Extinction resistance in prehistoric food webs A bottomup

Extinction resistance in prehistoric food webs A bottom-up model

What effect does the structure of food webs have on their stability? u Ancient communities with a large population of carnivores u Modern communities with mainly herbivores u Do models of such communities show a difference in the amount of extinction when perturbed?

The model

C 2 guild C 1 guild

Why a bottom-up approach? u Biodiversity crises involved declines in primary production: end-Permian and Cretaceous-Tertiary extinctions u Modern disruptions to biodiversity from the top of the food chain (e. g. , habitat loss) have not yet led to topdown extinction cascades u Bottom-up disturbances can lead to top-down effects

CEG model u CEG=Cascading Extinction on Graphs u Test resistance to disturbances – Remove primary producer, watch how secondary extinctions propagate through food web u Extinction when population size drops below a minimum viable population size

Results: community reaction to Wuchiapingian disruption Wordian Eodicynodon zone Wuchiapingian Cistecephalus zone Tapinocephalus Pristerognathus zone Tropidostoma zone P-Tr boundary Dicynodon zone Lystrosaurus zone Cynognathus zone

Lystrosaurus zone is different u Why such variability? u Presence of amphibians? – Feed at multiple trophic levels – Link between land water allows cascades to propagate – Larger feedback network

Effect of connectance u Greater number of connections in Lystrosaurus communities may have amplified secondary effects

Paradox of connectance? u Species with more connectance to others (more generalized in what they can eat) are more resistant to secondary extinction BUT u The large number of connections in the Lystrosaurus community may have contributed to instability

Selection for stable food web structure u Selection can act on food web as a whole u End-Permian mass extinction amphibian-dominated food web instability u Concentration of biomass in herbivores may lead to more stable communities