Large‐Scale Variation in Biodiversity–Ecosystem Functioning (<scp>BEF</scp>) Relationships in Aquatic Metacommunities on Terrestrial Islands

ABSTRACT Aim Recent work has shown that the biodiversity of potential colonists in a landscape (the local species pool) may be more important for ecosystem functioning than the biodiversity in local habitat patches. However, it is unknown how such biodiversity–ecosystem functioning (BEF) relationships may change across different biomes. To explore such patterns, nested insular ecosystems where variation in local biodiversity and local species pool biodiversity can be reliably quantified can provide important insights. Location Rock pool metacommunities on isolated rocky outcrops (i.e., inselbergs) in Africa, Australia, Europe, and North America. Time Period Sampling: 2011–2019. Major Taxa Studied Freshwater invertebrates. Methods We assembled a large‐scale dataset of invertebrate metacommunities from replicated rock pool clusters on inselbergs as a model system to test the ability of local biodiversity and local species pool biodiversity to explain community biomass in organisms with different survival strategies (active or passive dispersers). To test our hypotheses, we used a combination of directed acrylic graph‐based path analyses and general linear mixed‐effects models. Results The biodiversity of the local species pool was influenced by climate but did not significantly impact community biomass. Instead, local environmental gradients seem to override any species pool effects on community biomass. However, in line with expectations, the relationship between local biodiversity and biomass varied across inselbergs. Contrary to expectations, inselberg prominence did not influence the BEF slope. However, in drier conditions, the BEF relationship weakened for active dispersers, likely reflecting environmental limits on recolonisation. Thus, climate and dispersal strategy jointly shaped how biodiversity influenced community biomass. Main Conclusion This study illustrates that even in a simple ecosystem there can be substantial geographical variation in the relationship between biodiversity and ecosystem functioning that may be partially explained by environmental conditions and by the survival strategy of the organisms considered.