Data from: On the benefits of being redundant: low compositional fidelity of diatom death assemblages does not hamper the preservation of environmental gradients in shallow lakes

Comparisons between death assemblages and their source living communities are among the most common actualistic methods of evaluating the preservation of compositional and environmental information in fossil assemblages. Although live-dead studies have commonly focused on marine mollusks, the potential of diatoms to preserve ecological information in continental settings has been overlooked. Thus, little is known about the nature and magnitude of the taphonomic biases affecting live-dead agreement of diatom assemblages, despite their extensive application as modern and fossil bioindicators in paleoecological and paleoenvironmental reconstructions. In this study, I analyzed three live-dead data sets in order to evaluate the compositional and environmental fidelity exhibited by diatom death assemblages in shallow lakes. I find that diatom death assemblages (DAs) do differ significantly in their taxonomic composition from living assemblages (LAs), mainly as a consequence of (1) differences in the temporal resolution between time-averaged DAs and non-averaged LAs, and (2) differential preservation of diatom taxa related to the intrinsic properties of their valves. Despite compositional dissimilarities, DAs were able to capture the same environmental gradients as LAs, with high significance. This decoupling between live-dead agreement in community composition and community response to gradients can be related to the existence of at least two mutually exclusive subsets of species that significantly captured compositional dissimilarities based on the full set of the species in the three lakes. This functional redundancy implies that the between-sample relationships of living assemblages can be significantly preserved by DAs even if some taxa are removed by taphonomic processes. The preservation of environmental gradients thus does not require good preservation of all living taxa. Structural redundancy compensates for the loss of compositional fidelity caused by postmortem processes in the diatom data set.

死亡组合（death assemblages）与其原生现生群落之间的对比，是评估化石组合中组成与环境信息保存效果的最常用现实主义研究方法之一。尽管现生-死亡研究（live-dead studies）通常以海洋软体动物为主要研究对象，但硅藻在陆相环境中保存生态信息的潜力却长期被忽视。尽管硅藻作为现代与化石生物指标被广泛应用于古生态与古环境重建，但人们对影响硅藻组合现生-死亡一致性的埋藏偏差（taphonomic biases）的性质与程度仍知之甚少。本研究共分析三套现生-死亡数据集，旨在评估硅藻死亡组合（diatom death assemblages, DAs）在浅湖环境中所表现出的组成与环境保真度（fidelity）。研究结果显示，硅藻死亡组合的分类学组成与现生组合（living assemblages, LAs）存在显著差异，这主要由两方面因素导致：其一，经时间平均（time-averaged）的死亡组合与未经时间平均的现生组合之间存在时间分辨率差异；其二，不同硅藻类群的保存差异与其壳瓣的固有特性直接相关。尽管二者在组成上存在差异，但硅藻死亡组合仍能精准捕捉到与现生组合一致的环境梯度（environmental gradients），且相关性具有极高的统计学显著性。群落组成的现生-死亡一致性与群落对环境梯度的响应之间的这种解耦现象，可归因于至少两个互斥的物种子集的存在——基于三个湖泊的全部物种数据集，这两个子集能够显著捕捉到组成层面的差异。这种功能冗余（functional redundancy）表明，即便部分类群因死后过程（postmortem processes）遭到移除，硅藻死亡组合仍能显著保留现生组合的样间关系。由此可见，环境梯度的保存并不要求所有现生类群都得到完好保存。结构冗余能够补偿硅藻数据集因死后过程所导致的组成保真度损失。