MODELING TERRESTRIAL FOOD WEB COLLAPSE IN THE END-PERMIAN EXTINCTION

The end-Permian extinction was the most severe mass extinction of the Phanerozoic, yet its causes remain mysterious. Here we use probabilistic food web models to explore how disruption of primary production (e.g., extinction of green plants) could have caused the collapse of end-Permian terrestrial ecosystems. First, we simulate food webs (trophic networks) reconstructed for the Dicynodon Assemblage Zone community of the Karoo Basin. Next, we perturb these food webs using simulated extinctions of taxa at varying levels of intensity, according to three modes of extinction: top-down, bottom-up, or uniform. This probabilistic forward model allows us to estimate the effects of such perturbations on terrestrial communities. We then use tree-based statistical methods (recursive partitioning) to estimate the intensity and mode of extinction from the actual extinction levels observed in Karoo Basin fauna. Our results suggest that the mode of extinction was bottom-up, implying that disruption of primary production was responsible for the collapse of late Permian terrestrial communities. Furthermore, relatively high levels of primary production loss are needed to account for observed levels of extinction among Karoo Basin consumers.