Data from: Empirical tests of harvest-induced body-size evolution along a geographic gradient in Australian macropods

1. Life-history theory predicts the progressive dwarfing of animal populations that are subjected to chronic mortality stress but the evolutionary impact of harvesting terrestrial herbivores has seldom been tested. In Australia, marsupials of the genus Macropus (kangaroos and wallabies) are subjected to size-selective commercial harvesting. Mathematical modelling suggests that harvest quotas (ca. 10–20 % of population estimates annually) could be driving body-size evolution in these species. 2. We tested this hypothesis for three harvested macropod species with continental-scale distributions. To do so, we measured more than 2 000 macropod skulls sourced from wildlife collections spanning the last 130 years. We analysed these data using spatial Bayesian models that controlled for the age and sex of specimens as well as environmental drivers and island effects. 3. We found no evidence for the hypothesized decline in body size for any species; rather, models that fit trend terms supported minor body size increases over time. This apparently counterintuitive result is consistent with reduced mortality due to a depauperate predator guild and increased primary productivity of grassland vegetation following European settlement in Australia. 4. Spatial patterns in macropod body size supported the heat dissipation limit and productivity hypotheses proposed to explain geographic body-size variation (i.e., skull size increased with decreasing summer maximum temperature and increasing rainfall, respectively). 5. There is no empirical evidence that size-selective harvesting has driven the evolution of smaller body size in Australian macropods. Bayesian models are appropriate for investigating the long-term impact of human harvesting because they can impute missing data, fit non-linear growth models and account for non-random spatial sampling inherent in wildlife collections.

1. 生活史理论（Life-history theory）预测，长期经受慢性死亡压力的动物种群会逐渐出现体型小型化，但陆地植食性动物狩猎的进化影响却极少被验证。在澳大利亚，大袋鼠属（Macropus）的有袋类（袋鼠和沙袋鼠）面临体型选择性商业狩猎。数学模型显示，狩猎配额（约为年度种群估算量的10%~20%）可能正在推动这些物种的体型进化。
2. 我们针对三种具有大陆尺度分布范围的被狩猎袋鼠属物种验证了这一假说。为此，我们测量了过去130年间采集自野生动物馆藏的2000余件袋鼠属动物头骨标本，并采用空间贝叶斯模型（spatial Bayesian models）分析数据，该模型可控制标本的年龄、性别，以及环境驱动因素与岛屿效应。
3. 我们未发现任何物种出现假说中预测的体型下降的证据；相反，拟合趋势项的模型显示，随着时间推移，这些物种的体型出现了小幅增长。这一看似违背直觉的结果，与澳大利亚欧洲殖民后捕食者类群匮乏导致的死亡率降低，以及草原植被初级生产力提升的情况相符。
4. 袋鼠属动物体型的空间分布模式支持了用于解释地理体型变异的散热极限假说和生产力假说，即头骨尺寸随夏季最高气温下降而增大，随降雨量增加而增大。
5. 目前尚无实证证据表明，体型选择性狩猎推动了澳大利亚袋鼠属动物体型小型化的进化。贝叶斯模型（Bayesian models）适合用于探究人类狩猎的长期影响，因为其可以插补缺失数据、拟合非线性生长模型，并考虑野生动物馆藏中固有的非随机空间采样偏差。