Stability, incumbency and ecological reorganization after the Permian-Triassic mass extinction

The Permian-Triassic mass extinction (PTME) altered macroevolutionary land-scapes by removing incumbent biota. Here, using terrestrial paleocommunities of the Karoo Basin spanning the PTME, we show that a pre-extinction incumbent configuration of biotic interactions made significant ecological re-organizations or macroevolutionary innovations unlikely. The post-PTME ecosystem initially was more likely to be reorganized, but incumbency was re-established by the Middle Triassic. We argue that the stability of the pre-PTME ecosystem, its subsequent loss, and replacement, resulted from the in-fluence of community-level structure and dynamics on species evolution and survival. One sentence summary Biotic incumbency at the end of the Paleozoic, based on community functional organization, was destroyed by the Permian-Triassic mass extinction, allowing the development of novel community types.