Factors Influencing Leaf Choice by Howler Monkeys: A Test of Some Hypotheses of Food Selection by Generalist Herbivores

Abstract

Some theories on the foraging strategies of generalist herbivores suggest that the food choices of such animals are greatly influenced by the quality and antiquality components of potential foods. Many herbivores selectively feed on young rather than mature foliage. It has been hypothesized that young leaves are preferred because they have higher contents of protein and/or lower contents of toxic secondary compounds. These and several other hypotheses were tested with data from a long-term study of the feeding ecology of howler monkeys (Alouatta palliata), using a cost/benefit approach. Samples of young and mature leaves from the same species were analyzed for total protein, cell wall constituents, total phenolics, presence of condensed tannins, and total nonstructural carbohydrates. The results support the hypothesis that more than one factor determine howler leaf choices. The most important factors (relating to food content) appeared to be protein and fiber content, with perhaps some influence from secondary compounds. For howlers and other relatively small mammalian herbivores, the protein: fiber ratio may be a good predictor of leaf choices.