ECOLOGICAL DYNAMICS AS INDICATORS OF RECOVERY FROM THE PERMIAN-TRIASSIC MASS EXTINCTION

Recovery from mass extinction is the return of the biosphere to a pre-extinction state, but the biosphere and its ecological systems may be described in multiple ways. Restructuring, which signifies that post-extinction systems may differ dramatically from pre-extinction systems, also requires metrics comparing pre- and post-extinction states, as well as distinction from the restructuring that occurs during other intervals from ongoing taxon origination, evolutionary innovation, and background extinction. Biotic recovery is generally measured with taxon richness, morphological diversity/disparity, functional diversity, community structure, or ecological dynamics. If these parameters are highly variable prior to a mass extinction, then the only indicator of recovery is taxon richness, since it is the only measure of extinction. If, however, parameters were stationary prior to the extinction, then one may develop multiple metrics of restructuring and recovery.

Ongoing study of Permian-Triassic terrestrial paleoecosystems of the South African Karoo Basin (Roopnarine and Angielczyk, 2012) have shown that prior to the Permian-Triassic extinction (PTME), community dynamics were optimally stable, and resistant to perturbations of primary production. Communities during the PTME, which suffered severe taxon losses, became even more resilient, but less resistant. Taxon richness recovered rapidly during the earliest Triassic, but paleocommunities were neither optimally stable nor resistant. Both stability and resistance, however, were equivalent to pre-PTME communities by the Middle Triassic. Taxon diversification and ecological function were therefore uncoupled in the aftermath, but both PTME recovery and restructuring can be defined relative to a stable, pre-extinction Permian dynamics.

Roopnarine, P. D. and K. D. Angielczyk. 2012. The evolutionary palaeoecology of species and the tragedy of the commons. Biology Letters 8:147-150