STRUCTURE AND FUNCTIONALITY: ANALYSIS OF THE TRIASSIC-JURASSIC FOOD WEB

Food webs describe the trophic relationships among diverse, co-occurring species in a community. They provide a useful quantitative framework for assessing ecological complexity and ecosystem responses to disturbance. While the effects of perturbations on communities have been studied extensively in extant ecosystems, more work needs to be done for paleoecological systems. Here we used food web analysis to understand the ecological impact of the end-Triassic mass extinction event (∼201.5mya) on the complexity and trophic organization of marine ecosystems. We built a Triassic-Jurassic food web dataset that includes 1903 marine taxa restricted to deposits in Europe spanning from the Rhaetian to Hettangian [~9my]. Trophic roles and the probable trophic relationships between taxa are assigned by autoecological analysis and from the literature, which were used to generate pre- and post-extinction food webs. The structure and complexity of these webs was compared to previously described extant and paleo food webs using cumulative degree distributions and various network structure properties (e.g., number of links, connectance, and proportion of predator, and basal taxa). Functional diversity and compositional turnover before and after the mass extinction event were estimated using functional richness and the Jaccard index. Differences in structural elements are observed through extinction event. ~53% of the species disappeared from the Rhaetian to Hettangian. Connectance decayed from 0.34 to 0.19, the number of link per species decreased ~45%, and the mean chain length shortened ~10%. The proportion of top species decreased significantly indicating a potential top-down cascading effect. Functional richness decreased ~50%, while filter feeders, predators, and herbivorous showed the highest dissimilarity. However, once changes in the size and complexity of the webs are considered, few aspects of trophic organization changed significantly across the extinction event, and the webs display fundamental network structure like other paleo and extant food webs. This suggests that the trophic organization of food webs is constant across the Phanerozoic, regardless the drastic effect of the mass extinctions like the end-Triassic that temporarily reduced ecological diversity and complexity.