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

Background: Inselbergs (granitic and gneissic rock outcrops) are common elements in the Atlantic Forest and present large taxonomic (TD), functional (FD) and phylogenetic (PD) diversity. Aims: 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. Methods: 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. Results: 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. Conclusions: 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：岛状孤岩（Inselbergs，即花岗岩与片麻岩质岩石露头）是大西洋森林（Atlantic Forest）中的常见景观要素，且拥有极高的分类多样性（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：本研究通过对比两座岛状孤岩内部及相互间的群落分类、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。我们预期不同孤岩间的功能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——这一预期源于岛状孤岩的局部环境条件相似，且不同孤岩的谱系长期处于隔离状态。 研究方法：本研究计算了分类、功能与系统发育多样性，并将多样性划分为α（单座岛状孤岩）、β（两座孤岩之间）与γ（整体样本）三个组分。同时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，本研究开展了冗余分析。以斑块面积与两座岛状孤岩作为预测因子，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：两座岛状孤岩在分类多样性上存在差异，但功能与系统发育多样性表现出趋同性。系统发育信号的保留程度有限，这表明不同物种可能发生趋同演化，并对环境变量产生相似的响应。在单座岛状孤岩内部，面积更大的斑块具备更高的分类、功能与系统发育多样性。 研究结论：为岛状孤岩制定保护策略颇具挑战性——尽管不同孤岩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具备独特性。