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.

骨骼遗骸的自然时间加权堆积——即死亡堆积（death assemblages）——可为多样生境中的群落物种组成与结构提供可靠但时间分辨率较低的信息；其与本地现生群落的错配通常可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，验证死亡-现生群落错配（live-dead mismatch）作为人类压力指标的可行性。我们在巴哈马群岛沿人类人口密度梯度选取三座岛屿，对比了10个人类压力水平较低的湖泊的现生群落与死亡堆积的相似性，以及11个物理环境相近、曾或正受工业、农业或其他人类活动影响的湖泊的死亡-现生相似性。研究发现，未受干扰的原始湖泊的死亡-现生群落匹配度始终极佳，这表明利用死亡堆积开展现代及古湖沼学的（paleolimnological）生物多样性评估具备良好应用前景。在多数物理环境匹配的配对湖泊对比中，受干扰湖泊的样本级分类组成与物种等级丰度的死亡-现生错配程度平均显著更高；受干扰湖泊并非所有样本的匹配度均低于原始湖泊，但其匹配度的变异性更强。当将样本按湖泊尺度与岛屿尺度合并分析时，受干扰湖泊的死亡-现生匹配度仍更低，但与原始湖泊的差异显著性有所降低——仅在死亡样本中出现（或仅在现生样本中出现）的物种，大概率会在其他样本中以现生（或死亡）形式出现。不同岛屿间的死亡-现生匹配度差异与人口密度差异趋势一致，但未呈现显著相关性，这源于人类压力的作用时间、强度异质性，以及灾后恢复程度的差异。由此可见，介形类群落的死亡-现生错配可作为样本尺度上可靠的人类影响指标，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。