Data from: Evolution of a hotspot genus: geographic variation in speciation and extinction rates in Banksia (Proteaceae)

Background: Hotspots of angiosperm species richness and endemism in Mediterranean-climate regions are among the most striking, but least well-understood, geographic patterns of biodiversity. Recent studies have emphasized the importance of rapid diversification within hotspots, compared to non-hotspot regions, as a major contributor to these patterns. We constructed the first near-complete phylogeny of Banksia (Proteaceae) to test whether diversification rates have differed between lineages confined to the southwest Australian hotspot and those found throughout southern, eastern and northern Australia. We then tested for variation in diversification rates among the bioclimatic zones within the southwest hotspot itself. Results: Although Banksia species richness in the southwest is ten times that of the rest of the continent, we find little evidence for more rapid diversification in the southwest, although this result is inconclusive. However, we find firmer support for substantial rate variation within the southwest hotspot, with more rapid diversification in the semi-arid heaths and shrublands, compared to the high-rainfall forests. Most of the Banksia diversity of the southwest appears to be generated in the heaths and shrublands, with a high migration rate out of this zone boosting diversity of the adjacent forest zone. Conclusions: The geographic pattern of diversification in Banksia appears more complex than can be characterized by a simple hotspot vs. non-hotspot comparison, but in general, these findings contrast with the view that the high diversity of Mediterranean hotspots is underpinned by rapid radiations. Steady accumulation of species at unexceptional rates, but over long periods of time, may also have contributed substantially to the great botanical richness of these regions.

研究背景：地中海气候区域的被子植物物种丰富度与特有性热点区域，是生物多样性领域最引人瞩目却又最缺乏系统阐释的地理分布格局之一。近期研究强调，相较于非热点区域，热点区域内的快速物种分化是塑造这类格局的核心驱动因素。本研究构建了首个近乎完整的山龙眼科（Proteaceae）班克木属（Banksia）系统发育树，以检验局限于澳大利亚西南部热点区域的支系，与分布于澳大利亚南部、东部及北部的支系之间的物种分化速率是否存在差异。随后，我们进一步检验了澳大利亚西南部热点区域内部不同生物气候带间的物种分化速率变异情况。
研究结果：尽管澳大利亚西南部的班克木物种丰富度达到澳洲大陆其余区域的十倍，但我们并未发现该区域物种分化速率更快的有力证据，这一结果尚无定论。不过，我们在西南部热点区域内部发现了更为确凿的物种分化速率差异证据：相较于高降雨森林地带，半干旱灌丛与矮灌群落的物种分化速率更快。澳大利亚西南部绝大多数的班克木多样性似乎起源于灌丛与矮灌群落，而该区域向外的高迁移率进一步提升了邻近森林区域的物种多样性。
研究结论：班克木属的物种分化地理格局远比简单的"热点与非热点"对比所能刻画的更为复杂。总体而言，本研究结果与"地中海气候生物多样性热点区域的高物种丰富度依托于快速辐射演化"这一传统观点相悖。以恒定速率长期持续积累物种，也可能对这类区域极高的植物物种丰富度做出了重要贡献。