Distributional shifts change the biodiversity--ecosystem stability relationship under climate change

Distributional shifts under climate change are increasingly recognized as a biotic change worldwide. However, the effects of distributional shifts on ecosystem variability (i.e., temporal variability of regional ecosystem productivity) through changes in biodiversity remain to be clarified. In this study, to elucidate the impact of population-level distributional shifts under climate change on community structure and ecosystem function, we investigated three questions, using over 25 years of data on about 800 marine species: (i) the temporal changes in alpha diversity (i.e., the number of species within a local community) and beta diversity (i.e., the spatial differences in species composition among local communities), (ii) the contribution of individual species to the observed changes in biodiversity, and (iii) the changes in the relationship between biodiversity and ecosystem variability. We found that ecosystem variability was largely stabilized by beta diversity, especially in the present period (2012 to 2021), because beta diversity increased due to the invasion of species that were not present in the study area and were distributed mainly in tropic and subtropic areas. Despite the effect of beta diversity, ecosystem variability increased in the present period. This increase in ecosystem variability was associated with the spatially synchronized temporal variation in sea-bottom temperature, which resulted in synchronized temporal variation in species abundance among local communities, as well as the increased impact of alpha variability (i.e., temporal variability of alpha diversity at a local scale) on ecosystem variability. These results indicate that the impact of alpha diversity on ecosystem variability is more changeable than the impact of beta diversity on ecosystem variability under climate change, suggesting the importance of focusing on changes in alpha diversity resulting from local colonization from other habitats and local extinction in existing habitats.