ECOLOGY OF THE EARLY TRIASSIC POST-EXTINCTION WORLD (Invited Presentation)

Marine faunas that thrived in the wake of the end-Permian mass extinction event were unusual in many aspects. In comparison to background times, species were geographically more cosmopolitan and ecologically more eurytopic, and some clades failed to radiate in spite of a largely vacated niche space, whereas others rediversified quickly. The standard explanation for these unusual features has been the presence of environmental stress, but evidence for this idea remained equivocal. Recent work argues instead that many unusual aspects of Early Triassic marine biota are predicted by ecological theories on competition, niche partitioning, niche construction, and predator-prey interaction. Accordingly, geographic distribution and eurytopy/stenotopy responded to changes in the level of interspecific competition, as did niche partitioning and rates of diversification. More precisely, reduced levels of interspecific competition after elimination of ca. 90 % of marine species allowed surviving species to exploit the full range of their fundamental niches until new competitors evolved, and systematic differences between clades in the intensity of competition account for discrepancies in the pace of their recovery (e.g., quick recovery of ammonoids versus delayed recovery of bivalves). The effect of niche construction on diversification is exemplified by the Anisian resurgence of reef communities, which contributed to the steep increase in benthic diversity during the Middle Triassic. Finally, predator-prey escalation during the Mesozoic marine revolution stimulated morphological and thus taxonomic diversification, and increasing intensity of predation pushed populations of prey animals below the carrying capacities, which allowed the co-existence of competing taxa. A diversification model that incorporates these aspects of ecological theory is proposed, which combines (1) a hyperbolic term for the early phase of rediversification with (2) a damping term for systems near their carrying capacities. Predictions of this model are in surprisingly precise accordance with empirical data on the rediversification after the end-Permian and other mass extinction events.