PERTURBATION RESISTANCE OF LATE MESOZOIC COMMUNITIES

To gain new insight into the dynamics that make certain ecosystems prone to collapse, and to test the hypothesis that community stability increased over time, we compiled food web data for four new Mesozoic terrestrial communities: the Moncure locality (Late Triassic, North America), Wessex Formation (Early Cretaceous, England), and Yixian Formation (Early Cretaceous, China) .We then subjected these communities, as well as 10 additional communities from the Carboniferous, Permian, and Triassic, to bottom-up perturbations using the Cascading Extinctions on Graphs (CEG) model. We quantified community stability by calculating the correlation between primary and secondary extinction levels, and the minimum and median levels of primary extinction needed for complete secondary extinction. The Moncure locality and the Wessex Formation resembled one another and most of the Permo-Carboniferous terrestrial communities (Moncure/Wessex values, respectively: rho: 0.85/0.78, min. primary extinction: 0.67/0.79, mean primary extinction: 0.91/0.95). The Yixian Formation showed very little secondary extinction for most perturbation levels, but a rapid, pulsed increase to total extinction (rho: 0.89, min. primary extinction: 0.74, mean primary extinction: 0.89). Even at high perturbation levels (0.9-1.0), the Yixian showed a more stable response with a significantly higher standard deviation of secondary extinction than the other communities. When combined with the results from the Paleozoic and Early-Middle Triassic communities, we found significant patterns relating the intensity of extinction at discrete perturbation levels (0.3 & 0.9) and the proportion of the community composed of strictly secondary consumers. This may indicate that increasing tetrapod herbivore diversity and abundance in Permian communities improved community perturbation resistance, a trend that continued in the Mesozoic following the interruption of the end-Permian extinction.