Small mammal assemblages from South America provide a unique opportunity to measure coexistence and niche partitioning between marsupials and placentals. We tested how these two major clades partition environmental resources by comparing stable isotopic ratios of similar sized Didelphidae and Sigmodontinae in four Brazilian biomes: Pampas grassland, Pantanal wetland, Cerrado woodland savanna, and Atlantic Forest. Generally, didelphid isotopic niche follows a scaling law, because we found an association between δ15N enrichment and body mass. Sigmodontines that primarily partition the environment via forest strata showed a greater intake of C4 or/and crassulacean acid metabolism (CAM) plants than didelphids, as reflected by their wider trophic niche. Values of δ13C were highest in savannas and grasslands (Cerrado and Pampas biomes), and values of δ15N were highest in the Atlantic Forest (in sigmodontines) and Pampas (in didelphids). While assessing patterns between the two major Brazilian biomes (Atlantic Forest and Cerrado), we found evidence of a broader trophic niche for both clades in the Cerrado. In the Atlantic Forest, niche occupation by Didelphidae was completely enclosed within the Sigmodontinae trophic niche. Both clades showed less overlap in the Cerrado, a less productive environment. Our results highlight the importance of a comparative framework and the use of stable isotopes for testing ecological questions related to how small mammalian communities partition their niche.

中文翻译：

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小型哺乳动物的生态位划分：使用稳定同位素的种间和生物群落分析

来自南美洲的小型哺乳动物组合提供了一个独特的机会来衡量有袋动物和胎盘之间的共存和生态位划分。我们通过比较四个巴西生物群落中相似大小的双鳐科和 Sigmodontinae 的稳定同位素比率来测试这两个主要进化枝如何分配环境资源：潘帕斯草原、潘塔纳尔湿地、塞拉多林地稀树草原和大西洋森林。一般来说，didelphid 同位素生态位遵循比例定律，因为我们发现 δ15N 富集与体重之间存在关联。主要通过森林地层划分环境的 Sigmodontines 表现出比 didelphids 更多的 C4 或/和景天酸代谢 (CAM) 植物的摄入量，这反映在它们更广泛的营养生态位上。δ13​​C 值在稀树草原和草原（塞拉多和潘帕斯生物群落）中最高，δ15N 值在大西洋森林（sigmodontines）和潘帕斯（didelphids）中最高。在评估巴西两个主要生物群落（大西洋森林和塞拉多）之间的模式时，我们发现了塞拉多两个进化枝更广泛的营养生态位的证据。在大西洋森林，Didelphidae 的生态位占据完全封闭在 Sigmodontinae 营养生态位内。两个进化枝在塞拉多的重叠较少，这是一个生产力较低的环境。我们的结果强调了比较框架的重要性以及使用稳定同位素来测试与小型哺乳动物群落如何划分其生态位相关的生态问题。我们发现了塞拉多两个进化枝更广泛的营养生态位的证据。在大西洋森林，Didelphidae 的生态位占据完全封闭在 Sigmodontinae 营养生态位内。两个进化枝在塞拉多的重叠较少，这是一个生产力较低的环境。我们的结果强调了比较框架的重要性以及使用稳定同位素来测试与小型哺乳动物群落如何划分其生态位相关的生态问题。我们发现了塞拉多两个进化枝更广泛的营养生态位的证据。在大西洋森林，Didelphidae 的生态位占据完全封闭在 Sigmodontinae 营养生态位内。两个进化枝在塞拉多的重叠较少，这是一个生产力较低的环境。我们的结果强调了比较框架的重要性以及使用稳定同位素来测试与小型哺乳动物群落如何划分其生态位相关的生态问题。