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迄今尚未得到充分厘清，对于野牛（Bison bison）这类大型关键物种而言尤其如此。北美地区的化石记录中野牛遗存极为丰富，这为探究同一物种种群体型与气候之间的关联提供了契机。 我们对来自60个地层位点、经地层学与碳十四（14C）衰变测年的849件标本的腿骨（跟骨结节，calcaneal tuber，缩写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。 年均温则通过格陵兰冰芯的δ¹⁸O值估算得到。研究发现，过去4万年间野牛的跟骨结节长度持续下降，其彼时平均体质量达910 ± 50 kg，较当代野牛的665 ± 21 kg高出37%。 自末次冰盛期（Last Glacial Maximum，约2.4万~1.8万年前）以来，全球年均温已上升6℃，且据预测，到21世纪末还将进一步升高4℃。若体质量仍随全球温度呈线性响应，则随着全球升温4℃，野牛的体质量将再下降46%，降至357 ± 54 kg；全球温度每升高1℃，野牛体质量将减少41 ± 10 kg。 野牛体型的变化可能与迁徙、疾病或人类狩猎有关，但这些影响多为局地性且短期的，难以在化石记录所覆盖的长期时间尺度上持续存在。野牛体型与气温间的强相关性，更可能源于升温环境下，个体生长能力受到的长期持续影响，以及维持大体质量所带来的一系列生理代价。 若无人类干预，全球温度的持续上升或将进一步压低野牛乃至其他大型植食动物的体型。