Abstract Three prominent explanations have been proposed to explain the dramatic differences in species richness across regions and elevations, (i) time for speciation, (ii) diversification rates, and (iii) ecological limits. But the relative importance of these explanations and, especially, their interplay and possible synthesis remain largely elusive. Integrating diversification analyses, null models, and geographic information systems, I study avian richness across regions and elevations of the New World. My results reveal that even though the three explanations are differentially important (with ecological limits playing the dominant role), each contributes uniquely to the formation of richness gradients. Further, my results reveal the likely interplay between the explanations. They indicate that ecological limits hinder the diversification process, such that the accumulation of species within a region gradually slows down over time. Yet, it does not seem to converge toward a hard ceiling on regional richness. Instead, species-rich regions show suppressed, but continued, diversification, coupled with signatures of possible competition (esp. Neotropical lowlands). Conversely, species-poor, newly-colonized regions show fast diversification and weak to no signs of competition (esp. Nearctic highlands). These results held across five families of birds, across grid cells, biomes, and elevations. Together, my findings begin to illuminate the rich, yet highly consistent, interplay of the mechanisms that together shape richness gradients in the New World, including the most species-rich biodiversity hotspots on the planet, the Andes and the Amazon. [Biogeography; community; competition; macroevolution; phylogenetics; richness gradient.]

中文翻译：

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新世界鸟类多样性的动态

摘要 已经提出了三个突出的解释来解释不同地区和海拔的物种丰富度的巨大差异，(i) 物种形成的时间，(ii) 多样化率，以及 (iii) 生态限制。但是这些解释的相对重要性，尤其是它们的相互作用和可能的综合，在很大程度上仍然难以捉摸。整合多样化分析、零模型和地理信息系统，我研究了新世界不同地区和海拔的鸟类丰富度。我的结果表明，尽管这三种解释的重要性不同（生态限制起主导作用），但每种解释对丰富度梯度的形成都有独特的贡献。此外，我的结果揭示了解释之间可能的相互作用。他们表明生态限制阻碍了多样化进程，使得一个地区内物种的积累随着时间的推移逐渐减慢。然而，它似乎并没有收敛到区域丰富度的硬顶。相反，物种丰富的地区表现出抑制但持续的多样化，加上可能存在竞争的迹象（特别是新热带低地）。相反，物种贫乏的新殖民地区表现出快速的多样化和弱到没有竞争迹象（尤其是近北高地）。这些结果适用于五个鸟类家族、网格单元、生物群落和海拔。总之，我的发现开始阐明形成新世界丰富度梯度的机制的丰富但高度一致的相互作用，包括地球上物种最丰富的生物多样性热点，安第斯山脉和亚马逊。[生物地理学；社区; 竞赛; 宏观进化；系统发育学；丰富度梯度。]