LATE PLEISTOCENE MAMMALS: BODY SIZE AND LOCAL COMMUNITY STRUCTURE

Body size distributions of modern mammals differ with spatial scale; continental faunas are right-skewed and highly modal, whereas local faunas are essentially uniform. Modal-sized species turn over more rapidly across space, while larger and smaller species occur repeatedly in different local faunas. Such patterns imply that body size mediated competition plays an important role in the structuring of local communities. Because there were considerable changes in the distributions of species, both terrestrial and marine, in response to the last glaciation cycle, the Late Pleistocene of North America is an ideal system with which to examine the role of body size in the structuring of local communities through time. I examined the body size distributions of local assemblages of mammals across the last 40000 yrs. Faunal lists for localities were taken from FAUNMAP along with the age and geographic position of the locality. Body size data were taken from a compilation by Smith et al., 2003. The distributions were evaluated for biases with respect to sampling and degree of time averaging. Localities with less than 20 species tended to cover a smaller range of body sizes and were eliminated from analyses. Data for modern localities were taken from Brown and Nicoletto (1991). Body size distributions of Late Pleistocene localities were compared to continental distributions and uniform distributions using Kolmorgorov-Smirnov two-sample tests. Because of the extinction of megafauna 10000 yra, the continental distribution used for comparison differed depending upon the age of the locality. A majority of the localities were significantly different from their continental distribution, and were not different from a uniform distribution. Given the considerable turnover in local community composition during the last glaciation, the similarity between the body size distributions of Late Pleistocene communities and modern communities implies that body size plays a key role in local community structure.

现生哺乳动物的体型分布随空间尺度呈现显著差异：大陆尺度动物群呈右偏态分布且具有鲜明的众数特征，而局域动物群的体型分布则基本趋近于均匀分布。体型处于众数区间的物种种间空间周转速率更快，而体型偏大或偏小的物种则在不同局域动物群中反复出现。上述分布格局表明，由体型介导的种间竞争在局域群落的结构构建中发挥着关键作用。
受末次冰期旋回（last glaciation cycle）影响，陆地与海洋物种的分布范围均发生了显著改变，因此北美晚更新世（Late Pleistocene）是探究体型随时间尺度如何调控局域群落结构构建的理想研究体系。本研究分析了过去4万年以来哺乳动物局域组合的体型分布特征。各地点的动物群名录及其年代与地理坐标数据均取自FAUNMAP数据库。体型数据则引自Smith等人2003年的汇编数据集。研究对体型分布是否存在采样偏差与时间平均效应偏差进行了系统性评估。物种数少于20的地点通常覆盖的体型范围较窄，因此被排除在本次分析之外。现代局域群落的体型分布数据引自Brown与Nicoletto1991年的研究成果。本研究采用柯尔莫哥洛夫-斯米尔诺夫双样本检验（Kolmogorov-Smirnov two-sample tests），将晚更新世各地点的体型分布与大陆尺度体型分布及均匀分布进行对比分析。由于1万年前巨型动物群（megafauna）的灭绝事件，用于对比的大陆尺度体型分布会依据各地点的年代不同进行相应调整。绝大多数研究地点的体型分布与对应大陆尺度的体型分布存在显著差异，但与均匀分布无显著区别。考虑到末次冰期期间局域群落组成发生了显著的物种周转，晚更新世群落与现代群落的体型分布存在相似性，这表明体型在局域群落结构构建中扮演着核心调控角色。