In seasonal environments, the winter months can drive the structure and dynamics of vertebrate communities. Most ecological studies have focused on species above the snow, overlooking those within the subnivium (below-snow environment). The Great Lakes region of North America is characterized by seasonal snow cover and a diverse assemblage of small mammals, both of which are changing rapidly in response to a changing climate. To study the seasonal dynamics of small mammals, we sampled communities in three forest types (hardwood, hemlock-cedar, and spruce bog) in summer and winter over 2 years. We hypothesized that seasonal differences in communities would be moderated by forest structure in summer and snow in winter. We assessed community dominance via species diversity and the abundances of deer mice (Peromyscus maniculatus), white-footed mice (P. leucopus), and southern red-backed voles (Myodes gapperi). We estimated a Community Temperature Index (CTI; a metric of the balance between warm- and cold-adapted species in a community) and tested seasonal drivers of CTI. Species diversity was highest in spruce bogs in winter due to increased species evenness, but diversity was consistent year-round in hardwood and hemlock-cedar forests due to unchanging species dominance. Spruce bogs supported the coldest CTI in summer, but CTIs converged across forest types in winter. In summer, forest structure drove CTI; in winter, colder CTIs were associated with deeper snow and a warmer subnivium. Our work reveals that snow is a critical habitat and filter for cold-adapted species that ultimately structures small mammal communities. Given rapid changes in snow conditions due to climate change, we predict continued range contractions for subnivium-adapted species.

中文翻译：

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雪域森林中的小型哺乳动物动态

在季节性环境中，冬季可以推动脊椎动物群落的结构和动态。大多数生态学研究都集中在雪地上的物种，而忽略了 subnivium 内的物种（雪下环境）。北美五大湖地区的特点是季节性积雪和多样化的小型哺乳动物群落，这两者都随着气候变化而迅速变化。为了研究小型哺乳动物的季节性动态，我们在 2 年的夏季和冬季对三种森林类型（硬木、铁杉雪松和云杉沼泽）的群落进行了抽样调查。我们假设社区的季节性差异将受到夏季森林结构和冬季降雪的缓和。我们通过物种多样性和鹿鼠（Peromyscus maniculatus）、白足鼠（P. leucopus) 和南部红背田鼠 (Myodes gapperi)。我们估计了一个社区温度指数（CTI；衡量社区中适应温冷的物种之间平衡的指标）并测试了 CTI 的季节性驱动因素。由于物种均匀度增加，冬季云杉沼泽的物种多样性最高，但由于物种优势不变，硬木和铁杉雪松林的多样性全年保持一致。云杉沼泽支持夏季最冷的 CTI，但 CTI 在冬季跨森林类型汇聚。夏季，森林结构带动 CTI；在冬季，较冷的 CTI 与较深的积雪和较暖的 subnivium 有关。我们的工作表明，雪是适应寒冷的物种的重要栖息地和过滤器，最终构成小型哺乳动物群落。鉴于气候变化导致雪况迅速变化，