Mapping the Origin of Terrestrial Faunal Assemblages Using Strontium Isotopes

摘要化石记录被用来提高我们对人口对气候变化的反应的理解，并作为预测未来生态系统反应的指南。然而，迄今为止，对化石记录的解释都是基于两个未经检验的假设。首先，在化石记录中看到的响应的空间尺度，特别是在陆地环境中，是很好的理解，其次，随着时间的推移，群落的变化代表了当地人口的变化，而不是采样区域的变化。PIs Hadly和Paytan建议通过分析来自黄石国家公园的丰富骨骼化石序列的锶同位素组成来测试这些假设。黄石公园的序列跨越了过去的3000年，并通过化石遗址附近的全面现代收集而得到增强。由于锶同位素不是通过生物过程分馏出来的，基岩和上覆风化层的锶含量、从土壤中吸收锶的植被和消耗植被的动物将密切相关。采样地点分布在一个不均匀的地质景观中，每个地点的基岩具有明显不同的87Sr/86Sr同位素特征。如果化石地点代表当地的集合，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，如果这些地点的收集半径很大，并结合了地区平均锶值，他们预计的值与当地基岩大不相同（可能彼此更相似）。初步数据表明，这些化石组合各自具有不同的Sr同位素组成，代表了当地的基岩。pi将决定是否有可能排除收集区域随时间的变化，并在统计上限制对给定地点的生态、进化和古气候解释的应用范围。此外，pi建议通过调查来自科罗拉多州落基山脉中部更新世动物组合的样本来检验他们方法的普遍性。拟议研究的智力价值是什么？研究人员建议用一种新颖的方法来确定动物利用环境的范围。他们计划在三个落基山脉地区的一系列化石地点评估栖息地的使用情况。在缺乏这种分析的情况下，在大多数现代或古生物组合的研究中，采样偏差的空间成分都不能被解释。这项分析将决定锶同位素在多大程度上可以用作评估化石记录的生态保真度的工具。拟议的研究有何更广泛的影响？这项研究的方法和结果将对对过去群落重建感兴趣的古生物学家和对理解生态系统功能的空间尺度感兴趣的生态学家感兴趣。这项研究也与其他专家有关，如进化论者、自然资源保护主义者、地质学家和行为主义者。Hadly和Paytan通过多个领域的综合和多种领域、分析和统计方法的整合，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.