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...哺乳动物体型与体温之间的关联迄今尚未得到清晰阐释，对于美洲野牛（Bison bison）这类大型关键物种而言尤为如此。北美各地的化石记录中均有大量野牛化石留存，这为探究同一物种的体型与气候之间的关联提供了契机。我们对来自60个遗址的849件标本的腿骨（跟骨结节，calcaneal tuber，记为DstL）长度进行了测量，这些标本的年代通过地层学与碳十四（¹⁴C）衰变法确定。我们通过以下公式估算体质量（M）：M = (DstL/11.49)³。年平均气温通过格陵兰冰芯中的氧同位素δ¹⁸O值估算得到。过去4万年以来，野牛的跟骨结节长度呈下降趋势，即其平均体质量（910 ± 50 kg）较现今（665 ± 21 kg）高出37%。自末次冰盛期（Last Glacial Maximum，约2.4万至1.8万年前）以来，年平均气温已上升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响应变化，则野牛的体质量大概率会继续下降……