Research School of Biology, Australian National University, Canberra, Australia.
Oecologia. 2013 Sep;173(1):203-12. doi: 10.1007/s00442-013-2616-9. Epub 2013 Feb 27.
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.
估算食草动物饮食的营养价值很困难，因为这需要知道动物吃什么、每种成分的相对质量以及这些成分与动物生理之间的相互作用。目前的方法繁琐，并且依赖于许多难以评估的假设。我们描述了一种从粪便中直接估算相对饮食质量的新方法，该方法避免了其他方法固有的问题。我们将这种方法与近红外反射光谱（NIRS）相结合，分析了许多样本，从而为生态研究提供了一种非常有价值的技术。该方法源于食用无单宁饮食的食草动物粪便中饮食氮和粪便氮浓度之间的相关性，但在摄入大量单宁的食草动物（如 browsers）中，这种关系较弱，因为单宁与蛋白质形成复合物。这些复合物会降低氮的可利用性，并可能增加粪便氮浓度。使用单宁结合化合物聚乙二醇，我们表明，单宁结合氮是野生普通帚尾袋貂（Trichosurus vulpecula）粪便氮的一个重要且可变的部分。我们开发了一种测量粪便可利用氮的技术，并发现它可以预测澳大利亚北部帚尾袋貂的繁殖成功率。粪便可利用氮与 NIRS 相结合，为估算许多生态系统中食草动物的相对营养值提供了强大的工具。它是一种比其他常用的单一营养物测量方法（如粪便氮和与观察到的觅食行为配对的叶片分析）更好的饮食质量指标。
