DO BIOTIC CONTROLS BUFFER AGAINST CLIMATE-DRIVEN EXTINCTION THREATS?

Both biotic and abiotic factors control diversification and extinction. Climate change, specifically temperature, is widely suggested as the main abiotic control on macroecology and macroevolution. Identifying biotic regulators of biodiversity change in deep time is more complex because we typically cannot directly observe biotic interactions. In taphonomic settings that preserve multiple individuals, we can make progress by reconstructing community dynamics. The spatially, biogeographically, and taxonomically comprehensive fossil record of Plio-Pleistocene planktic foraminifera allows high-resolution studies of long-term eco-evolutionary response.

Here we characterise assemblage diversity through the integration of richness, evenness, and dominance of taxa using Hill numbers to represent the effective number of species. We calculate Hill numbers for multiple individual species’ extinction events through the Plio-Pleistocene using abundance counts of planktic foraminiferal assemblages from tropical Atlantic ODP Site 925. We document changes in biodiversity structures across three intervals of pre-, imminent-, and post-extinction.

Using an Analysis of Covariance, we show differential relationships between climate states and extinction interval. There is a correlation at the reference Hill numbers for Shannon’s and Simpson’s Index (evenness and dominance, respectively) between those biodiversity metrics and climate state during the pre- and imminent-extinction phases, but not post-extinction. There is no correlation at any state for species richness. Our results suggest a decoupling from climate and thus a shift to less abiotic regulation on planktic foraminiferal assemblages post-extinction. While species richness is consistently lower post-extinction, the difference in dynamics between richness, evenness, and dominance calls into question the generality of reliance on taxon counts for inferring the regulators of biodiversity in deep time. With increased resolution, there is potential to gain understanding of how biotic forces shaped past extinctions to predict future extinctions under climate driven threats.