NERC-NSFGEO Community And Structural Collapse During Mass Extinctions (CASCaDE)

A thorough understanding of extinction events has never been more important as we are entering a biodiversity crisis that is being heralded as the "Sixth Mass Extinction". But are we really heading for a mass extinction and how will this current event compare to the catastrophic biotic crises of the geological past? The geological record provides a wealth of information for studying ecosystem dynamics and collapse under rapid climate change and understanding these events may be key in helping to predict the consequences of anthropogenic warming for existing and future marine ecosystems. One great unanswered extinction question is why do rapid warming events of the Palaeozoic and Mesozoic consistently trigger mass extinction whereas similarly extreme climatic events of the Cenozoic do not? An argument put forward to explain this mismatch is that modern ecosystem structure was established in the early Cenozoic in the aftermath of the Cretaceous-Paleogene mass extinction (66 Ma) and that the reason for the lack of Cenozoic mass extinctions lies in the increased robustness of modern marine ecosystems. However, palaeobiological studies of extinction currently lack critical sources of information about how organisms interact with one another within ecosystems. We know from contemporary ecological studies that interactions between organisms play a pivotal role in the structure, function and resilience of modern ecosystems. Therefore, it makes it very difficult to interpret the dynamics of extinctions and ecosystem collapse across mass extinction events without a good understanding of the biotic interactions within communities.

CASCaDE will drive a fundamental change in extinction palaeobiology via a novel and cross-disciplinary approach combining recent advances in ecological modelling with palaeontology. Specifically, we will test the role of marine ecosystem robustness and stability (which is determined by predator/prey interactions in food webs) in determining vulnerability to climate-triggered extinction cascades. We will investigate various periods of rapid global warming in the geological record - some that triggered mass extinction and others that did not. We will use a computer modelling approach to simulate several hypothetical extinction scenarios on fossil ecosystems pre-dating the climatic change events. These scenarios will be developed to represent known environmental stresses associated with rapid greenhouse warming i.e. rise in ocean temperature, ocean anoxia, and ocean acidification. We will then test which hypothetical extinction scenario best predicts post-event ecosystem structure. Specifically, we will test the hypothesis that differences in Palaeozoic/Mesozoic and Cenozoic food web structure and ecosystem resilience interacted with extreme climatic conditions differently leading to wholesale ecosystem collapse in the Palaeozoic and Mesozoic but not in the Cenozoic. We will also explore how uncertainty in the reconstruction of the food webs linked to varying fossil preservation potential might influence out predictions.

CASCaDE aims to push quantitative palaeobiology and conservation biology into new territory via modelling biotic interactions within ancient ecosystems and enabling predictions of extinction risk to rapid warming in modern marine ecosystems based upon extreme climatic events and mass extinctions in the distant past. We will apply the most likely scenarios of past climate change extinction cascades to food webs from modern marine ecosystems in order to predict whether anthropogenic global warming is likely to trigger Palaeozoic/Mesozoic-level mass extinction cascades or whether increased Cenozoic ecosystem robustness will buffer the oceans from complete ecosystem collapse.