Data from: Environmental niche conservatism explains the accumulation of species richness in Mediterranean-hotspot plant genera

The causes of exceptionally high plant diversity in Mediterranean-climate biodiversity hotspots are not fully understood. We asked whether a mechanism similar to the tropical niche conservatism hypothesis could explain the diversity of four large genera (Protea, Moraea, Banksia, and Hakea) with distributions within and adjacent to the Greater Cape Floristic Region (South Africa) or the Southwest Floristic Region (Australia). Using phylogenetic and spatial data we estimated the environmental niche of each species, and reconstructed the mode and dynamics of niche evolution, and the geographic history, of each genus. For three genera there were strong positive relationships between the diversity of clades within a region and their inferred length of occupation of that region. Within genera, there was evidence for strong evolutionary constraint on niche axes associated with climatic seasonality and aridity, with different niche optima for hotspot and non-hotspot clades. Evolutionary transitions away from hotspots were associated with increases in niche breadth and elevated rates of niche evolution. Our results point to a process of “hotspot niche conservatism” whereby the accumulation of plant diversity in Mediterranean-type ecosystems results from longer time for speciation, with dispersal away from hotspots limited by narrow and phylogenetically-conserved environmental niches.

地中海气候生物多样性热点地区内植物多样性异常高的成因尚未完全明晰。本研究旨在检验类似热带生态位保守假说（tropical niche conservatism hypothesis）的机制，能否解释分布于大开普植物区（Greater Cape Floristic Region，南非）及其邻近区域、或西南植物区（Southwest Floristic Region，澳大利亚）内的4个大属——帝王花属（Protea）、肖鸢尾属（Moraea）、班克木属（Banksia）与哈克木属（Hakea）的物种多样性格局。我们借助系统发育数据与空间数据，估算了每个物种的环境生态位，并重建了各属的生态位演化模式与动态，以及属的地理演化历史。分析结果显示，在3个属中，某一区域内的支系多样性与其被推断占据该区域的时长存在显著正相关关系。在属内水平，存在显著的进化约束作用于与气候季节性、干旱度相关的生态位轴，且热点支系与非热点支系具有不同的生态位最适值。从热点区域向外的进化转移，往往伴随着生态位宽度的增加与生态位演化速率的提升。本研究结果指向“热点生态位保守”过程：地中海型生态系统中植物多样性的积累，源于更长的物种形成时间，而从热点区域向外的扩散则受限于狭窄且系统发育保守的环境生态位。