Potential paleoecologic biases from size-filtering of fossils: Strategies for sieving
Potential paleoecologic biases from size-filtering of fossils: Strategies for sieving
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DOI：
10.2110/palo.2006.p06-002r
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发表时间：
2007-11-01
期刊：
影响因子：
1.6
通讯作者：
Daley, Gwen M.
中科院分区：
文献类型：
--
作者：
Bush, Andrew M.;Kowalewski, Michal;Daley, Gwen M.
从沉积物中提取化石的方法可以改变观察到的化石大小-频率分布，从而改变观察到的古生态模式。在先前工作的基础上，本研究使用虚拟筛分（即通过计算机上的次采样复制）来测试尺寸过滤对中新世软体动物数据库的表观生态组成的影响，其中测量了每个标本的尺寸。当模拟网格尺寸变化近一个数量级（2-10毫米）时，分层、运动和喂养类别的明显相对丰度在一些个体散装样品中发生了实质性变化。毫不奇怪，网目尺寸的变化对样本生态比例的影响程度部分取决于其尺寸-频率分布。如果目标是描述成虫群落的生态特征，所选择的网孔尺寸不应该太小，以至于幼虫占主导地位，也不应该太大，以至于大多数标本被排除在外。对于许多软体动物组合，2-4毫米通常是合适的。对于由异质收集的数据组成的预先存在的数据集，有一个积极的结果：将样本平均在一起以产生生态组成的平均视图往往会消除规模过滤偏见的更恶劣影响。因此，对单个样本的生态组成的比较可能对网目大小的影响很敏感，但对区域或全球动物群的比较可能更可靠，而且尺寸过滤的变化可能不会成为对生态空间利用进行大规模长期比较的障碍。利用生物量而不是丰度来衡量生态重要性，也通过减少小体个体对生态比例的影响，减少了网目尺寸偏差的影响。
The methods by which fossils are extracted from sediments can alter their observed size-frequency distributions, which can in turn alter observed paleoecologic patterns. Building on previous work, this study uses virtual sieving (i.e., replicated via subsampling on a computer) to test the effects of size filtering on the apparent ecologic composition of a database of Miocene mollusks in which the size of every specimen was measured. When simulated mesh sizes varied by nearly an order of magnitude (2-10 mm), the apparent relative abundances of tiering, motility, and feeding categories varied substantially in some individual bulk samples. Not surprisingly, the extent to which variations in mesh size affected the ecologic proportions of a sample depended in part on its size-frequency distribution. If the goal is to characterize the ecology of adult assemblages, the chosen mesh size should not be so small that juveniles dominate the results or so large that a majority of specimens are excluded. For many molluscan assemblages, 2-4 mm should often be appropriate. For preexisting data sets composed of heterogeneously collected data, there is a positive result: averaging samples together to produce a mean view of ecologic composition tends to remove the more egregious effects of the size-filtering bias. Thus, comparisons of the ecologic composition of single samples may be sensitive to mesh-size effects, but comparisons of regional or global faunas are likely more robust, and variations in size filtering may not be an obstacle to large-scale, secular comparisons of ecospace use. Measuring ecologic importance using biomass instead of abundance also reduced the effects of the mesh-size bias by reducing the influence of small-bodied individuals on ecologic proportions.