PHYSIOLOGICALLY DRIVEN HOMOGENIZATION OF MARINE ECOSYSTEMS AFTER THE END-PERMIAN MASS EXTINCTION

Biotic homogenization— the increased taxonomic similarity across ecosystems— has been observed across global terrestrial and marine ecosystems after the end-Permian mass extinction, but its causes remain debated. Here, we compare fossil similarity patterns with predictions from a metabolic model of animal habitat constrained by species trait data and forced by paleoclimate simulations of ocean warming and O₂ loss to determine whether biotic homogenization can be explained by the physiological tolerance of the surviving biota to the hyperthermal and hypoxic habitats of Early Triassic oceans. In a global grid of equal-area hexagonal cells containing >20 fossil occurrences downloaded from the Paleobiology Database (1,786 occurrences of 246 genera), we quantified changes in community similarity of bivalves and gastropods spanning the Changhsingian (~254.4 – 251.9 Ma) and Induan (~251.9 -251.2 Ma) ages using three measures of taxonomic similarity: Biogeographic Connectedness, Jaccard Similarity and Czekanowski’s coefficient, each of which measures the degree of taxonomic similarity on a scale from 0 (endemic) to 1 (globally widespread). We find an increase in similarity in the Induan that is much larger than the difference between victims and survivors prior to extinction, suggesting that survivors became further homogenized. This homogenization signal is reproduced in the model simulations where it arises from the expansion of hypoxia and heat tolerant survivors from the tropics into warm, low-oxygen waters as these conditions become globally widespread. Thus, taxonomic homogenization of the post-extinction ocean can be interpreted as an individualistic response to physiologically viable habitat and does not require ecological release following taxonomic losses.