Abrupt loss of species richness caused by ecosystem transition

Ecosystem transition occurs when ecological thresholds are crossed, causing ecosystems to irreversibly shift from secure to insecure states. However, how ecosystem transition exacerbates species richness loss remains poorly understood. This hinders the effective protection of species richness, which is an urgent global priority. In this study, we integrated multiple ecosystem variables to elucidate ecosystem transition and its impacts on species richness loss. Our findings reveal that species richness declines abruptly following ecosystem transition, as insecure ecosystems are characterized by reduced plant cover and productivity, intensified warming and drying, and diminished oxygen production. Insecure ecosystems imperil the survival of all species, including 39.4% of threatened birds and 29.2% of threatened mammal species. We project that by 2100, the ecosystem areas considered insecure will encompass 40.4% of the global land areas under the RCP8.5 scenario, contributing to 51.6% of species richness loss. In contrast, hyper-secure ecosystems are projected to account for 18.1% of species richness loss. This study identifies ecosystem transition as a critical driver of species richness loss that should be accounted for by policymakers in designing targeted conservation strategies.