Data from: Bison body size and climate change

The relationship between body size and temperature of mammals is poorly resolved, especially for large keystone species such as bison (Bison bison). Bison are 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 and 14C decay. We estimated body mass (M) as: M = (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, Bison body 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 of global temperature. Changes in body size of Bison may 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.哺乳动物体型与温度之间的关联尚未得到清晰阐明，对于美洲野牛（Bison bison）这类大型关键物种而言尤其如此。美洲野牛在北美各地的化石记录中均有大量留存，这为探究同一物种内体型与气候的关联提供了契机。我们对来自60个经地层学与碳14衰变定年的遗址的849件标本的腿骨（跟骨结节，DstL）长度进行了测量。我们通过以下公式估算体质量（M）：M = (DstL/11.49)³。年均气温通过格陵兰岛冰芯中的δ¹⁸O值估算得到。过去4万年以来，美洲野牛的跟骨结节长度持续下降，即其平均体质量较现代（665 ± 21 kg）高出37%（910 ± 50 kg）。自末次冰盛期（约2.4万至1.8万年前）以来，全球年均气温已上升6℃，且预计到21世纪末将进一步升高4℃。若体型仍随全球气温呈线性变化，那么当全球气温再升高4℃时，美洲野牛的体质量预计将再下降46%，降至357 ± 54 kg。体质量的下降速率为每升高1℃全球气温，体质量减少41 ± 10 kg。美洲野牛体型的变化可能由迁徙、疾病或人类狩猎导致，但这些影响多局限于局部且具有短期性，难以在化石记录所代表的长期时间尺度上持续存在。美洲野牛体型与气温之间的显著关联，更可能源于变暖环境下对生长能力及维持大体质量的持续影响。若无人类干预，全球气温的持续上升可能会抑制美洲野牛乃至其他大型植食动物的体型增长。