Data from: Testing for human impacts in the mismatch of living and dead ostracode assemblages at nested spatial scales in subtropical lakes from the Bahamian archipelago

Naturally time-averaged accumulations of skeletal remains – death assemblages – provide reliable, albeit temporally coarse, information on the species composition and structure of communities in diverse settings, and their mismatch with local living communities usually signals recent human-driven ecological change. Here, we present the first test of live-dead mismatch as an indicator of human stress using ostracodes. On three islands along a gradient of human population density in the Bahamas, we compared the similarity of living and death assemblages in ten lakes with relatively low levels of human stress to live-dead similarity in eleven physically comparable lakes subject to industrial, agricultural, or other human activities currently or in the past. We find that live-dead agreement in pristine lakes is consistently excellent, boding well for using death assemblages in modern-day and paleolimnological biodiversity assessments. In most comparison of physically-similar paired lakes, sample-level live-dead mismatch in both taxonomic composition and species’ rank-abundance is on average significantly greater in the stressed lake; live-dead agreement is not lower in all samples from stressed lakes, but is more variable. When samples are pooled for lake-level and island-level comparisons, stressed lakes still yield lower live-dead agreement but the significance of the difference with pristine lakes decreases – species that occur dead-only (or alive-only) in one sample are likely to occur alive (or dead) in other samples. Inter-island differences in live-dead agreement are congruent with, but not significantly correlated with, differences in human population density. This situation arises from heterogeneity in the timing and magnitudes of stresses and in the extent of post-stress recovery. Live-dead mismatch in ostracode assemblages thus may be a reliable indicator of human impact at the sample-level with the potential to be a widely-applicable tool for identifying impacted habitats, and perhaps, monitor the progress of their recovery.自然形成的时间平均骨骼遗骸堆积——即死亡组合（death assemblages）——尽管在时间分辨率上较为粗糙，但仍能为多样生境下的群落物种组成与结构提供可靠信息；其与本地现生群落的不匹配现象，通常指示了近期人类活动驱动的生态变化。本研究首次以介形类（ostracodes）为研究对象，将现生-死亡不匹配作为人类胁迫的指示指标开展检验。我们选取巴哈马群岛中沿人类人口密度梯度分布的三座岛屿，对10个人类胁迫程度较低的湖泊的现生组合与死亡组合的相似度，与11处环境特征相近但当前或历史上曾受工业、农业或其他人类活动影响的湖泊的现生-死亡组合相似度进行了对比。研究发现，未受干扰的原始湖泊中的现生-死亡匹配度始终极佳，这表明利用死亡组合开展现代与古湖沼生物多样性评估具有良好可行性。在多数环境匹配的成对湖泊对比中，受胁迫湖泊在物种组成与物种等级丰度层面的样本级现生-死亡不匹配度平均显著更高；并非所有受胁迫湖泊的样本的现生-死亡匹配度都更低，但其波动幅度更大。当将样本合并以开展湖泊级与岛屿级对比时，受胁迫湖泊的现生-死亡匹配度仍低于原始湖泊，但二者差异的显著性有所降低——仅在某一样本中出现死亡个体（或仅现生个体）的物种，很可能在其他样本中表现为现生（或死亡个体）。不同岛屿间的现生-死亡匹配度差异与人类人口密度差异相一致，但二者并无显著相关性；这一现象源于胁迫发生的时间、强度以及胁迫后恢复程度的异质性。因此，介形类组合的现生-死亡不匹配度可作为样本级人类活动影响的可靠指示指标，有望成为识别受干扰生境并监测其恢复进程的通用工具。