Focal vs. faecal: Seasonal variation in the diet of wild vervet monkeys from observational and DNA metabarcoding data

1. Assessing the diet of wild animals reveals valuable information about their ecology and trophic relationships that may help elucidate dynamic interactions in ecosystems and forecast responses to environmental changes. 2. Advances in molecular biology provide valuable research tools in this field. However, comparative empirical research is still required to highlight strengths and potential biases of different approaches. Therefore, this study compares environmental DNA and observational methods for the same study population and sampling duration. 3. We employed DNA metabarcoding assays targeting plant and arthropod diet items in 823 faecal samples collected over 12 months in a wild population of an omnivorous primate, the vervet monkey (Chlorocebus pygerythrus). DNA metabarcoding data were subsequently compared to direct observations. 4. We observed the same seasonal patterns of plant consumption with both methods, however, DNA metabarcoding showed considerably greater taxonomic coverage and resolution compared to observations, mostly due to the construction of a local plant DNA database. We found a strong effect of season on variation in plant consumption largely shaped by the dry and wet seasons. The seasonal effect on arthropod consumption was weaker but feeding on arthropods was more frequent in spring and summer, showing overall that vervets adapt their diet according to available resources. The DNA metabarcoding assay outperformed also direct observations of arthropod consumption in both taxonomic coverage and resolution. 5. Combining traditional techniques and DNA metabarcoding data can therefore not only provide enhanced assessments of complex diets or reveal trophic interactions to the benefit of wildlife conservationists and managers but also opens new perspectives for behavioural ecologists studying whether diet variation in social species is induced by environmental differences or might reflect selective foraging behaviours.

1. 评估野生动物的饮食构成，可揭示其生态学特征与营养关系的宝贵信息，有助于阐明生态系统内的动态交互过程，并预测物种对环境变化的响应。
2. 分子生物学技术的进步为该研究领域提供了极具价值的研究工具。然而，当前仍需开展对比性实证研究，以明确不同研究方法的优势与潜在偏倚。因此，本研究针对同一研究种群与采样周期，对比了环境DNA（environmental DNA）与观测法两种研究手段。
3. 本研究针对一个野生杂食性灵长类种群——长尾黑颚猴（Chlorocebus pygerythrus），在12个月的采样周期内收集了823份粪便样本（faecal sample），并采用靶向植物与节肢动物饮食组分的DNA metabarcoding（DNA元条形码技术）进行检测。随后将DNA metabarcoding数据与直接观测结果进行对比分析。
4. 两种方法均观测到了植物取食的季节性模式，但DNA metabarcoding技术展现出远高于观测法的分类学覆盖度与分辨率，这主要得益于本地植物DNA数据库的构建。研究发现，季节对植物取食变异存在显著影响，该变异主要由干湿季差异塑造；而季节对节肢动物取食的影响相对较弱，但春季与夏季的节肢动物取食频率更高。整体而言，长尾黑颚猴会根据可获取的资源调整其饮食结构。此外，在节肢动物取食的分类学覆盖度与分辨率方面，DNA metabarcoding技术同样优于直接观测法。
5. 因此，将传统观测技术与DNA metabarcoding数据相结合，不仅能够提升复杂饮食构成的评估精度，揭示更多营养交互关系，进而为野生动物保护者与管理者提供助力，同时也为行为生态学家开展相关研究开辟了新视角——这类研究可探讨社会物种的饮食变异究竟由环境差异驱动，还是反映了选择性觅食行为。