Benstead Jonathan P, March James G, Fry Brian, Ewel Katherine C, Pringle Catherine M
Institute of Ecology, University of Georgia, Athens 30602, USA.
Ecology. 2006 Feb;87(2):326-33. doi: 10.1890/05-0721.
We sampled consumers and organic matter sources (mangrove litter, freshwater swamp-forest litter, seagrasses, seagrass epiphytes, and marine particulate organic matter [MPOM]) from four estuaries on Kosrae, Federated States of Micronesia for stable isotope (sigma13C and sigma34S) analysis. Unique mixing solutions cannot be calculated in a dual-isotope, five-endmember scenario, so we tested IsoSource, a recently developed statistical procedure that calculates ranges in source contributions (i.e., minimum and maximum possible). Relatively high minimum contributions indicate significant sources, while low maxima indicate otherwise. Litter from the two forest types was isotopically distinguishable but had low average minimum contributions (0-8% for mangrove litter and 0% for swamp-forest litter among estuaries). Minimum contribution of MPOM was also low, averaging 0-13% among estuaries. Instead, local marine sources dominated contributions to consumers. Minimum contributions of seagrasses averaged 8-47% among estuaries (range 0-88% among species). Minimum contributions of seagrass epiphytes averaged 5-27% among estuaries (range 0-69% among species). IsoSource enabled inclusion of five organic matter sources in our dual-isotope analysis, ranking trophic importance as follows: seagrasses > seagrass epiphytes > MPOM > mangrove forest > freshwater swamp-forest. IsoSource is thus a useful step toward understanding which of multiple organic matter sources support food webs; more detailed work is necessary to identify unique solutions.
我们从密克罗尼西亚联邦科斯雷岛的四个河口采集了消费者以及有机物质来源样本（红树林凋落物、淡水沼泽森林凋落物、海草、海草附生植物和海洋颗粒有机物质[MPOM]），用于稳定同位素（δ¹³C和δ³⁴S）分析。在双同位素、五端元的情况下无法计算出唯一的混合解，因此我们测试了IsoSource，这是一种最近开发的统计程序，用于计算来源贡献范围（即最小和最大可能值）。相对较高的最小贡献表明是重要来源，而较低的最大值则表明并非如此。两种森林类型的凋落物在同位素上是可区分的，但平均最小贡献较低（河口间红树林凋落物为0 - 8%，沼泽森林凋落物为0%）。MPOM的最小贡献也较低，河口间平均为0 - 13%。相反，当地海洋来源对消费者的贡献占主导。河口间海草的最小贡献平均为8 - 47%（物种间范围为0 - 88%）。河口间海草附生植物的最小贡献平均为5 - 27%（物种间范围为0 - 69%）。IsoSource使我们能够在双同位素分析中纳入五种有机物质来源，营养重要性排序如下：海草>海草附生植物>MPOM>红树林>淡水沼泽森林。因此，IsoSource是朝着了解多种有机物质来源中哪些支持食物网迈出的有用一步；还需要更详细的工作来确定唯一解。
