High plant taxonomic beta diversity and functional and phylogenetic convergence between two Neotropical inselbergs

<b>Background</b>: Inselbergs (granitic and gneissic rock outcrops) are common elements in the Atlantic Forest and present large taxonomic (TD), functional (FD) and phylogenetic (PD) diversity. <b>Aims</b>: We investigated how plant diversity changed across ecological and biogeographic scales by comparing TD, FD and PD of communities within and between two inselbergs. We expected converging FD and PD but distinct TD between outcrops, because of similar local environmental conditions in inselbergs and the long-term lineage isolation. <b>Methods</b>: We calculated TD, PD and FD, and partitioned diversity into α (each inselberg), β (between inselbergs) and γ (whole sample) components. Phylogenetic signal was estimated for all traits. To link environmental predictors to functional traits a redundancy analysis was run. Variation in TD, FD and PD was analysed by general linear models with patch area and the two inselbergs as predictors. <b>Results</b>: The inselbergs were taxonomically different, but showed convergence in their functional and phylogenetic diversity. The limited retention of phylogenetic signal suggests that different species may converge and respond similarly to environmental variables. Within inselbergs, larger patches displayed higher TD, FD and PD. <b>Conclusions</b>: Seeking conservation strategies for inselbergs is challenging since, despite their functional and phylogenetic similarity, endemic species make individual rock outcrops unique.

研究背景：岛状山（Inselbergs，花岗岩与片麻岩质岩石露头）是大西洋森林中的典型地貌单元，具备极高的分类多样性（Taxonomic Diversity, TD）、功能多样性（Functional Diversity, FD）与系统发育多样性（Phylogenetic Diversity, PD）。研究目的：本研究通过比较两座岛状山内部及相互之间植物群落的分类、功能与系统发育多样性，探究植物多样性在生态与生物地理尺度上的变化规律。鉴于岛状山具有相似的局域环境条件且谱系长期隔离，我们预测不同岩石露头间的功能多样性与系统发育多样性将趋于一致，而分类多样性则存在显著差异。研究方法：本研究计算了群落的分类、功能与系统发育多样性，并将其划分为α（单座岛状山）、β（两座岛状山之间）以及γ（总样本）三个多样性组分；对所有功能性状估算了系统发育信号；为关联环境预测因子与功能性状，开展了冗余分析；以斑块面积和两座岛状山作为预测变量，通过广义线性模型分析了分类、功能与系统发育多样性的变异情况。研究结果：两座岛状山的分类多样性存在显著差异，但功能多样性与系统发育多样性却表现出趋同性；系统发育信号的保留程度有限，提示不同物种可能发生趋同演化并对环境变量产生相似响应；在单座岛状山内部，斑块面积越大，其分类、功能与系统发育多样性越高。研究结论：尽管岛状山之间的功能与系统发育多样性相似，但特有物种使得每一处岩石露头都独具特色，因此制定岛状山的保护策略颇具挑战。