The relationship between body size and temperature of mammals is poorly resolved, especially for large keystone species such as bison (Bison bison).Bisonare well represented in the fossil record across North America, which provides an opportunity to relate body size to climate within a species. We measured the length of a leg bone (calcaneal tuber, DstL) in 849 specimens from 60 localities that were dated by stratigraphy and¹⁴C decay. We estimated body mass (M) asM = (DstL/11.49)³. Average annual temperature was estimated from δ¹⁸O values in the ice cores from Greenland. Calcaneal tuber length of Bison declined over the last 40,000 years, that is, average body mass was 37% larger (910 ± 50 kg) than today (665 ± 21 kg). Average annual temperature has warmed by 6°C since the Last Glacial Maximum (~24–18 kya) and is predicted to further increase by 4°C by the end of the 21st century. If body size continues to linearly respond to global temperature,Bisonbody mass will likely decline by an additional 46%, to 357 ± 54 kg, with an increase of 4°C globally. The rate of mass loss is 41 ± 10 kg per°C increase in global temperature. Changes in body size ofBisonmay be a result of migration, disease, or human harvest but those effects are likely to be local and short‐term and not likely to persist over the long time scale of the fossil record. The strong correspondence between body size of bison and air temperature is more likely the result of persistent effects on the ability to grow and the consequences of sustaining a large body mass in a warming environment. Continuing rises in global temperature will likely depress body sizes of bison, and perhaps other large grazers, without human intervention.

Future climate projections of warming, drying, and increased weather variability indicate that conventional agricultural and production practices within the Northern Great Plains (NGP) will become less sustainable, both ecologically and economically. As a result, the livelihoods of people that rely on these lands will be adversely impacted. This is especially true for Native American communities, who were relegated to reservations where the land is often vast but marginal and non-tribal operators have an outsized role in food production. In addition, NGP lands are expected to warm and dry disproportionately relative to the rest of the United States. It is therefore critical to identify models of sustainable land management that can improve ecological function and socio-economic outcomes for NGP communities, all while increasing resilience to a rapidly changing climate. Efforts led by Native American Nations to restore North American Plains bison (Bison bison bison) to tribal lands can bring desired socio-ecological benefits to underserved communities while improving their capacity to influence the health of their lands, their people, and their livelihoods. Ecological sustainability will depend on the restoration of bison herds and bison’s ability to serve as ecosystem engineers of North America’s Plains. The historically broad distribution of bison suggests they can adapt to a variety of conditions, making them resilient to a wide range of management systems and climates. Here we review bison’s ecological, cultural, and economic value using four case studies from tribal communities within the NGP. We discuss the potential contributions of bison to food sovereignty, sustainable economies, and conservation of a working landscape with limited protections and significant risk of conversion. The ecological role of bison within this setting has potential due to cultural acceptance and the vast availability of suitable lands; however, it is critical to address tribal needs for funding support, enhanced community capacity, and solving complex landownership for these goals to be achieved.

Bison Bison bison are a keystone of a conservation system, but that system is vulnerable to the effects of a changing climate projected to alter land use through the 21st century. The current bison population of North America is approximately 400,000 animals and is maintained by a self‐assembled bison management system (BMS) of various stakeholders focused on bison conservation and production. The BMS is comprised of public, for‐profit private, Tribal and not‐for‐profit non‐governmental organization (NGO) sectors, with complementary values, attitudes and practices that contribute to a robust conservation footprint for the species. Currently, the majority of grasslands (90%) and bison (85%) are privately owned which justifies the need for robust private land conservation strategies to maintain this iconic species and its grassland habitats. We assessed vulnerability of the BMS to 21st century consequences of climate change with a vulnerability scoping diagram that emphasizes exposure, sensitivity and adaptive capacity, as well as environmental values, attitudes and practices. We surveyed 132 bison managers within both the private and public/NGO sectors. Respondents were predominantly educated white males located in the northern and central mixed grass prairies who manage bison herds of, on average, 51–100 animals. Overall, the BMS is moderately vulnerable to climate change. While the public/NGO and private sectors differ in adaptive capacity, specifically in measures of information exchange, external revenue, use of management plans and access to grazing leases, the sectors act as partners for exchanging bison and rely on sustained interchange of bison; dimensions of exposure and sensitivity appear similar between public/NGO and private sectors. The complementary, shared environmental values and attitudes of the private and public/NGO sectors shape the foundation for enhanced collaboration among the multi‐sector BMS. But it is the sharing of diverse practices and respective consequences that will lead the BMS to discover credible, scalable adaptive solutions to climate change. This may lead to the bison community to decide whether to form a ‘bison coalition’ to seek solutions to adapt to climate change. A free Plain Language Summary can be found within the Supporting Information of this article.

