Fecal Indices to Dietary Quality: A Critique

Abstract

Fecal nitrogen (N) concentration has been widely advocated as a predictor of diet quality in herbivores. Despite its apparent utility, the technique has fundamental biological and statistical limitations. Regression relationships based on variation in fecal and diet N among seasons may be highly misleading when used to compare diets of populations within seasons. The slopes of those regressions depend on many environmental and dietary influences that vary with time and location. Inter-animal variability in fecal N reduces the precision of diet quality predictions, and the ubiquitous presence of tannins in dicotyledonous diets limits their accuracy. I conclude that the fecal N technique does not currently offer reliable, quantitative predictions of diet quality in herbivores.