Tree dissimilarity determines multi‐dimensional beta‐diversity of herbivores and carnivores via bottom‐up effects

Global biodiversity decline and its cascading effects through trophic interactions pose a severe threat to human society. Establishing the impacts of biodiversity decline requires a more thorough understanding of multi-trophic interactions and, more specifically, the effects that loss of diversity in primary producers has on multi-trophic community assembly. Within a synthetic conceptual framework for multi-trophic beta-diversity, we tested a series of hypotheses on neutral and niche-based bottom-up processes in assembling herbivore and carnivore communities in a subtropical forest using linear models, hieratical variance partitioning based on linear mixed-effects models (LMMs) and simulation. We found that the observed taxonomic, phylogenetic and functional beta-diversity of both herbivorous caterpillars and carnivorous spiders were significantly and positively related to tree dissimilarity. Linear models and variance partitioning for LMMs jointly suggested that as a result of bottom-up effects, producer dissimilarities were predominant in structuring consumer dissimilarity, the strength of which highly depended on the trophic dependencies on producers, the diversity facet examined, and data quality. Importantly, linear models for standardized beta-diversities against producer dissimilarities implied a transition between niche-based processes such as environmental filtering and competitive exclusion, which supports the role of bottom-up effect in determining consumer community assembly. These findings enrich our mechanistic understanding of the 'Diversity Begets Diversity' hypothesis and the complexity of higher-trophic community assembly, which is fundamental for sustainable biodiversity conservation and ecosystem management.全球范围内生物多样性下降正对全球生态系统功能构成威胁。而特定类群的生物多样性下降又会通过营养级关系(例如，bottom-up effect上行效应和top-down effect下行效应)对不同营养级类群的生物多样性和整个生态系统产生复杂影响。在此背景下，揭示不同营养级之间生物多样性变化的关联机制对于理解多营养级组成的群落构建和生物多样性的维持机制至关重要。在多营养级群落构建机制的研究中，最为经典的“Diversity begets diversity”理论常常用于解释不同营养级alpha多样性的关联机制研究，而对于营养级之间多维度beta多样性的关联机制研究相对较少。 本研究依托中国亚热带生物多样性与生态系统功能 (BEF-China，江西德兴) 野外实验样地，对植物、植食性无脊椎动物(鳞翅目幼虫)和捕食性无脊椎动物(蜘蛛)的物种组成、功能特征数据进行了系统调查，并构建不同类群物种的种间系统发育关系。根据生态位理论和中性理论的预测，本研究分别在beta多样性观测值空间格局、beta多样性观测值变异解释和beta多样性标准值空间格局三个维度提出假设，系统评估了亚热带森林中植物组成(代表生态位过程中的上行效应)和空间距离(代表中性扩散过程)对这两个营养级群落构建的相对重要性。 研究表明，植食性和捕食性无脊椎动物的物种、谱系和功能beta多样性均与植物beta多样性存在显著正相关关系。基于线性混合模型的方差分解结果表明，植物组成的变化通过上行效应决定了植食性和捕食性无脊椎动物的群落组成结构，并且该影响同时受到营养级关系强度、多样性维度和数据质量(0-1数据/基于多度的数据)的影响。此外，基于零模型分析的beta多样性标准值空间格局也证实了生态位过程在植食性和捕食性无脊椎动物群落构建过程中的重要性。 综上所述，这些研究结果证实了植物beta多样性通过上行效应对其高营养级类群beta多样性的影响机制，进一步拓展了我们对亚热带森林中多营养级群落构建及生物多样性维持机制的理解。.