Diet selection of white-tailed deer supports the nutrient balance hypothesis.

Herbivores must navigate a heterogeneous matrix of nutrients in plant communities to meet physiological requirements. Given that the only difference between an essential nutrient and a toxin is the concentration in the herbivores diet, heterogeneity of nutrient concentrations in plant communities likely force wild herbivores to balance intake of abundant nutrients that may reach toxic levels with the need to meet nutritional demands of rare nutrients (i.e., nutrient balance hypothesis). While this hypothesis has been demonstrated in controlled studies with captive herbivores, experiments testing the nutrient balance hypothesis with wild herbivores are rare. We designed a cafeteria-style experiment to measure use of forages with differing nutritional compositions by wild white-tailed deer (Odocoileus virginianus) to test the nutrient balance hypothesis. We predicted deer diet selection would be explained by attraction to some nutrients and avoidance of others. Deer selected forages with low sulfur concentrations, a nutrient that commonly reaches toxic levels in herbivores. However, deer secondarily selected forages with greater digestibility and crude protein. Thus, our data indicate that the nutrient balance hypothesis may explain diet selection in wild herbivores where they avoid reaching toxicity of abundant nutrients while secondarily maximizing intake of limiting nutrients.