Data from: Feed or fight: testing the impact of food availability and intraspecific aggression on the functional ecology of an island lizard

Body size often varies among insular populations relative to continental conspecifics – the ‘island rule’ – and functional, context-dependent morphological differences tend to track this body size variation on islands. Two hypotheses are often proposed as potential drivers of insular population differences in morphology: one relating to diet and the other involving intraspecific competition and aggression. We directly tested whether differences in morphology and maximum bite capacity were explained by interisland changes in hardness of both available and consumed prey, and levels of lizard-to-lizard aggression among small-island populations. Our study included 11 islands in the Greek Cyclades and made use of a gradient in island area spanning five orders of magnitude. We focused on the widespread lizard Podarcis erhardii. We found that on smaller islands, P. erhardii body size was larger, head height was larger relative to body size, and maximum bite capacity became proportionally stronger. This pattern in morphology and performance was not related to differences in diet, but was highly correlated with proxies of intraspecific aggression – bite scars and missing toes. Our findings suggest that critical functional traits such as body size and bite force in P. erhardii follow the predictions of the island rule and are changing in response to changes in the competitive landscape across islands of different sizes.岛屿种群的体型往往与大陆同物种种群存在差异——这便是“岛屿法则（island rule）”；而岛屿上功能依赖于环境的形态差异，往往伴随这种体型变化而出现。针对岛屿种群的形态差异，学界常提出两类潜在驱动假说：其一与食物资源相关，其二则涉及种内竞争与攻击行为。本研究直接验证了：形态与最大咬合力的差异，是否可由岛屿间可获得猎物及实际捕食猎物的硬度变化，以及小岛种群内的蜥蜴种内攻击水平来解释。本研究选取了希腊基克拉泽斯群岛的11座岛屿，利用了跨度达五个数量级的岛屿面积梯度开展实验，研究对象为广布蜥蜴Podarcis erhardii。研究发现，在面积更小的岛屿上，Podarcis erhardii的体型更大，头部高度相对于体型的比例更高，且最大咬合力也相应更强。这种形态与性能的变化模式与食物资源差异无关，但与种内攻击行为的替代指标——咬痕与断趾——高度相关。本研究结果表明，Podarcis erhardii的体型与咬合力等关键功能性状，符合岛屿法则的预测，并会随着不同面积岛屿间的竞争环境变化而发生改变。