Data from: Niche divergence promotes rapid diversification of East African sky island white-eyes (Aves: Zosteropidae)

The Eastern Afromontane biodiversity hotspot composed of highly fragmented forested highlands (sky islands) harbours exceptional diversity and endemicity, particularly within birds. To explain their elevated diversity within this region, models founded on niche conservatism have been offered, although detailed phylogeographic studies are limited to a few avian lineages. Here we focus on the recent songbird genus Zosterops, represented by montane and lowland members, to test the roles of niche conservatism versus niche divergence in the diversification and colonization of East Africa’s sky islands. The species-rich white-eyes are a typically homogeneous family with an exceptional colonizing ability, but in contrast to their diversity on oceanic islands, continental diversity is considered depauperate and has been largely neglected. Molecular phylogenetic analysis reveals extensive polyphyly among different montane populations of Z. poliogastrus with these larger and heavier endemic populations more closely related to taxa with divergent habitat types, altitudinal distributions and dispersal abilities than they are to populations of restricted endemics that occur in neighbouring montane forest fragments. This repeated transition between lowland and highland habitats over time demonstrate that diversification of the focal group is explained by niche divergence. The results also highlight an underestimation of diversity compared to morphological studies that has implications for their taxonomy and conservation. Molecular dating suggests that the spatially extensive African radiation arose exceptionally rapidly (1-2.5 Ma) during the fluctuating Plio-Pleistocene climate, which may have provided the primary driver for lineage diversification.由高度破碎的森林高地（天空岛，sky islands）构成的东非山地生物多样性热点区域，拥有极高的物种多样性与特有性水平，在鸟类类群中尤为显著。为解释该区域内该类群多样性的异常抬升，学界已提出基于生态位保守性（niche conservatism）的理论模型，但针对该区域的详细系统地理学（phylogeography）研究仅局限于少数鸟类支系。本研究聚焦于绣眼鸟属（Zosterops）——一类包含山地与低海拔分布类群的鸣禽属——以检验生态位保守性与生态位分化（niche divergence）在东非“天空岛”的物种分化与种群定居过程中的作用。物种丰富的绣眼鸟科通常表现出较高的形态同质化特征，且具备极强的跨区域定居能力；但与海洋岛屿上的丰富多样性不同，大陆分布的绣眼鸟类群多样性被认为较为匮乏，相关研究也长期被忽视。分子系统发育（molecular phylogenetic）分析显示，灰腹绣眼鸟（Zosterops poliogastrus）的不同山地种群间存在广泛的多系现象（polyphyly）；相较于栖息于邻近山地森林片段的狭布特有种群，这些体型更大、更为粗壮的特有种群，与那些生境类型、海拔分布及扩散能力均存在显著差异的类群亲缘关系更近。这类反复发生的低海拔-高海拔生境转换事件表明，本研究关注类群的物种分化可由生态位分化得以解释。研究结果同时显示，相较于形态学研究，该类群的实际多样性被低估，这一结论对其分类学研究与物种保护工作均具有重要启示。分子定年（molecular dating）结果表明，空间分布范围广泛的非洲绣眼鸟支系辐射演化事件发生异常迅速（距今100万至250万年），且对应上新世-更新世（Plio-Pleistocene）时期的气候波动阶段，该气候波动可能是驱动支系分化的核心因素。