Abstract
We modelled the resilience and transient dynamics of terrestrial paleocommunities from the Karoo Basin, South Africa, around the Permian-Triassic mass extinction. Using recently refined biostratigraphic data that suggest two pulses of extinction leading up to the Permian-Triassic boundary, we show that during times of low extinction, paleocommunities were no more stable than randomly assembled communities, but they became more stable during the mass extinction. Modelled food webs before and after the mass extinction have lower resilience and less stable transient dynamics compared to random food webs lacking in functional structure but of equal species richness. They are, however, more stable than random food webs of equal richness but with randomized functional structure. In contrast, models become increasingly more resilient and have more stable transient dynamics, relative to the random models, as the mass extinction progressed. The increased stability of the community that resulted from the first pulse of extinction was driven by significant selective extinction against small body-sized amniotes, and significantly greater probabilities of survival of large bodied amniotes. These results suggest that although communities during times of background extinction could have been more stable given alternative patterns of functional diversity, those during the mass extinction were more stable than any alternative possibilities.