Predator-prey interactions amongst Permo-Triassic terrestrial vertebrates as a deterministic factor influencing faunal collapse and turnover.

Unlike modern mammalian communities, terrestrial Paleozoic and Mesozoic vertebrate systems were characterized by carnivore faunas that were as diverse as their herbivore faunas. The comparatively narrow food base available to carnivores in these paleosystems raises the possibility that predator-prey interactions contributed to unstable ecosystems by driving populations to extinction. Here, we develop a model of predator-prey interactions based on diversity, abundance and body size patterns observed in the Permo-Triassic vertebrate fossil record of the Karoo Basin, South Africa. Our simulations reflect empirical evidence that despite relatively high carnivore: herbivore species ratios, herbivore abundances were sufficient for carnivores to maintain required intake levels through most of the Karoo sequence. However, high mortality rates amongst herbivore populations, even accounting for birth rates of different-sized species, are predicted for assemblages immediately preceding the end-Guadalupian and end-Permian mass extinctions, as well as in the Middle Triassic when archosaurs replaced therapsids as the dominant terrestrial fauna. These results suggest that high rates of herbivore mortality could have played an important role in biodiversity declines leading up to each of these turnover events. Such declines would have made the systems especially vulnerable to subsequent stochastic events and environmental perturbations, culminating in large-scale extinctions.