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

在我们进入被称为“第六次大灭绝”的生物多样性危机之际，彻底了解灭绝事件从未像现在这样重要。但是，我们真的在走向大灭绝吗？当前的事件与地质历史上的灾难性生物危机相比又如何呢？地质记录为研究快速气候变化下的生态系统动态和崩溃提供了丰富的信息，了解这些事件可能是帮助预测人为变暖对现有和未来海洋生态系统影响的关键。一个悬而未决的灭绝问题是，为什么古生代和中生代的快速变暖事件总是引发大规模灭绝，而新生代类似的极端气候事件却没有？一种解释这种不匹配的观点认为，现代生态系统结构是在白垩纪-古近纪大灭绝（66 Ma）之后的早期新生代建立的，而新生代大灭绝缺乏的原因在于现代海洋生态系统的鲁强性增强。然而，关于灭绝的古生物学研究目前缺乏关于生态系统内生物如何相互作用的关键信息来源。从当代生态学研究中我们知道，生物之间的相互作用在现代生态系统的结构、功能和恢复能力中起着关键作用。因此，如果不能很好地理解群落内的生物相互作用，就很难解释大灭绝事件中物种灭绝和生态系统崩溃的动态。CASCaDE将通过一种新颖的、跨学科的方法，结合生态学建模和古生物学的最新进展，推动灭绝古生物学的根本性变化。具体来说，我们将测试海洋生态系统的稳健性和稳定性（这是由食物网中捕食者/猎物的相互作用决定的）在确定气候引发的灭绝级联的脆弱性方面的作用。我们将调查地质记录中全球快速变暖的各个时期——其中一些引发了大规模物种灭绝，而另一些则没有。我们将使用计算机建模方法来模拟几种假设的灭绝情景，这些情景发生在气候变化事件发生之前的化石生态系统上。这些情景将发展成与快速温室变暖有关的已知环境压力，即海洋温度上升、海洋缺氧和海洋酸化。然后，我们将测试哪种假设的灭绝情景最能预测事件后的生态系统结构。具体来说，我们将验证古生代/中生代和新生代食物网结构和生态系统恢复能力的差异与极端气候条件的相互作用不同，导致古生代和中生代而不是新生代的生态系统大规模崩溃的假设。我们还将探讨与不同化石保存潜力相关的食物网重建的不确定性如何影响我们的预测。CASCaDE的目标是通过模拟古代生态系统内的生物相互作用，以及基于遥远过去的极端气候事件和大规模物种灭绝，对现代海洋生态系统快速变暖的灭绝风险进行预测，将定量古生物学和保护生物学推向新的领域。我们将把过去气候变化灭绝级联最可能的情景应用于现代海洋生态系统的食物网，以预测人为的全球变暖是否有可能引发古生代/中生代水平的大规模灭绝级联，或者新生代生态系统稳健性的增强是否会缓冲海洋生态系统的完全崩溃。

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.