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.诸多哺乳动物类群均存在地理体型变异现象。围绕热量留存（heat conservation）、热量散失（heat dissipation）、初级生产力（primary productivity）与季节性（seasonality）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，针对广泛分布物种种群的基础数据匮乏，且过往回归模型未明确考虑此类数据集固有的空间聚类（spatial clustering）特征，这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（marsupial）动物——刷尾负鼠（Trichosurus vulpecula）为模式物种，对5种已被提出的地理体型变异驱动因子进行检验。本研究利用588号标本的地理定位（geo-referenced）头骨测量数据，以及一系列假定环境协变量（putative environmental covariates），结合信息准则（information criteria），采用空间同时自回归模型（spatial simultaneous autoregressive models）对上述不同假说进行评估。分析结果显示，负鼠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得到有力支持。符合热量散失假说（heat-dissipation hypothesis）的预测，刷尾负鼠的体型亦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，这表明额外的非生物（abiotic）或生物（biotic）因子可能对观测到的空间格局存在贡献。本研究认为，在开展地理体型变异分析时，应考虑多因果可能性，而非将众多假说视为相互竞争、互斥的选项。