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.

自然形成的骨骼遗骸时间平均堆积物——即死亡集合体（death assemblages）——尽管时间分辨率较低，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错配情况，通常能够指示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，开展现生-死亡错配作为人类压力指示物的测试。我们在巴哈马群岛沿人类人口密度梯度选取的三座岛屿上，对10个人类压力水平相对较低的湖泊的现生群落与死亡集合体的相似性，与11处物理环境可比、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-死亡相似性进行了对比。研究发现，未受干扰湖泊的现生-死亡匹配度始终极佳，这表明利用死亡集合体开展现代与古湖沼生物多样性评估具备良好前景。在多数物理环境相似的配对湖泊对比中，受压力湖泊的样本级现生-死亡错配在物种分类组成与物种等级丰度两方面的平均水平均显著更高；受压力湖泊的样本并非均表现出更低的现生-死亡匹配度，但其匹配度的变异性更强。当将样本合并以开展湖泊级与岛屿级对比时，受压力湖泊仍表现出更低的现生-死亡匹配度，但与未受干扰湖泊的差异显著性有所降低——仅在单一样本中仅见死亡个体（或仅见现生个体）的物种，很可能在其他样本中以现生个体（或死亡个体）的形式存在。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符，但二者并无显著相关性；这一现象源于压力施加的时间、强度以及灾后恢复程度存在异质性。因此，介形类集合体的现生-死亡错配可作为样本级人类活动影响的可靠指示物，有望成为识别受干扰生境、乃至监测生境恢复进程的普适性工具。