Hebert Craig E, Weseloh D V Chip, Gauthier Lewis T, Arts Michael T, Letcher Robert J
Environment Canada, Wildlife and Landscape Science Directorate, National Wildlife Research Centre, Ottawa, ON, Canada.
Oecologia. 2009 May;160(1):15-23. doi: 10.1007/s00442-009-1285-1. Epub 2009 Feb 14.
Food web structure regulates the pathways and flow rates of energy, nutrients, and contaminants to top predators. Ecologically and physiologically meaningful biochemical tracers provide a means to characterize and quantify these transfers within food webs. In this study, changes in the ratios of stable N isotopes (e.g., delta(15)N), fatty acids (FA), and persistent contaminants were used to trace food web pathways utilized by herring gulls (Larus argentatus) breeding along the shores of the St Lawrence River, Canada. Egg delta(15)N values varied significantly among years and were used as an indicator of gull trophic position. Temporal trends in egg delta(15)N values were related to egg FA profiles. In years when egg delta(15)N values were greater, egg FA patterns reflected the consumption of more aquatic prey. Egg delta(15)N values were also correlated with annual estimates of prey fish abundance. These results indicated that temporal changes in aquatic prey availability were reflected in the gull diet (as inferred from ecological tracer profiles in gull eggs). Analysis of individual eggs within years confirmed that birds consuming more aquatic prey occupied higher trophic positions. Furthermore, increases in trophic position were associated with increased concentrations of most persistent organic contaminants in eggs. However, levels of highly brominated polybrominated diphenyl ether congeners, e.g, 2,2',3,3',4,4',5,5',6,6'-decabromoDE (BDE-209), showed a negative relationship with trophic position. These contrasting findings reflected differences among contaminant groups/homologs in terms of their predominant routes of transfer, i.e., aquatic versus terrestrial food webs. High trophic level omnivores, e.g., herring gulls, are common in food webs. By characterizing ecological tracer profiles in such species we can better understand spatial, temporal, and individual differences in pathways of contaminant, energy, and nutrient flow.
食物网结构调节着能量、营养物质和污染物流向顶级捕食者的途径和速率。具有生态和生理意义的生化示踪剂提供了一种手段来表征和量化食物网内的这些转移。在本研究中，稳定氮同位素（如δ(15)N）、脂肪酸（FA）和持久性污染物的比例变化被用于追踪在加拿大圣劳伦斯河岸繁殖的银鸥（Larus argentatus）所利用的食物网途径。卵的δ(15)N值在不同年份间有显著差异，并被用作鸥类营养级的指标。卵δ(15)N值的时间趋势与卵的脂肪酸谱相关。在卵δ(15)N值较高的年份，卵的脂肪酸模式反映出更多水生猎物的消耗。卵δ(15)N值也与被捕食鱼类丰度的年度估计值相关。这些结果表明，水生猎物可利用性的时间变化反映在鸥类的饮食中（如从鸥卵中的生态示踪剂谱推断）。对同一年份内单个卵的分析证实，消耗更多水生猎物的鸟类占据更高的营养级。此外，营养级的升高与卵中大多数持久性有机污染物浓度的增加有关。然而，高溴化多溴二苯醚同系物的水平，如2,2',3,3',4,4',5,5',6,6'-十溴二苯醚（BDE - 209），与营养级呈负相关。这些对比结果反映了污染物组/同系物在其主要转移途径方面的差异，即水生食物网与陆地食物网。高营养级杂食动物，如银鸥，在食物网中很常见。通过表征此类物种的生态示踪剂谱，我们可以更好地理解污染物、能量和营养物质流动途径的空间、时间和个体差异。
