Dustin H. Ranglack

Climate and density-dependent drivers of recruitment in plains bison

Abstract In semiarid ecosystems ungulate densities can compound the effects of drought on forage availability, which can feed back to regulate reproduction and offspring recruitment. Climatic changes in the frequency and severity of drought could thus exacerbate these effects. Here, we use long-term data sets to examine the dual influences of population density, cohort, and climatic variation on recruitment in the Henry Mountains bison (Bison bison bison) population. We found that 1-year lagged annual precipitation had a positive effect on recruitment (&bgr;  =  0.032, SE  =  0.009) and population density had a negative effect (&bgr;  =  −0.0023, SE  =  0.0004), but did not detect cohort effects. Furthermore, the effect of population density seemed to be more severe in dry relative to wet conditions, indicating that competition for forage could be severe in drought conditions. These results could help managers gain insight into the effects of climate change on bison population dynamics, and help guide the management of bison abundance on rangelands shared with cattle.

Competition on the range: science vs, perception in a bison-cattle conflict in the western USA

Summary Competition between livestock and wild ungulates is commonly perceived to occur on shared rangelands. 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. Bison are the most conspicuous potential competitors with cattle, but lagomorphs (mainly jackrabbits Lepus californicus) are also abundant in this area. The local ranching community is applying political pressure on state and federal agencies to resolve ‘the bison problem’, but the relative grazing impacts of bison, cattle and lagomorphs have not previously been quantified. We constructed 40 grazing exclosures (each 5·95 m2) in the conflict area: 20 excluded bison + cattle (‘partial’) and 20 excluded bison + cattle + lagomorphs (‘full’). All exclosures, each with a paired open reference plot, were monitored for 1 year, and above‐ground plant production was measured. GPS 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 recorded in a questionnaire survey. Ranchers perceived bison as a high‐level competitor with cattle, whereas lagomorphs were perceived as low‐level competitors. Grazed reference plots yielded an average (±SE) of 22·7 g m−2 (±5·16) of grass, compared to 36·5 g m−2 (±7·33) in the partial exclosures and 43·7 g m−2 (±7·61) in the full exclosures. Exclusion of large herbivores 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 13·7% and cattle 52·3% of the total grass biomass removed by all herbivores on the shared range. Synthesis and applications. Cattle face a greater competitive challenge from lagomorphs than from bison in the study area. This case study illustrates the need for science‐based management of social–ecological systems in which even long‐term resource users might underestimate the complexities of trophic interactions. Attention should be redirected at the lagomorphs and their main predators, coyotes Canis latrans, which are currently subject to population control. To reduce negative perceptions among local ranchers, options should be explored to incorporate benefit‐sharing into the management of the bison population.

Habitat Selection by Free-Ranging Bison in a Mixed Grazing System on Public Land☆

ABSTRACT Domestic livestock have replaced bison (Bison bison) on almost all the remaining rangelands of North America. One of the few places where bison and cattle (Bos taurus) comingle on shared rangelands is in the Henry Mountains (HM) of southern Utah. Ranchers there are concerned, however, that bison are selecting the same grazing areas that are needed by cattle. We used global positioning system telemetry on bison across the entire HM rangeland to determine which habitats are most important for bison throughout the seasonal cycle. Sexual segregation was also measured (using the segregation coefficient, SC) to determine if bison bulls exert localized impacts by congregating in certain habitats separate from cow/calf groups. The HM bison exhibited low levels of sexual segregation for both the breeding (SC = 0.048) and nonbreeding seasons (SC = 0.112). We found bison habitat use to be diverse and dynamic, with bison grazing effects distributed widely across habitats throughout the seasonal cycle. Patches of grassland, whether naturally occurring or created through burning or mechanical treatments, were favored regardless of their distance to water. Our findings should assist ranchers and agency personnel in moving forward with the integrated management of free-ranging bison and cattle on the HM rangeland, with implications for bison conservation on public lands elsewhere in the United States.

Bison with benefits: towards integrating wildlife and ranching sectors on a public rangeland in the western USA

The North American model of wildlife conservation, based on the public trust doctrine, is credited for the recovery of several charismatic wildlife species, including the plains bison Bison bison . In that model, wildlife is a public resource from which the private sector may not profit either individually or collectively. In recent years, however, resilience thinking is driving changes in the traditional state-run wildlife management model to allow for integrated multi-sector approaches at the landscape scale. A free-ranging herd of bison on public land in the Henry Mountains of Utah is used as a case study to consider if and how a community-based conservation programme could be developed for a state-managed wildlife resource to benefit all stakeholders. The Henry Mountains bison, which are disease-free, share the rangeland with cattle that are privately owned by individual ranchers and corporations with various economic goals and environmental values. The ranchers currently derive no benefits from the bison and have concerns regarding competition between bison and cattle. However, a threshold harvesting strategy with community participation could generate revenue to offset these concerns. It could also provide benefits to the local community, increase state revenue, and increase the size of the bison population while securing its long-term genetic viability. Implementation would initially require facilitation by policy specialists, after which we suggest a Henry Mountains bison partnership could serve as a model for bison recovery efforts elsewhere in North America.

Genetic Analysis of the Henry Mountains Bison Herd

Wild American plains bison (Bison bison) populations virtually disappeared in the late 1800s, with some remnant animals retained in what would become Yellowstone National Park and on private ranches. Some of these private bison were intentionally crossbred with cattle for commercial purposes. This forced hybridization resulted in both mitochondrial and nuclear introgression of cattle genes into some of the extant bison genome. As the private populations grew, excess animals, along with their history of cattle genetics, provided founders for newly established public bison populations. Of the US public bison herds, only those in Yellowstone and Wind Cave National Parks (YNP and WCNP) appear to be free of detectable levels of cattle introgression. However, a small free-ranging population (~350 animals) exists on public land, along with domestic cattle, in the Henry Mountains (HM) of southern Utah. This isolated bison herd originated from a founder group translocated from YNP in the 1940s. Using genetic samples from 129 individuals, we examined the genetic status of the HM population and found no evidence of mitochondrial or nuclear introgression of cattle genes. This new information confirms it is highly unlikely for free-living bison to crossbreed with cattle, and this disease-free HM bison herd is valuable for the long-term conservation of the species. This bison herd is a subpopulation of the YNP/WCNP/HM metapopulation, within which it can contribute significantly to national efforts to restore the American plains bison to more of its native range.

Considerations of context and scale when using fecal glucocorticoids to indicate stress in large mammals: a study of wild American plains bison

Abstract— Noninvasive measures of stress response are used to understand impacts of natural and anthropogenic disturbances on wild animals and can be challenging to interpret without additional contextual information and specifics of the animals in question. We used fecal samples collected from the Henry Mountains American plains bison (Bison bison) herd in Utah to measure the glucocorticoid hormone corticosterone (CORT), a hormone that is indicative of stress. We compared site-specific measures of fecal CORT concentration with measures of covariates related to geography, bison physiology, and human activity to determine whether an unexpected habitat selection pattern could be a response to human disturbance and thus whether ecological covariates could explain variations in fecal CORT concentration in free-ranging bison. No meaningful relationships were found for any of the covariates included in the study, in part due to a scale mismatch between the physiological stress response of bison and the spatiotemporal distribution of fresh feces deposited.