Table_1_v1_Trait based niche differentiation in tetrakas (Bernieridae) endemic to Madagascar: A multi-isotope approach.DOCX

IntroductionTropical rainforest species interact with each other and their environment over a wide range of spatiotemporal scales. However, our understanding of resource partitioning and the mechanisms of avian species coexistence is largely restricted to subjective visual observations or acoustic monitoring. Therefore, the relative magnitudes of interspecific and intraspecific differences in resource use have remained difficult to quantify, particularly regarding different diets and habitat use. The eastern rainforest belt of Madagascar is inhabited by several species of insectivorous tetrakas belonging to an endemic bird family of Madagascar (Bernieridae). These species occupy similar habitats in the forest understory and are morphologically similar but because of likely differences (e.g., in foraging behaviors) we expect their foraging niches to be segregated allowing coexistence.
MethodsWe examined the niche differentiation of four of these species: the Grey-crowned Tetraka (Xanthomixis cinereiceps), Long-billed Tetraka (Bernieria madagascariensis), Spectacled Tetraka (Xanthomixis zosterops), and White-throated Oxylabes (Oxylabes madagascariensis) in the Maromizaha rainforest in eastern Madagascar combining morphometry with stable carbon, nitrogen, and sulfur isotope ratios (δ13C, δ15N, and δ34S) from feathers.
ResultsWe show considerable variation in isotopic niche positions, niche breadth and interspecific niche overlap. In two species, the Long-billed Tetraka and Spectacled Tetraka, we found an indication of sex-specific niche space, with males exhibiting a larger isotopic niche-area relative to females. Morphological traits of five species (including the Wedge-tailed Tetraka, Hartertula flavoviridis) coupled with stable isotope data provided explanations of patterns of niche overlap and isotopic position.
DiscussionThe observed isotopic niche differences may be explained by differences in resource acquisition strategies that might be associated with specific morphological traits and spatial distribution. This may play an important role in niche differentiation among coexisting and phylogenetically closely related species.

### 引言
热带雨林物种在广泛的时空尺度下，彼此间及其与环境间存在复杂的相互作用。然而，目前学界对资源划分与鸟类物种共存机制的认知，大多局限于主观目视观测与声学监测手段。因此，资源利用中种间与种内差异的相对强度始终难以量化，在不同食性与栖息地利用维度上尤为突出。
马达加斯加东部雨林带栖息着数种食虫四眉鹟，它们隶属于马达加斯加特有鸟类科——马岛鹟科（Bernieridae）。这些物种在林下层占据相似的栖息生境，形态特征也较为相近，但由于觅食行为等方面可能存在差异，我们推测其觅食生态位会发生分化，进而实现物种共存。

### 研究方法
本研究以马达加斯加东部马罗米扎哈（Maromizaha）热带雨林为研究样地，结合形态测量分析与羽毛组织的稳定碳、氮、硫同位素比值（δ¹³C、δ¹⁵N、δ³⁴S），对该区域4种四眉鹟的生态位分化展开了系统探究。这4个物种分别为：灰顶四眉鹟（Grey-crowned Tetraka, *Xanthomixis cinereiceps*）、长嘴四眉鹟（Long-billed Tetraka, *Bernieria madagascariensis*）、眼镜四眉鹟（Spectacled Tetraka, *Xanthomixis zosterops*）以及白喉奥鹟（White-throated Oxylabes, *Oxylabes madagascariensis*）。

### 研究结果
研究结果显示，同位素生态位位置、生态位宽度以及种间生态位重叠度均存在显著变异。在长嘴四眉鹟与眼镜四眉鹟两个物种中，我们观测到其生态位空间存在性别分化的迹象：雄性个体的同位素生态位面积显著大于雌性个体。结合包括楔尾四眉鹟（*Hartertula flavoviridis*）在内的5个物种的形态特征与稳定同位素数据，我们得以解释生态位重叠与同位素生态位位置的分布格局。

### 讨论
本研究观测到的同位素生态位差异，可通过资源获取策略的差异得到合理解释，而这类策略可能与特定的形态特征以及空间分布密切相关。这一机制在共存且系统发育关系密切的物种间的生态位分化过程中，可能发挥着关键作用。