The local ranching community is applying political pressure on state and federal agencies to resolve the “bison problem”, but the relative impacts of bison, cattle, and lagomorphs are unknown. Forty grazing exclosures (each 5.95 m2) were constructed in the conflict area, of which 20 excluded bison + cattle (partial) and 20 excluded bison + cattle + lagomorphs (full). All exclosures, each with an open reference plot, were monitored for one year and vegetation production was measured by clipping and weighing. Telemetry (bison) and scheduled grazing (cattle) allowed visitation to be quantified for each ungulate species based on the number of “animal days” in the area. Rancher perceptions of wildlife-cattle interactions were captured in a questionnaire survey.
Ranchers perceived bison as a medium to medium-high competitor with cattle while lagomorphs were consistently perceived as a low-level competitor. Reference plots yielded an average of 22.7 g m-2 (SE = 5.16) of grass, compared to 36.5 g m-2 (SE = 7.33) in the partial exclosure and 43.7 g m-2 (SE = 7.61) in the full exclosure. Exclusion of bison + cattle thus resulted in a 13.8 g m-2 increase in grass biomass relative to the reference plots (p = 0.005), with the additional exclusion of lagomorphs resulting in a further 7.18 g m-2 increase (p = 0.048). Overall, lagomorphs accounted for 34.1%, bison 12.6-29.3% and cattle 36.6–53.4% of the total grass biomass removed by all herbivores on the shared range. Exclosures and reference plots did not differ with respect to forb, cactus, and shrub biomass. We conclude that cattle face a greater competitive challenge from lagomorphs than from bison on the HM range and coyote control efforts should be reconsidered. This case-study illustrates the need for science-based management of social-ecological systems in which even long-term resource users might under-estimate the complexities of trophic cascades.