The influence of plant defensive chemicals, diet composition, and winter severity on the nutritional condition of a free-ranging, generalist herbivore

When consuming plants, herbivores must deal with both low nutritional quality from cell wall constituents and potentially toxic plant secondary metabolites, which are often inversely related. Herbivores that consume a highly nutritious, but chemically defended plant, may consume high levels of toxins that require energy for detoxification. Alternatively, herbivores may avoid consuming high levels of toxins by consuming a diverse diet that may be lower in overall nutritional quality. In this study, we assessed the relationship among nutritional restriction, detoxification and diet diversity in a free-ranging wild herbivore. We collected urine deposited in the snow (hereafter, snow-urine) and feces by free-ranging moose Alces americanus, a generalist browser, during winter. We used the ratio of urinary urea nitrogen to creatinine (UN:C), measured in snow-urine samples, as an indicator of nutritional restriction, and the ratio of glucuronic acid to creatinine (GA:C), as an indicator of inv...