Mapping the Origin of Terrestrial Faunal Assemblages Using Strontium Isotopes

化石记录被用来加强我们对人口对气候变化反应的理解，并作为预测未来生态系统反应的指南。然而，到目前为止，对化石记录的解释是基于两个未经验证的假设。首先，在化石记录中看到的响应的空间尺度是众所周知的，特别是在陆地环境中，其次，群落随时间的变化代表了当地人口的变化，而不是采样面积的变化。皮斯·哈德利和佩坦提议通过分析锶的同位素组成来检验这些假设，锶同位素组成是来自黄石国家公园的丰富的化石骨骼序列。黄石公园的序列跨越了过去3000年，并被化石遗址附近的全面现代收藏所扩大。由于锶同位素不会被生物过程分馏，所以基岩和上覆土层的锶含量、从土壤中吸收锶的植物和消耗植物的动物将密切相关。采样点分布在一个不均匀的地质景观中，每个采样点都位于具有明显不同的87Sr/86Sr同位素特征的基岩之下。如果化石遗址代表了当地的收藏品，Hadly和Paytan预测，这两个组合将记录显著不同的锶同位素比率。相反，如果地点的收集半径很大，并包含区域平均锶价值，他们预计的价值与当地基岩大不相同(可能彼此更相似)。初步数据表明，这些化石组合具有不同的锶同位素组成，代表了当地的基岩。PIs将决定是否有可能既排除采集面积随时间的变化，又从统计上限制对给定地点进行生态、进化和古气候解释的规模。此外，PI们建议通过调查来自科罗拉多州中部落基山脉的中更新世动物群的样本来测试他们方法的一般性。拟议的研究的智力价值是什么？调查人员建议以一种新的方式确定动物对环境的使用范围。他们计划评估来自落基山脉三个地点的一系列化石地点随着时间的推移对栖息地的使用情况。在缺乏这种分析的情况下，采样偏差的空间成分在现代或古生物组合的大多数研究中都无法解释。这项分析将决定锶同位素在多大程度上可以被用作评估化石记录的生态保真度的工具。拟议的研究产生了什么更广泛的影响？这项研究的方法和结果将对有兴趣重建过去群落的古生物学家和有意了解生态系统功能的空间尺度的生态学家感兴趣。这项研究对进化论者、自然资源保护论者、地质学家和行为学家等其他专家也有意义。通过综合多个领域，整合不同领域、分析和统计方法，Hadly和Paytan强调研究生和本科生的跨学科培养。

ABSTRACTThe fossil record is being called upon to enhance our understanding of population responses to climate change and to serve as a guide for predicting ecosystem responses in the future. However, interpretations of the fossil record have heretofore been predicated on two untested hypotheses. First, that the spatial scale of the response seen in the fossil record, especially in terrestrial settings, is well understood, and second, that community change through time represents shifts in local populations rather than changes in sampling area. PIs Hadly and Paytan propose to test these hypotheses by analyzing the strontium isotopic composition a rich sequence of fossil bones from Yellowstone National Park. The Yellowstone sequences span the past 3000 years and are augmented by a comprehensive modern collection from the vicinity of the fossil sites. Because strontium isotopes are not fractionated by biological processes, the strontium content of the bedrock and overlying regolith, the vegetation that takes up strontium from the soil and the animals consuming the vegetation will be strongly related. The sampling localities are distributed across a heterogeneous geologic landscape, with each site underlain by bedrock with distinctly different 87Sr/86Sr isotopic signatures. If the fossil sites represent local collections, Hadly and Paytan predict that the two assemblages will record significantly different strontium isotope ratios. Conversely, they expect values much different from the local bedrock (and possibly more similar to each other) if the collecting radii of the sites are large and incorporate regional average strontium values. Preliminary data indicate that these fossil assemblages each have distinct Sr isotopic compositions representing the local bedrock. The PIs will determine whether it is possible both to rule out shifts in collection area through time and to constrain statistically the scale at which ecological, evolutionary, and paleoclimatic interpretations of a given site should be applied. Further, the PIs propose to test the generalities of their approach by investigation of samples from a middle Pleistocene faunal assemblage from the central Rocky Mountains, Colorado.What is the intellectual merit of the proposed research?The investigators propose to determine the range of animal use of the environment in a novel way. They plan to assess habitat use through time in a series of fossiliferous localities from three Rocky Mountain localities. In the absence of such analyses, the spatial component of sampling bias cannot be accounted for in most studies of either modern or paleontologic assemblages. This analysis will determine to what extent strontium isotopes can be used as a tool for assessing the ecological fidelity of the fossil record.What are the broader impacts resulting from the proposed research?The methods and results from this study will be of interest to paleontologists interested in reconstruction of past communities and to ecologists intent on understanding the spatial scale of ecosystem functioning. This research also has relevance to other specialists such as evolutionists, conservationists, geologists, and behaviorists. Through the synthesis of several fields and integration of diverse field, analytical and statistical methods, Hadly and Paytan emphasize the interdisciplinary training of graduate and undergraduate students.