Estimating the nutritional value of a herbivore's diet is difficult because it requires knowing what the animal eats, the relative quality of each component and how these components interact in relation to animal physiology. Current methods are cumbersome and rely on many assumptions that are hard to evaluate. We describe a new method for estimating relative diet quality directly from faeces that avoids the problems inherent in other methods. We combine this method with near infrared reflectance spectroscopy (NIRS) to analyse many samples and thus provide a technique with immense value in ecological studies. The method stems from the correlation between the concentrations of dietary and faecal nitrogen in herbivores eating a tannin-free diet, but a weaker relationship in browsers that ingest substantial amounts of tannins, which form complexes with proteins. These complexes reduce the availability of nitrogen and may increase faecal nitrogen concentrations. Using the tannin-binding compound, polyethylene glycol, we showed that tannin-bound nitrogen is a significant and variable part of faecal nitrogen in wild common brushtail possums (Trichosurus vulpecula). We developed a technique to measure faecal available nitrogen and found that it predicted the reproductive success of female brushtail possums in northern Australia. Faecal available nitrogen combined with NIRS provides a powerful tool for estimating the relative nutritional value of the diets of browsing herbivores in many ecological systems. It is a better indicator of diet quality than other commonly used single-nutrient measures such as faecal nitrogen and foliage analysis paired with observed feeding behaviour.

Item Type:	Refereed Article
Keywords:	herbivory; plant defenses; plant secondary metabolites;nutrition;tannins;available nitrogen;PEG browser
Research Division:	Biological Sciences
Research Group:	Ecology
Research Field:	Terrestrial ecology
Objective Division:	Animal Production and Animal Primary Products
Objective Group:	Fisheries - wild caught
Objective Field:	Fisheries - wild caught not elsewhere classified
UTAS Author:	Johnson, CN (Professor Christopher Johnson)
ID Code:	83768
Year Published:	2013
Web of Science® Times Cited:	16
Deposited By:	Zoology
Deposited On:	2013-03-21
Last Modified:	2022-08-18
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