According to the island syndrome and island rule hypotheses, island isolation and reduced area lead to phenotypic shifts in ecologically relevant traits in insular populations compared to mainland ones. These hypotheses have been built up with oceanic islands in mind or islands where isolation is high and colonization rate relatively limited. This set of hypotheses, however, may not be applicable to other inland–island systems or recently fragmented landscapes. We investigated how island life leads to phenotypic changes in two rodent metapopulations: deer mice and red‐backed voles in a fragmented system on a river in Canada. From 2013 to 2016, we sampled 454 deer mice and 665 red‐backed voles spread across 10 islands and six mainland sites on river shores. We compared body mass, tail and hindfoot length, exploration and reaction towards predators, between individuals from island and mainland sites, and assessed the role of connectivity, isolation and area of islands. Insular individuals from both species were less aggressive towards potential predators and insular mice were more thorough explorers compared to mainland ones. Male mice were heavier and juvenile mice had longer tails on islands. However, contrary to expectations, we found negative relationships between aggressiveness and juvenile exploration score with patch connectivity for mice. Island connectivity significantly affected tail length of mice through a concave relationship. Finally, vole aggressiveness and exploration of male mice were positively correlated to island isolation. Our study supports only partially the predictions of the island syndrome hypothesis. It provides empirical evidence that inland–island life can modify traits in deer mice, but less so in red‐backed voles in a non‐oceanic system. It also raises questions about the direct causal factors of these changes in a naturally fragmented landscape, and urges for more predictive models about phenotypic/genetic divergence among populations in natural and artificial fragmented landscapes.

中文翻译：

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内陆-岛屿系统中的两种啮齿动物物种仅部分验证了岛屿综合症假说

根据岛屿综合症和岛屿规则假设，与大陆地区相比，岛屿孤立和岛屿面积减少导致岛屿人口生态相关性状的表型转移。这些假设的建立是考虑到海洋岛屿或孤立程度高且殖民化率相对有限的岛屿。但是，这组假设可能不适用于其他内陆-岛屿系统或近期零散的景观。我们调查了岛屿生活如何导致两种啮齿动物亚群的表型变化：在加拿大河流的零散系统中，鹿鼠和赤背田鼠。从2013年到2016年，我们采样了454只鹿鼠和665只红背田鼠，它们分布在10个岛屿和六个内陆河岸地区。我们比较了体重，尾巴和后足的长度，对掠食者的探索和反应，岛屿和大陆站点的个人之间的联系，并评估了连接，隔离和岛屿面积的作用。与大陆动物相比，来自这两个物种的岛上个体对潜在的捕食者的攻击性都较小，而岛上小鼠则是更全面的探索者。雄性小鼠较重，幼年小鼠的岛上尾巴较长。但是，与预期相反，我们发现攻击性和少年探索得分与小鼠斑片连接性之间存在负相关关系。岛连接通过凹关系显着影响小鼠的尾巴长度。最后，田鼠的侵略性和雄性小鼠的探索与孤岛呈正相关。我们的研究仅部分支持岛屿综合症假说的预测。它提供了经验证据，表明内陆-岛上的生命可以改变鹿类小鼠的性状，但在非海洋系统中，红背田鼠的性状却很少。它还提出了关于自然零散景观中这些变化的直接因果的问题，并敦促建立更多关于自然和人工零散景观中种群表型/遗传差异的预测模型。