Geodiversity accounts for fish diversity in the Lancang-Mekong River

AbstractAim: Geodiversity offers novel insights into biodiversity patterns and their underlying mechanisms, thereby contributing to the development of conservation strategies amid widespread environmental changes and human disturbances. However, the relationship between geodiversity and biodiversity remains largely unexplored, particularly in freshwater ecosystems. This study investigates the extent to which geodiversity accounts for fish diversity across dimensions (taxonomic, functional, and phylogenetic) and levels (alpha and beta) of biodiversity in a large river.Location: Lancang-Mekong River.Time period: 1935-2023.Taxa studied: Freshwater fishes.Methods: We first compiled three freshwater fish datasets (i.e., occurrence records, functional traits, and phylogenetic relations) and eight geofeature group datasets (i.e., water temperature, discharge, waterbody topography, terrestrial cover, landform, soil, and rock) of the catchment. Then, we calculated multidimensional fish diversity and geodiversity at alpha and beta levels, respectively. Next, we assessed the influence of geodiversity on multidimensional fish diversity at corresponding levels using Bayesian generalized linear mixed models (GLMMs) and structural equation models (SEMs).Results: Multidimensional fish diversity showed congruent patterns across diversity levels, with alpha diversity showing positive upriver-downriver gradients but beta diversity showing negative gradients along the river continuum. The spatial congruence in geodiversity was weak across geofeatures and diversity levels. Geodiversity substantially accounted for the variance in fish diversity and had consistent effect directions across dimensions of biodiversity at corresponding levels, with conditional R2 in Bayesian GLMMs ranging from 0.90 to 0.98. The geodiversity associated with hydrological component accounted for multidimensional fish diversity at two levels. The SEMs revealed that the indirect effects of geodiversity on multidimensional fish diversity were widespread but generally weak.Main conclusions: Our findings emphasize the profound impact of geodiversity relating to environmental heterogeneity and resource availability on multidimensional fish diversity in large rivers. We advocate to incorporate both geodiversity and biodiversity into conservation to guide freshwater ecosystem management.研究目标：地质多样性（geodiversity）为生物多样性格局及其内在调控机制提供了全新认知，有助于在全球普遍存在的环境变化与人类干扰背景下制定生物多样性保护策略。然而，地质多样性与生物多样性之间的关联仍未得到充分探索，在淡水生态系统中这一问题尤为突出。本研究针对大型河流，探究地质多样性能够在多大程度上解释生物多样性的不同维度（分类学、功能学与系统发育学维度）以及不同层级（α多样性与β多样性）下的鱼类多样性。 研究区域：澜沧江-湄公河流域（Lancang-Mekong River） 时间跨度：1935年—2023年 研究类群：淡水鱼类 研究方法：本研究首先整理了该流域的三类淡水鱼类数据集，即物种出现记录、功能性状数据与系统发育关系数据，以及八类地貌特征组数据集，涵盖水温、径流量、水体地形、陆地覆被、地形地貌、土壤与岩石。随后，我们分别计算了不同层级下的多维度鱼类多样性与地质多样性。接下来，我们采用贝叶斯广义线性混合模型（Bayesian generalized linear mixed models, GLMMs）与结构方程模型（structural equation models, SEMs），评估了地质多样性对对应层级下多维度鱼类多样性的影响。 研究结果：多维度鱼类多样性在不同多样性层级上呈现出一致的空间格局：α多样性沿河流呈现从上游到下游逐渐升高的梯度，而β多样性则沿河流连续体呈现下降梯度。不同地貌特征与多样性层级之间的地质多样性空间一致性较弱。地质多样性能够显著解释鱼类多样性的变异，且在对应层级的生物多样性各维度上表现出一致的效应方向，贝叶斯GLMMs的条件决定系数（conditional R²）介于0.90至0.98之间。与水文组分相关的地质多样性能够解释两个层级下的多维度鱼类多样性。结构方程模型结果显示，地质多样性对多维度鱼类多样性的间接效应普遍存在，但整体强度较弱。 主要结论：本研究结果强调，与环境异质性及资源可获得性相关的地质多样性，对大型河流中的多维度鱼类多样性具有深远影响。我们倡议将地质多样性与生物多样性一同纳入保护框架，以指导淡水生态系统的管理实践。