ECOLOGICAL AND BEHAVIORAL CONSEQUENCES OF DIGESTION IN FRUGIVOROUS ANIMALS

The postingestional effect of seed size and mass and nutrient composit ion on fruit profitability are reviewed. It is emphasized that profita bility results from the interaction between fruit characteristics and the physiological and morphological traits of frugivores. The processe s by which frugivores regurgitate or defecate seeds and the differenti al processing of the nutrient rich pulp and ballast in fruit are stron gly dependent on the interaction between frugivore gut morphology and seed size. Euphonias that lack a functional gizzard defecate seeds, wh ereas tanagers that have a delete a functional gizzards regurgitate se eds. Some frugivores separate seeds from pulp and exocarp in the gizza rd. It is hypothesized that the gizzard plays an important role in det ermining the postingestional fate of different pulp components. Althou gh fruit nutrient content is often invoked as a determinant of frugivo re feeding choices, studies that rely on proximal nutrient analysis, h ave often failed to find clear nutrient composition-preference correla tions. It is argued that a partial reason for this failure is that pro ximal nutrient analysis ignores the complexities of fruit digestion. T he ecological and physiological correlates of lipid and sugar assimila tion are used to identify the limitations of traditional proximal nutr ient analyses in fruit-frugivore studies. We suggest that recognizing the intricacies of the digestive characteristics of frugivores may rev eal a much richer patterning in the interaction of frugivores with pla nts than has been previously hypothesized.