True Locals: Taxonomic, Phylogenetic and Functional Diversity Level Off at Short Distances in Groundwater Amphipods in the Western Balkans

ABSTRACT Aim Multi‐faceted and multi‐scale biodiversity assessments and disentangling the factors driving the biodiversity patterns are fundamental for effective protection of biodiversity and prediction of future community changes. Despite its importance, groundwater is still a data‐deficient and under‐studied ecosystem. Here, to fill the knowledge gap, we quantify multiple facets of beta diversity (βD) and identify their drivers on a regional level in a groundwater biodiversity hotspot. Location Western Balkans, Europe. Taxon Subterranean amphipods of the family Niphargidae. Methods We compiled three datasets: distribution, phylogeny, and functional traits of Niphargidae and assessed taxonomic (TβD), phylogenetic (PβD) and functional beta diversity (FβD) at different spatial scales. We evaluated the spatial variability between these different facets and identified the drivers of βD patterns using generalised dissimilarity models (GDMs). Lastly, we constructed null models to test whether geographic distance nonrandomly explains βD in observed groundwater communities. Results We found a high βD with a dominant replacement component in all three facets, but their spatial patterns were incongruent. GDMs revealed that geographic distance between communities was by far the most significant predictor of βD in all three facets. Additionally, karst share and maximum temperature were important predictors of TβD and PβD. Both the results of GDMs and null models showed that the decay in community similarity mostly happens at relatively local scales (< 100 km distance) in all three facets. Main Conclusions Our results show that βD patterns in groundwater are primarily influenced by geographic distance between communities and are possibly an outcome of dispersal constraints, while the role of ecological factors remains elusive. As there is a high replacement at even relatively local scales (up to 100 km), a strategy for effective groundwater biodiversity protection in the region would require multiple smaller protected areas rather than a few large ones.