A physiological perspective on nectar-feeding adaptation in phyllostomid bats.

Nectar-feeding animals increase their food intake when nectar sugar concentration decreases. However, some species present physiological constraints that limit their energy intake when nectar is diluted. We hypothesized that gut capacities of bats affect the ability of these animals to acquire and store energy, modifying how they use food resources in the field. We measured the food intake and changes in body mass of the members of an assemblage of nectar-feeding bats (Choeronycteris mexicana, Leptonycteris yerbabuenae, and Glossophaga soricina) feeding on sucrose solutions of different concentrations (146, 292, 438, 584, 730, 876, and 1,022 mmol L(-1)). The three bat species presented differences in their food intake and their capacity to store energy. While C. mexicana was able to maintain a constant energy intake at all concentrations tested, G. soricina and L. yerbabuenae decreased their sugar/energy intake at the lowest sugar concentrations. Choeronycteris mexicana also increased body mass independent of sugar concentration, while G. soricina and L. yerbabuenae did not. On the basis of our results, we generated a model relating gut capacities and the use of food resources in the field. Our model's predictions and field data support the idea that digestive traits affect the way these animals use the food resources present in their environment.