Environment filtering and dispersal limitation jointly shaped the taxonomic and phylogenetic beta diversity of natural forests in southern China

Aim

The mechanisms underlying the maintenance of biodiversity remain to be elucidated. Taxonomic diversity alone remains an unresolved issue, especially in terms of the mechanisms of species co-existence. We hypothesized that phylogenetic information could help to elucidate the mechanism of community assembly and the services and functions of ecosystems. The aim of this study was to explore the mechanisms driving floral diversity in subtropical forests and evaluate the relative effects of these mechanisms on diversity variation, by combining taxonomic and phylogenetic information.

Location

We examined 35 1-ha tree stem-mapped plots across eight National Nature Reserves in Guangxi Zhuang Autonomous Region, China.

Taxon

Trees.

Methods

We quantified the taxonomic and phylogenetic β-diversity between each pair of plots using the (abundance-based) Rao’s quadratic entropy and the (incidence-based) Sørensen dissimilarity indices. Using a null model approach, we compared the observed β-diversity with the expected diversity at random and calculated the standard effect size of the observed β-diversity deviation. Furthermore, we used distance-based redundancy analysis (dbRDA) to partition the variations in taxonomic and phylogenetic observed β-diversity and β-deviation into four parts to assess the environmental and spatial effects.

Results

The taxonomic β-deviation was related to and higher than the phylogenetic β-deviation (r = 0.74). This observation showed that the species turnover between pairwise plots was mainly the turnover of closely related species. Higher taxonomic and phylogenetic β-deviation were mainly concentrated in the pairwise karst and non-karst forest plots, indicating that the species in karst forests and in other forests were predominantly from distantly related clades. A large proportion of the variation in β-deviation was explained by the joint effect of environmental and spatial variables, while the relative importance of environmental variables was greater than that of spatial variables, probably owing to the influence of glacial refuge, and the migration and dispersal of plant species under the postglacial rapid climate change.

Main conclusions

Our study emphasized the importance of phylogeny in biodiversity research. The incorporation of taxonomic and phylogenetic information provides a perspective to explore potential underlying mechanisms that have shaped species assemblages and phylogenetic patterns in biodiversity hotspots.

研究目标
生物多样性维持的潜在机制仍有待阐明。仅基于分类学维度的多样性研究仍存在诸多未解决的难题，尤其是物种共存机制领域。本研究假设，系统发育信息（phylogenetic information）可助力阐明群落构建以及生态系统服务与功能的潜在机制。本研究旨在结合分类学与系统发育信息，探究亚热带森林植物多样性的驱动机制，并评估此类机制对多样性变异的相对影响。

研究区域
本研究在中国广西壮族自治区的8处国家级自然保护区内，对35块面积为1公顷的树木定位样地（stem-mapped plots）进行了调查。

研究类群
树木（Trees）。

研究方法
本研究分别采用基于多度的Rao二次熵（Rao’s quadratic entropy）与基于发生频率的索伦森相异指数（Sørensen dissimilarity index），对任意成对样地间的分类学β多样性（β-diversity）与系统发育β多样性进行量化。本研究采用零模型（null model）方法，将观测得到的β多样性与随机模拟的预期β多样性进行对比，并计算得到观测β多样性偏差的标准效应量（standard effect size）。此外，本研究采用基于距离的冗余分析（distance-based redundancy analysis, dbRDA），将观测得到的分类学β多样性、系统发育β多样性以及β多样性偏差的变异划分为四个组分，以评估环境因子与空间因子的影响效应。

研究结果
分类学β多样性偏差与系统发育β多样性偏差呈显著正相关（r=0.74），且前者显著高于后者。该结果表明，成对样地间的物种更替主要为近缘物种间的更替。较高的分类学与系统发育β多样性偏差主要集中在喀斯特森林与非喀斯特森林的成对样地中，这表明喀斯特森林与其他森林中的物种主要源自亲缘关系较远的演化支（clade）。β多样性偏差的大部分变异可由环境变量与空间变量的联合效应解释，且环境变量的相对重要性高于空间变量，该现象可能与冰期避难所（glacial refuge）的影响，以及冰期后快速气候变化背景下植物物种的迁移与扩散有关。

主要结论
本研究强调了系统发育信息在生物多样性研究中的核心价值。结合分类学与系统发育信息，可为探究塑造生物多样性热点地区（biodiversity hotspot）物种组合与系统发育格局的潜在机制提供全新研究视角。