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Extinction resistance in prehistoric food webs

Extinction resistance in prehistoric food webs. A bottom-up model. What effect does the structure of food webs have on their stability?. Ancient communities with a large population of carnivores Modern communities with mainly herbivores

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Extinction resistance in prehistoric food webs

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  1. Extinction resistance in prehistoric food webs A bottom-up model

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

  3. The model

  4. C2 guild C1 guild

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

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

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

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

  9. Effect of connectance • Greater number of connections in Lystrosaurus communitiesmay have amplified secondary effects

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

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

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