The study examines the extent to which biodiversity changes in local assemblages contribute to global biodiversity loss. By analyzing 100 time-series data from various biomes worldwide, the authors find that while community composition changes systematically over time, α diversity (diversity within a sample) does not show systematic loss. This suggests that local and regional assemblages are experiencing a substitution of taxa rather than systematic biodiversity loss. The findings highlight the need to focus on changes in species composition, which have been widespread over the past 40 years, to inform conservation and management decisions.The study examines the extent to which biodiversity changes in local assemblages contribute to global biodiversity loss. By analyzing 100 time-series data from various biomes worldwide, the authors find that while community composition changes systematically over time, α diversity (diversity within a sample) does not show systematic loss. This suggests that local and regional assemblages are experiencing a substitution of taxa rather than systematic biodiversity loss. The findings highlight the need to focus on changes in species composition, which have been widespread over the past 40 years, to inform conservation and management decisions.