Quantitative analyses of Ediacaran Ecosystems

生物体至少在过去的35亿年里占据了地球，但直到最近，它们的化石残骸才足够大，足以用肉眼看到。第一批合适的宏观化石出现在大约5.8亿年前，也就是埃迪卡拉纪中期，不到5000万年前，可识别的动物和贝壳、骨骼和洞穴的传统化石记录就出现了。埃迪卡拉纪化石记录的意义在于，它直接描述了从最初30亿年完全是微生物的世界过渡到明显姗姗来迟的现代生物圈的建立。不幸的是，埃迪卡拉人的记录也存在严重问题。我们不仅不知道这些最早的大型生命形式与什么有关，甚至不知道它们是什么类型的东西，或者它们是如何谋生的。这项研究的目的是重建这些化石的原始群落生态-它们如何相互作用以及如何与环境相互作用-着眼于了解它们在现代世界中的作用。研究埃迪卡拉纪大型化石的优势之一是它们在生活中不会移动，因此它们的化石位置提供了它们最初的空间相互关系的准确描述。通过分析这些空间数据，有可能提取出数量惊人的原始生态细节。就像森林中的树木一样，埃迪卡拉化石在床层表面的分布反映了许多影响的相互作用，包括生物生活史、物种间的竞争和促进以及物理环境。因此，可以使用现代森林生态学家开发的许多复杂的统计和建模技术对这些生态过程进行反向工程。我们已经在最近的《自然》杂志上发表了一篇论文，展示了这种方法的潜力，现在计划将其系统地应用于已知的最早的埃迪卡拉纪宏化石--“阿瓦隆组合”--几乎完全从查恩伍德森林、莱斯特郡和纽芬兰东南部的标志性遗迹中获知。研究计划分为两个主要部分。首先是数据收集。在这里，我们计划汇编一个全面的数据库，其中包括所有已知的阿瓦隆地层表面的高分辨率、数字化的3D图像，以保存大量的大型化石(&gt；100个标本)。由于最近激光扫描技术的进步，这将得出44个独立的层理群落中约20,000个化石的准确大小、位置和方向。该项目的第二个也是主要的重点是分析这些数据的主要生态内容。使用一系列互补的定量技术，我们计划解决早期埃迪卡拉生态学中的三个主要问题：1)这些有机体如何与他们的环境相互作用，以及这些环境相互作用与有机体繁殖相比有多重要？这是现代群落生态学中长期争论的主题，而埃迪卡拉人的记录为第一大生物之间的平衡提供了独特的观点。2)埃迪卡拉人生态系统中身体大小的分布是什么，是什么生态过程导致了它们特殊的大小结构？在现代水生系统中，身体大小与捕食和动物的摄食关系直接相关，但在这些早期的宏观群落中，没有证据表明有捕食动物。3)上覆水柱内对资源的竞争是否主导了阿瓦隆生物之间的相互作用？这经常被认为是埃迪卡拉生态中的一个重要因素，但从未进行过定量测试。我们对埃迪卡拉生态的这一问题和其他问题的分析方法有望为现代生物圈的起源提供重要的新线索。

Organisms have occupied the planet for at least the past 3.5 billion years, but only relatively recently have their fossil remains been large enough to see with the naked eye. The first properly macroscopic fossils turn up around 580 million years ago, in the middle of the Ediacaran Period, less than 50 million years before the appearance of recognizable animals and the conventional fossil record of shells, bones and burrows. The significance of the Ediacaran fossil record is that is provides a direct account of the transition from the exclusively microbial world of the first three billion years, to the conspicuously belated establishment of a recognizably modern biosphere. Unfortunately, the Ediacaran record is also profoundly problematic. Not only do we not know what these earliest large life-forms were related to, it is not even clear what kinds of things they were, or how they made a living. The aim of this research proposed here is to reconstruct the original community ecology of these fossils - how they interacted with one another and with their environment - with an eye to understanding their role in bringing about the modern world.One of the advantages of studying Ediacaran macrofossils is that none of them moved during life, so their fossilized positions provide an exact account of their original spatial inter-relationships. By analysing these spatial data, it is possible extract a surprising amount of original ecological detail. Like trees in a forest, the distribution of Ediacaran fossils on bedding surfaces reflects the interplay of numerous effects including organism life-history, inter-specific competition and facilitation, and the physical environment. As such, these ecological processes can be reverse engineered using many of the sophisticated statistical and modelling techniques developed by modern forest ecologists. We have already demonstrated the potential of this approach with a recent paper in Nature, and now plan to apply it systematically to the earliest known Ediacaran macrofossils, the "Avalonian assemblage" - known almost exclusively from iconic occurrences in Charnwood Forest, Leicestershire and SE Newfoundland. The research programme is divided into two main parts. The first is data collection. Here we plan to assemble a comprehensive database of high-resolution, digitized 3D images of all known Avalonian bedding surfaces preserving large populations (> 100 specimens) of macrofossils. Made possible by recent advances in laser-scanning technology, this will yield the precise size, position and orientation of ~20,000 fossils comprising 44 separate bedding-surface communities. The second, and primary, focus of this project is to analyse these data for their primary ecological content. Using a range of complementary quantitative techniques, we plan to address three main issues in early Ediacaran ecology:1) How did these organisms interact with their environment, and how much did these environmental interactions matter compared to organism reproduction? This is the subject of a longstanding debate in modern community ecology, and the Ediacaran record offers a unique view of the balance among the first large organisms.2) What was the distribution of body-sizes in Ediacaran ecosystems and what ecological processes were responsible for their particular size-structure? In modern aquatic systems, body-size is directly related to predation and the feeding relationships of animals, but there is no evidence of predatory animals in any of these early macroscopic communities. 3) Did competition for resources within the overlying water-column dominate interactions between Avalonian organisms? This has often been promoted as a significant factor in Ediacaran ecology, but has never been quantitatively tested. Our analytical approach to this and other questions of Ediacaran ecology promise to shed significant new light on the origin of the modern biosphere.