Anonymous faecal sampling and NIRS studies of diet quality: problem or opportunity?

Investigating the drivers of diet quality is a key issue in wildlife ecology and conservation. Faecal near infrared reflectance spectroscopy (f-NIRS) is widely used to study dietary quality since it allows for noninvasive, rapid and low-cost analysis of nutrients. Samples for f-NIRS can be collected and analyzed with or without knowledge of animal identities. While anonymous sampling allows to reduce the costs of individual identification, as it neither requires physical captures nor DNA genotyping, it neglects the potential effects of individual variation in dietary quality and may suffer severe issues of pseudoreplication. I investigated the relationship between crude protein and ecological predictors at different time periods to assess the level of individual heterogeneity in dietary quality of 22 marked chamois Rupicapra rupicapra monitored over two years. Models with and without individual grouping effect were fitted to simulate identifiable and anonymous faecal sampling, and model...