Otterly delicious: Spatiotemporal variation in the diet of a recovering population of Eurasian otters (Lutra lutra) revealed through DNA metabarcoding and morphological analysis of prey remains

Eurasian otters are apex predators of freshwater ecosystems and a recovering species across much of their European range; investigating the dietary variation of this predator over time and space therefore provides opportunities to identify changes in freshwater trophic interactions and factors influencing the conservation of otter populations. Here we sampled faeces from 300 dead otters across England and Wales between 2007 and 2016, conducting both morphological analysis of prey remains and dietary DNA metabarcoding. Comparison of these methods showed that greater taxonomic resolution and breadth could be achieved using DNA metabarcoding but combining data from both methodologies gave the most comprehensive dietary description. All otter demographics exploited a broad range of taxa and variation likely reflected changes in prey distributions and availability across the landscape. This study provides novel insights into the trophic generalism and adaptability of otters across Britain, w..., Sample and data collection Samples and associated metadata were acquired from 300 otters collected between 2007 and 2016, obtained from the Cardiff University Otter Project, a national monitoring programme for dead otters sampled from across Great Britain (https://www.cardiff.ac.uk/otter-project). Most otters collected were killed by road traffic accidents, with a minority dying through drowning, being shot, starvation, or disease. Information on date (year and month) and location (as grid reference) of carcass collection were recorded at the site of collection. Grid references were used to plot data for spatial analysis. Detailed post-mortems were performed for each carcass during which biotic data were obtained (e.g., sex and size of individual). Faecal samples were collected from the rectum during post-mortem examination, wrapped in foil and stored at -20 °C. Following post-mortems, scaled mass index (SMI) was calculated for each individual otter using the following equation (Peig an...,欧亚水獭（Eurasian otter）是淡水生态系统中的顶级捕食者，在其欧洲分布范围的大部分区域正处于种群恢复阶段；因此，探究该捕食者在时空维度上的食性变化，有助于识别淡水营养级相互作用的改变以及影响水獭种群保护的相关因素。本研究于2007年至2016年间，在英格兰与威尔士全境采集了300具死亡水獭的粪便样本，同时开展了猎物残骸的形态学分析与饮食DNA宏条形码（dietary DNA metabarcoding）检测。对比两种方法的结果显示，DNA宏条形码技术可获得更高的分类学分辨率与更宽的分类覆盖度，但结合两种方法的数据能够得到最全面的食性描述。所有年龄与性别类群的水獭均取食广泛的猎物类群，其食性差异大概率反映了猎物在景观中的分布与可获得性变化。本研究为英国境内水獭的营养泛化性与适应性提供了全新的认知，…… 样本与数据采集： 样本及相关元数据来自2007至2016年间收集的300具水獭样本，这些样本由加的夫大学水獭项目（Cardiff University Otter Project）提供——该项目是针对大不列颠全境死亡水獭的全国性监测计划（https://www.cardiff.ac.uk/otter-project）。本次采集的水獭大多死于道路交通事故，少数个体则因溺水、枪击、饥饿或疾病死亡。样本采集时记录了尸体的采集日期（年与月）与位置（网格坐标），网格坐标用于绘制数据以开展空间分析。对每具尸体均进行了详细的尸检，获取了个体的生物信息（如性别与体型）。粪便样本在尸检过程中从直肠采集，用铝箔包裹后保存于-20℃环境中。 尸检完成后，采用如下公式计算每只水獭的标准化体重指数（scaled mass index, SMI）（Peig an……）