FUNCTIONAL DIVERSITY OF THE MIDDLE TRIASSIC QINGYAN FORMATION, SOUTH CHINA: QUANTIFYING ECOLOGICAL RICHNESS AND EVENNESS IN MARINE PALEOCOMMUNITIES AFTER THE PERMO-TRIASSIC MASS EXTINCTION

The Permo-Triassic mass extinction (PTME), approximately 252 mya, was the largest biodiversity collapse in the Phanerozoic, resulting in reorganized and vastly altered marine communities during the Triassic. Recent studies have indicated that taxonomic and ecological diversity were decoupled following the PTME, indicating that while taxonomic diversity may recover quickly after an extinction event, true ecological restructuring may take much longer. As such, it is important to not only take into account the taxonomic diversity of a paleocommunity, but the functional diversity as well.

Results from our recent study that sampled several regional paleocommunities indicated that functional richness (i.e. number of functional groups) decreased to low levels in the immediate aftermath of the PTME. Functional richness steadily increased and reached high levels in the Middle Triassic. In contrast, functional evenness (i.e. distribution of abundance across functional groups) was found to be very high in all Early and Middle Triassic paleocommunities. High functional evenness contributes resilience to a community and protects it from abiotic and biotic perturbations. Therefore, we proposed that Triassic paleocommunities developed high functional evenness as a means to maintain stability and survival in the aftermath of the PTME.

Using field-collected data from the Middle Triassic (Anisian) Qingyan Formation in Guizhou Province, south China, we quantified both functional richness and evenness using a ten-trait ecospace model. Our results indicate that the Anisian Qingyan paleocommunity had high taxonomic and functional richness, as well as high functional evenness. This indicates that while the paleocommunity was in a later stage of restructuring, high functional evenness may have been present due to abiotic or biotic perturbations. These results further support the emerging pattern of variable levels of restructuring and functional diversity in different geographic regions following the PTME.