Patterns of Phylogenetic Diversity of Subtropical Rainforest of the Great Sandy Region, Australia Indicate Long Term Climatic Refugia

Australia’s Great Sandy Region is of international significance containing two World Heritage areas and patches of rainforest growing on white sand. Previous broad-scale analysis found the Great Sandy biogeographic subregion contained a significantly more phylogenetically even subset of species than expected by chance contrasting with rainforest on white sand in Peru. This study aimed to test the patterns of rainforest diversity and relatedness at a finer scale and to investigate why we may find different patterns of phylogenetic evenness compared with rainforests on white sands in other parts of the world. This study focussed on rainforest sites within the Great Sandy and surrounding areas in South East Queensland (SEQ), Australia. We undertook field collections, expanded our three-marker DNA barcode library of SEQ rainforest plants and updated the phylogeny to 95% of the SEQ rainforest flora. We sampled species composition of rainforest in fixed area plots from 100 sites. We calculated phylogenetic diversity (PD) measures as well as species richness (SR) for each rainforest community. These combined with site variables such as geology, were used to evaluate patterns and relatedness. We found that many rainforest communities in the Great Sandy area were significantly phylogenetically even at the individual site level consistent with a broader subregion analysis. Sites from adjacent areas were either not significant or were significantly phylogenetically clustered. Some results in the neighbouring areas were consistent with historic range expansions. In contrast with expectations, sites located on the oldest substrates had significantly lower phylogenetic diversity (PD). Fraser Island was once connected to mainland Australia, our results are consistent with a region geologically old enough to have continuously supported rainforest in refugia. The interface of tropical and temperate floras in part also explains the significant phylogenetic evenness and higher than expected phylogenetic diversity.

澳大利亚大沙区（Great Sandy Region）具有国际重要价值，境内坐落着两处世界遗产（World Heritage）区域，还分布着生长在白色砂地上的雨林斑块。此前的大范围分析表明，与秘鲁白色砂地上的雨林相比，大沙生物地理亚区（biogeographic subregion）的物种子集在系统发育均匀度（phylogenetic evenness）上显著高于随机预期的结果。本研究旨在以更精细的尺度检验雨林多样性与亲缘关系格局，并探究为何与全球其他地区白色砂地上的雨林相比，本区域会呈现出不同的系统发育均匀度模式。本研究聚焦于澳大利亚昆士兰州东南部（South East Queensland, SEQ）大沙区及周边区域的雨林样地。我们开展了野外采集工作，扩充了昆士兰州东南部雨林植物的三标记DNA条形码（DNA barcode）数据库，并将系统发育树更新至覆盖该区域95%的雨林植物区系。我们在100个样地的固定面积样方中采集了雨林物种组成数据，计算了每个雨林群落的系统发育多样性（phylogenetic diversity, PD）与物种丰富度（species richness, SR）指标。结合地质等生境变量，我们对群落分布格局及其亲缘关系进行了评估。研究结果显示，大沙区的多数雨林群落在样地尺度上呈现出显著的系统发育均匀度，这与此前的大范围亚区分析结果一致。相邻区域的样地要么无显著统计差异，要么呈现出显著的系统发育聚集（phylogenetic clustering）格局。邻近区域的部分结果与历史上的物种分布区扩张现象相符。与预期相悖的是，位于最古老基质上的样地，其系统发育多样性（PD）显著更低。弗雷泽岛（Fraser Island）曾与澳大利亚大陆相连，本研究结果与该区域地质年代足够久远、可长期作为雨林避难所的推论相契合。热带与温带植物区系的交汇作用，在一定程度上也解释了该区域雨林为何呈现出显著的系统发育均匀度，以及高于预期的系统发育多样性。