The value of figs to a hind-gut fermenting frugivore: a nutritional analysis

Abstract

The fleshy wall of figs is an important food item for a wide range of frugivore animals. However, the nutritional significance of figs as a genus is poorly understood and somewhat puzzling, since there is considerable variation among species in chemical content. This study examined nutritional features of nine species of Ugandan figs, from Kibale Forest, eaten by chimpanzees ( Pan troglodytes) and many other frugivores. Fig samples were chemically analyzed for their percentages of lipid, crude protein (CP), available protein, water-soluble carbohydrates (WSC), pectin, total cell wall, hemicellulose, cellulose, lignin, cutin, tannins, dry matter and total ash. Complex carbohydrates ( cxCHO) were calculated by difference. The pulp or flesh of the figs was analyzed separately from the seed fraction. None of the assayed nutrients alone explain why figs are eaten by so many of the frugivores in Kibale Forest. Furthermore, standard calculations suggested that figs have rather low values of metabolizable energy (ME). However ME may be misunderstood when calculated by the orthodox method, because it does not aknowledge nutritional components available to frugivores capable of fore- or hind-gut fermentation. As a result of including pectin, hemicellulose and cellulose as potential energy sources through fermentation, we suggest that total ME for a chimpanzee is some 50% higher (2.78 kcal g −1 compared to 1.91 kcal g −1) than estimated purely on the basis of cxCHO, WSC, CP and lipid. When calculated in this way, the digestibility/fermentability of soluble and insoluble fiber components may explain the attractiveness of figs to many frugivores.