Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138;
Department of Earth and Environmental Sciences, Jonsson-Rowland Science Center, Rensselaer Polytechnic Institute, Troy, NY 12180.
Proc Natl Acad Sci U S A. 2018 May 15;115(20):5217-5222. doi: 10.1073/pnas.1719976115. Epub 2018 Apr 23.
Mass extinctions documented by the fossil record provide critical benchmarks for assessing changes through time in biodiversity and ecology. Efforts to compare biotic crises of the past and present, however, encounter difficulty because taxonomic and ecological changes are decoupled, and although various metrics exist for describing taxonomic turnover, no methods have yet been proposed to quantify the ecological impacts of extinction events. To address this issue, we apply a network-based approach to exploring the evolution of marine animal communities over the Phanerozoic Eon. Network analysis of fossil co-occurrence data enables us to identify nonrandom associations of interrelated paleocommunities. These associations, or evolutionary paleocommunities, dominated total diversity during successive intervals of relative community stasis. Community turnover occurred largely during mass extinctions and radiations, when ecological reorganization resulted in the decline of one association and the rise of another. Altogether, we identify five evolutionary paleocommunities at the generic and familial levels in addition to three ordinal associations that correspond to Sepkoski's Cambrian, Paleozoic, and Modern evolutionary faunas. In this context, we quantify magnitudes of ecological change by measuring shifts in the representation of evolutionary paleocommunities over geologic time. Our work shows that the Great Ordovician Biodiversification Event had the largest effect on ecology, followed in descending order by the Permian-Triassic, Cretaceous-Paleogene, Devonian, and Triassic-Jurassic mass extinctions. Despite its taxonomic severity, the Ordovician extinction did not strongly affect co-occurrences of taxa, affirming its limited ecological impact. Network paleoecology offers promising approaches to exploring ecological consequences of extinctions and radiations.
化石记录所记载的大规模灭绝为评估生物多样性和生态学随时间的变化提供了关键的基准。然而，在尝试比较过去和现在的生物危机时，会遇到困难，因为分类和生态变化是解耦的，尽管存在各种描述分类转变的指标，但尚未提出量化灭绝事件对生态影响的方法。为了解决这个问题，我们应用基于网络的方法来探索显生宙海洋动物群落的演化。化石共生数据的网络分析使我们能够识别相关古群落的非随机关联。这些关联，或进化古群落，在相对群落稳定的连续间隔中主导了总多样性。群落更替主要发生在大灭绝和辐射时期，当时生态重组导致一个关联的衰落和另一个关联的兴起。总的来说，除了与 Sepkoski 的寒武纪、古生代和现代进化动物群相对应的三个目级关联之外，我们在属和科的水平上还确定了五个进化古群落。在这种情况下，我们通过衡量地质时间内进化古群落的代表性变化来量化生态变化的幅度。我们的研究表明，奥陶纪大辐射事件对生态的影响最大，其次是二叠纪-三叠纪、白垩纪-古近纪、泥盆纪和三叠纪-侏罗纪大灭绝。尽管奥陶纪灭绝在分类上很严重，但它并没有强烈影响分类单元的共生，这证实了其有限的生态影响。网络古生态学为探索灭绝和辐射的生态后果提供了有前途的方法。
