Data from: Lean-season primary productivity and heat dissipation as key drivers of geographic body-size variation in a widespread marsupial

Geographic body-size variation characterises many mammal species. Hypotheses centring around heat conservation, heat dissipation, primary productivity and seasonality have been advanced to explain geographic body-size patterns. However, identification of the primary body-size drivers has often been hampered by a paucity of data for broadly distributed species and the application of regression models that have not explicitly accounted for the spatial clustering inherent in such datasets. We used Australia's most widespread marsupial, the common brushtail possum Trichosurus vulpecula, as a model species with which to test five proposed drivers of geographic body-size variation. Using geo-referenced skull measurements from 588 specimens and a suite of putative environmental covariates, we employed spatial simultaneous autoregressive models, together with information criteria, to evaluate these different hypotheses. Our analysis identified a strong, positive relationship between possum body size and primary productivity during the least productive season, whereas the relationship with mean annual productivity received less support. Consistent with the heat-dissipation hypothesis, T. vulpecula body size also decreased with increasing mean summer maximum temperature. Spatial autoregression coefficients estimated from the simultaneous autoregressive models were always high, suggesting that additional abiotic or biotic factors might contribute to the spatial patterns observed. We argue that the analysis of geographic body-size variation should consider multi-causal possibilities rather than treating the numerous hypotheses as competing, mutually exclusive alternatives.

许多哺乳动物类群均呈现出地理体型变异的特征。围绕体温保存（heat conservation）、热量散失（heat dissipation）、初级生产力（primary productivity）以及季节节律提出的诸多假说，已被用于解释地理体型格局的形成机制。然而，广布物种的数据匮乏，以及未明确考量此类数据集固有空间聚类特征的回归模型应用，往往阻碍了对体型主要驱动因子的识别。本研究以澳大利亚分布最广的有袋类动物——刷尾负鼠（common brushtail possum, Trichosurus vulpecula）作为模式物种，对5种已被提出的地理体型变异驱动因子开展检验。研究借助588号标本的地理参考（geo-referenced）头骨测量数据，以及一系列假定的环境协变量，结合空间同时自回归模型（spatial simultaneous autoregressive models）与信息准则（information criteria），对上述不同假说进行评估。分析结果显示，刷尾负鼠的体型与最低产季的初级生产力之间存在显著正相关关系，而与年平均初级生产力的关联则未获得足够支持。契合热量散失假说（heat-dissipation hypothesis）的预测，刷尾负鼠的体型会随夏季平均最高气温的升高而减小。从同时自回归模型中估算得到的空间自回归系数始终较高，这表明除已考虑的因子外，尚有其他非生物或生物因子可能对观测到的空间格局产生影响。本研究认为，在开展地理体型变异相关分析时，应考虑多因子共同作用的可能性，而非将诸多假说视为相互竞争、互斥的选项。