Data from: Ecological limits on diversification of the Himalayan core Corvoidea

Within regions, differences in the number of species among clades must be explained by clade age, net diversification rate, or immigration. We examine these alternatives by assessing historical causes of the low diversity of a bird parvorder in the Himalayas (the core Corvoidea, 57 species present) relative to its more species rich sister clade. The core Corvoidea contain ecologically diverse species spanning a large range of body sizes and elevations. Despite this diversity, on the basis of ecological, morphological, and phylogenetic information, we infer that the best explanation for the low number of species within the core Corvoidea is one in which ecology limits diversification. Within the core Corvoidea, body size is correlated with elevation; large species are found at high elevations, and small species at lower elevations. Cladogenetic events leading to ecological differences between species in body size and shape mostly occurred millions of years ago, and the rate of evolutionary change has declined towards the present. Elevational distributions have been evolutionarily more labile, but are also associated with ancient cladogenetic events. We suggest the core Corvoidea occupy a restricted volume of ecological space in competition with other bird species, and this limits in situ diversification and/or immigration.

在同一区域内，不同演化支（clade）的物种数量差异，可由演化支的形成时长、净多样化速率或物种迁入事件予以解释。我们通过评估喜马拉雅地区某一鸟类小目——核心鸦类群（core Corvoidea，现存57种）——相较于其物种更丰富的姊妹演化支（sister clade）多样性偏低的历史成因，来检验上述三种可能性。核心鸦类群包含生态位多样的物种，其体型与海拔分布跨度均较大。尽管该类群具备如此多样性，但基于生态学、形态学与系统发育学信息，我们推断核心鸦类群物种数量偏低的最优解释为：生态位限制了其多样化进程。在核心鸦类群内部，体型与海拔呈显著相关：大体型物种分布于高海拔区域，小体型物种则栖息于低海拔区域。导致物种间体型与形态生态差异的成支事件（cladogenetic event）大多发生于数百万年前，且演化变化速率随时间推移逐渐降低。海拔分布的演化可塑性相对更强，但同样与古老的成支事件相关联。我们认为，核心鸦类群在与其他鸟类类群的竞争中仅占据了有限的生态空间，这一情况限制了其就地多样化（in situ diversification）与/或物种迁入过程。