Use of near-infrared reflectance spectroscopy to quantify diet mixing in a generalist marine herbivore
The diet of individual animals in the field is governed by behavioural preference as well as factors intrinsic and extrinsic to the organism that may constrain their ability to obtain preferred foods. Accurate measurements of individual diets are essential to understanding how consumers can impact communities, but can be difficult to obtain. We aim to determine whether near-infrared reflectance spectroscopy (NIRS) can be used to quantify the degree of diet mixing in the diet of a generalist herbivore, the marine gastropod Lunella torquatus. NIRS successfully classified five algal diets and could quantify the proportions of these species in two-species combinations. We then assessed whether NIRS could predict dietary composition post-digestion by contrasting faecal material from single-species and mixed diets. Partial least squares methods were used to develop prediction models that effectively discriminated among species and, for most species, effectively predicted the proportion of a given species in all possible two-species mixtures. NIRS thus has the potential to provide a non-invasive method for assessing the realised diets of free-living herbivores.