Compound information for analyzed fecal steroids.

Molecular biomarkers preserved in lake sediments are increasingly used to develop records of past organism occurrence. When linked with traditional paleoecological methods, analysis of molecular biomarkers can yield new insights into the roles of herbivores and other animals in long-term ecosystem dynamics. We sought to determine whether fecal steroids in lake sediments could be used to reconstruct past ungulate use and dominant taxa in a small catchment in northern Yellowstone National Park. To do so, we characterized the fecal steroid profiles of a selection of North American ungulates historically present in the Yellowstone region (bison, elk, moose, mule deer, and pronghorn) and compared them with those of sediments from a small lake in the Yellowstone Northern Range. Analysis of a set of fecal steroids from herbivore dung (Δ5-sterols, 5α-stanols, 5β-stanols, epi5β-stanols, stanones, and bile acids) differentiated moose, pronghorn, and mule deer, whereas bison and elk were partially differentiated. Our results show that bison and/or elk were the primary ungulates in the watershed over the past c. 2300 years. Fecal steroid influxes reached historically unprecedented levels during the early and middle 20th century, possibly indicating high local use by ungulates. Comparison of fecal steroid influxes with pollen and diatom data suggests that elevated ungulate presence may have contributed to decreased forage taxa (Poaceae, Artemisia, and Salix), relative to long-term averages, and possibly increased lake production. Our results reflect past change within a single watershed, and extending this approach to a network of sites could provide much-needed information on past herbivore communities, use, and environmental influences in Yellowstone National Park and elsewhere.保存在湖泊沉积物（lake sediments）中的分子生物标志物（molecular biomarkers）正日益被用于重建过去生物的出现记录。当与传统古生态学方法（paleoecological methods）相结合时，分子生物标志物分析能够为草食动物（herbivores）及其他动物在长期生态系统动态中的作用提供新的见解。本研究旨在探究湖泊沉积物中的粪便类固醇（fecal steroids）是否可用于重建黄石国家公园（Yellowstone National Park）北部某小型集水区（catchment）内过去有蹄类动物（ungulate）的活动情况及优势类群。为此，我们对黄石地区历史上存在的多种北美有蹄类动物——美洲野牛（bison）、马鹿（elk）、驼鹿（moose）、骡鹿（mule deer）及叉角羚（pronghorn）——的粪便类固醇谱图进行了表征，并将其与黄石北部区域某小型湖泊的沉积物谱图进行了比对。通过对草食动物粪便中一组涵盖Δ5-甾醇（Δ5-sterols）、5α-甾烷醇（5α-stanols）、5β-甾烷醇（5β-stanols）、表5β-甾烷醇（epi5β-stanols）、甾酮类（stanones）及胆汁酸（bile acids）的粪便类固醇进行分析，可有效区分驼鹿、叉角羚与骡鹿，而美洲野牛与马鹿则可实现部分区分。研究结果显示，在过去约2300年中，美洲野牛和/或马鹿是该流域内的主要有蹄类动物。20世纪早中期，粪便类固醇输入通量达到了历史前所未有的水平，这可能表明当时该区域有蹄类动物活动强度较高。将粪便类固醇输入通量与花粉（pollen）、硅藻（diatom）数据进行比对后发现，相较于长期平均水平，有蹄类动物活动增强可能导致了可采食植物类群（禾本科（Poaceae）、蒿属（Artemisia）及柳属（Salix））占比下降，同时可能提升了湖泊生产力。本研究结果仅反映了单个流域内的过去环境变化，若将该方法推广至多站点网络，则可为黄石国家公园乃至全球其他区域的过去草食动物群落、活动情况及环境影响提供亟需的科研数据。