20世纪南极菲尔德斯半岛毛皮海豹食谱比例变化的同位素混合模型比较分析

稳定同位素比值分析已成功用于示踪动物的食物来源研究,近年来已发展了多个同位素混合模型用于计算混合物中多来源物质的组成比例。本文以过去百年来南极菲尔德斯半岛南极毛皮海豹(Arctocephalus gazella)毛发的C、N同位素数据为基础,运用同位素混合模型中的欧几里得距离法、线性模型和贝叶斯模型进行计算、分析和比较,得到毛皮海豹食谱中南极磷虾(Euphausia superb)、南极电灯鱼(Electrona antarctica)和尼氏裸灯鱼(Gymnoscopelus nicholsi)所占比例随时间的变化趋势。各模型计算得出的结果可分为两组,分别是欧几里得距离法公式(1)和(2)的结果,表现为近百年来毛皮海豹食谱中Euphausia superb比例与其毛发稳定N同位素比值呈同步上升的趋势;第二组为欧几里得距离法公式(3)、线性模型和贝叶斯模型的结果,Euphausia superb比例与毛皮海豹毛稳定N同位素比值呈反相关关系。综合对比研究区域气候、海冰环境变化背景和已有的南极磷虾种群密度调查资料分析,第二组模型结果与实际情况较为相符,可用于讨论食物比例的时间变化趋势。近百年来,菲尔德斯半岛毛皮海豹食谱中Euphausia superb的比例显著下降,很可能是由于区域气候快速变暖和海冰的消退造成的。本文的计算结果指示西南极半岛气候变暖已显著影响到区域海洋食物链变化。

Stable isotope mixing models in analyses of dietary changes of Antarctic fur seal in Fildes Peninsula,Antarctica over the 20th century

Stable isotope analysis has been used powerfully in tracing animal dietary sources. In the recent decades, many mixing models have been exploited to calculate source proportional contributions to a mixture based on stable isotope analyses. Here we present a case study by using Euclidean, Linear and Bayesian stable isotope mixing models to calculate proportion of Euphausia superba, Electrona antarctica and Gymnoscopelus nicholsi in Antarctic fur seal (Arctocephalus gazelle) diets over the 20th century. The Euphausia superba proportions in fur seal diets obtained from formula (1) and (2) of Euclidean method show a rising trend over the 20th century, similar to those δ15N of fur seal hairs. While the results given by formula (3) of Euclidean, Linear and Bayesian models show a declining trend, which are in accord with those recent changes in regional climate, sea ice extent and the observational Euphausia superba density. The results here can be used to study the biological response to climate change in a long time period. The calculated decline of krill proportion in seal diets over the past century indicates a decreasing trend of Euphausia superba population which is very likely due to the recent rapid regional warming and sea ice loss. Our results suggest that recent warming in the West Antarctic Peninsula has had an obvious impact on the regional marine food chains.