Large grazers are visible and valuable indicators of the effects of projected changes in temperature and drought on grasslands. The grasslands of the Great Plains have supported the greatest number of bison (Bison bison; Linnaeus, 1758) since prehistoric times. We tested the hypothesis that body mass (BM, kg) and asymptotic body mass (ABM, kg) of Bison decline with rising temperature and increasing drought over both temporal and spatial scales along the Great Plains. Temporally, we modeled the relationship of annual measures of BM and height (H, m) of 5,781 Bison at Wind Cave National Park (WICA) from 1966 to 2015. We used Gompertz equations of BM against age to estimate ABM in decadal cohorts; both females and males decreased from the 1960s to the 2010s. Male ABM was variable but consistently larger (699 vs. 441 kg) than female ABM. We used local mean decadal temperature (MDT) and local mean decadal Palmer Drought Severity Index (dPDSI) to model the effects of climate on ABM. Drought decreased ABM temporally (−16 kg/local dPDSI) at WICA. Spatially, we used photogrammetry to measure body height (H_E) of 773 Bison to estimate BM_E in 19 herds from Saskatchewan to Texas, including WICA. Drought also decreased ABM spatially (−16 kg/local dPDSI) along the Great Plains. Temperature decreased ABM both temporally at WICA (−115 kg/°C local MDT) and spatially (−1 kg/°C local MDT) along the Great Plains. Our data indicate that temperature and drought drive Bison ABM presumably by affecting seasonal mass gain. Bison body size is likely to decline over the next five decades throughout the Great Plains due to projected increases in temperatures and both the frequency and intensity of drought.

Body size of bison (Bison bison) declines with rising global temperature across the fossil record and rising annual temperatures across the Great Plains, but what are the underlying drivers? Body size depends on growth, which depends on maximizing net energy and nutrient flows for the production of tissues at seasonal scales across the range of the species. We measured thermoregulation costs of body surface temperature (°C) and heat exchanges (W and W/m²) of 350 adult and 345 adolescentBisonfrom 19 herds in summer and winter along the Great Plains from Saskatchewan (52° N) to Texas (30° N). At the smallest scale, daily body surface temperature increased with solar radiation and decreased with relative humidity and wind speed, which is consistent with Kooijman’s dynamic energy budget theory. Total surface heat transfer (W) increased with body mass (kg) at an exponent of 0.63 ± 0.03, which is consistent with Schmidt‐Nielsen’s principle of surface‐area‐to‐volume ratios (b = 0.67). On an annual scale, growth (kg/yr) of adolescentBisondecreased with increasing total surface heat transfer (W) during summer, which supports Speakman and Król’s heat dissipation limit theory. On the largest scale, heat flux was weakly related to latitude in summer and winter for adolescentBison, which provides support for Bergmann’s rule and suggests a role for local primary production along the Great Plains. Cooler summers are more optimal forBisongrowth because of reduced heat loads during the growing season. Rising temperatures are likely to constrain body size and productivity ofBisonand other large endotherms in North America.