ECO-EVOLUTIONARY DYNAMICS AND COMMUNITY RESPONSE, RECOVERY AND REPLACMENT DURING AND AFTER THE PERMIAN-TRIASSIC MASS EXTINCTION IN THE KAROO BASIN, SOUTH AFRICA

Biological communities are assemblages of interacting species, where species properties and functional organization permit the stable coexistence and persistence of species, a condition termed “global stability”. Mass extinctions disrupt global stability by reducing the number of species and altering functional organization. The manner in which stability changes during a mass extinction and subsequent ecological recovery, restructuring or replacement, is therefore a function of external drivers and evolutionary dynamics filtered through this ecological structure. We show this by modeling the global stability of 10 successive terrestrial paleocommunities during the Permian-Triassic mass extinction (PTME) in the Karoo Basin, South Africa. Each community was modeled across a range of species ecological and life history properties, and interspecific trophic interactions.

Each paleocommunity was characterized by taxon richness S, partitioning of S among functional groups G, the number and pattern of interactions among functional groups, and number of interspecific trophic interactions. Species populations were modeled as dynamic exponential maps, and stability measured after communities of species attained metastable states. Community stability was then described by the extent to which each of those structural features altered the dynamics of random communities of equal S. Communities were compared to fully random communities, communities of equal S and G but randomized structural patterns, and communities of equal S and G but partitioned differently. Results show that global stability increased significantly during the PTME, declined significantly in the E. Triassic, and reached a maximum in the M. Triassic. The implications are that: (1) Species during the PTME could have adapted to changing conditions with minimal impact on global stability; (2) community structure played little role in dynamics during the E. Triassic; (3) E. Triassic species properties could not vary broadly without reducing global stability; and (4) despite E. Triassic increases of taxon richness, ecological recovery was not attained until the M. Triassic.