COMPARING THE ECOLOGICAL DYNAMICS OF PERMIAN-TRIASSIC TETRAPOD COMMUNITIES FROM THE KAROO, LUANGWA, AND RUHUHU BASINS OF SOUTHERN AFRICA

The Permian-Triassic mass extinction (PTME) was a transformative event, marked by the extinction itself, the post-Permian transformation of surviving ecosystems, and the formation of new communities. The Karoo Basin of South Africa has served as the primary data source on the terrestrial extinction, but its global applicability is uncertain. Here we compare Permo-Triassic tetrapod communities of the Karoo to those from the Luangwa and Ruhuhu basins of Zambia and Tanzania (TZAM), respectively, analyzing their functional structures and simulating dynamic responses to environmental perturbation. We compiled data on species composition, body size, and hypothesized dietary preferences for each community, and reconstructed food webs using a simple set of rules for assigning taxa to guilds and specifying links between guilds. Community functional compositions were compared using nonmetric multi-dimensional scaling based on inter-community Jaccard distances and Bray-Curtis dissimilarity indices. We modeled paleocommunity dynamics with the Cascading Extinctions on Graphs (CEG) model, and fit nonlinear regression models to the results for inter-community comparisons. Results show that despite similar compositions, late Permian communities differed among the basins in their dynamics and resistance to secondary extinction: the TZAM communities showed lower resistance. The Karoo ecosystem displays evidence of a transformation to increased resistance during the late Permian. Although the Karoo ecosystem was reduced significantly by the PTME, structural features of that resistance persisted into the Early Triassic, facilitated by greater extinction susceptibility of small amniotes and large carnivorous amniotes. Resistance declined during the initial stages of post-extinction restructuring. Continued evolution of the Triassic ecosystem led to a recovery of resistance, but in a compositionally dissimilar community. The upper Lifua Member of the Manda Beds (Middle Triassic, Tanzania) was structurally distinct from the Karoo communities, but displayed similar dynamics. The recurrence and convergence of communities with different histories toward similar dynamics suggests that there are taxon-independent norms of community assembly and function operating on geological timescales.