Dunne Jennifer A, Williams Richard J, Martinez Neo D, Wood Rachel A, Erwin Douglas H
Santa Fe Institute, Santa Fe, New Mexico, United States of America.
PLoS Biol. 2008 Apr 29;6(4):e102. doi: 10.1371/journal.pbio.0060102.
A rich body of empirically grounded theory has developed about food webs--the networks of feeding relationships among species within habitats. However, detailed food-web data and analyses are lacking for ancient ecosystems, largely because of the low resolution of taxa coupled with uncertain and incomplete information about feeding interactions. These impediments appear insurmountable for most fossil assemblages; however, a few assemblages with excellent soft-body preservation across trophic levels are candidates for food-web data compilation and topological analysis. Here we present plausible, detailed food webs for the Chengjiang and Burgess Shale assemblages from the Cambrian Period. Analyses of degree distributions and other structural network properties, including sensitivity analyses of the effects of uncertainty associated with Cambrian diet designations, suggest that these early Paleozoic communities share remarkably similar topology with modern food webs. Observed regularities reflect a systematic dependence of structure on the numbers of taxa and links in a web. Most aspects of Cambrian food-web structure are well-characterized by a simple "niche model," which was developed for modern food webs and takes into account this scale dependence. However, a few aspects of topology differ between the ancient and recent webs: longer path lengths between species and more species in feeding loops in the earlier Chengjiang web, and higher variability in the number of links per species for both Cambrian webs. Our results are relatively insensitive to the exclusion of low-certainty or random links. The many similarities between Cambrian and recent food webs point toward surprisingly strong and enduring constraints on the organization of complex feeding interactions among metazoan species. The few differences could reflect a transition to more strongly integrated and constrained trophic organization within ecosystems following the rapid diversification of species, body plans, and trophic roles during the Cambrian radiation. More research is needed to explore the generality of food-web structure through deep time and across habitats, especially to investigate potential mechanisms that could give rise to similar structure, as well as any differences.
关于食物网——栖息地内物种间捕食关系的网络，已经形成了大量基于实证的理论。然而，古代生态系统缺乏详细的食物网数据和分析，这主要是因为分类单元分辨率低，以及捕食相互作用的信息不确定且不完整。对于大多数化石组合来说，这些障碍似乎是无法克服的；然而，一些在营养级上具有出色软躯体保存的组合是食物网数据编纂和拓扑分析的候选对象。在这里，我们展示了寒武纪时期澄江生物群和布尔吉斯页岩生物群看似合理的详细食物网。对度分布和其他结构网络属性的分析，包括对寒武纪饮食指定相关不确定性影响的敏感性分析，表明这些古生代早期群落与现代食物网有着显著相似的拓扑结构。观察到的规律反映了结构对食物网中分类单元数量和联系的系统依赖性。寒武纪食物网结构的大多数方面都可以通过一个简单的“生态位模型”很好地描述，该模型是为现代食物网开发的，并考虑了这种尺度依赖性。然而，古代和现代食物网在拓扑结构上存在一些差异：在早期的澄江食物网中，物种之间的路径长度更长，捕食环中的物种更多，并且两个寒武纪食物网中每个物种的联系数量变化更大。我们的结果对排除低确定性或随机联系相对不敏感。寒武纪和现代食物网之间的许多相似之处表明，后生动物物种之间复杂捕食相互作用的组织存在令人惊讶的强大且持久的限制。少数差异可能反映了在寒武纪辐射期间物种、身体结构和营养角色快速多样化之后，生态系统中向更强整合和受限的营养组织的转变。需要更多研究来探索食物网结构在漫长时间和不同栖息地的普遍性，特别是要研究可能产生相似结构以及任何差异的潜在机制。
