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.