NUTRITIONAL ECOLOGY AND DIGESTIVE RESPONSES OF AN OMNIVOROUS-INSECTIVOROUS RODENT (ABROTHRIX LONGIPILIS) FEEDING ON FUNGUS

Spore retention by the digestive tract of mycophagous rodents may affe ct the temporal and spatial dynamics of spore dispersal; rodents may a lso benefit from consuming a discrete resource rich in minerals and vi tamins. Some research suggests that hypogeous fungi are not a nutritio nally high-quality food item for small rodents, regardless of being hi ghly consumed by these small mammals. Fungi may be a valuable dietary item when higher-quality food is in low abundance. However, the extent to which fungi are incorporated into diet will ultimately depend on t he physiological capacities of organisms for digesting such a resource . Here we investigate digestibility of fungus compared with insects an d young foliage of plants, and we draw inferences about digestive cons traints in a forest-dwelling, mycophagous, habitat-generalist rodent ( Abrothrix longipilis) exploiting different diets. We show that the fru iting bodies of fungi are less digestible than young leaves of plants and insects. The intake of fungus, in grams of dry mass per day, did n ot differ from the intake of plants. However, the wet intake of fungus was 23.8 g wet mass . d(-1), while the amount of plants consumed was 7.1 g wet mass . d(-1) and insect intake was 10.7 g wet mass . d(-1). In spite of small mammals' increasing the wet weight of food eaten as the quality and digestibility of the diet decreases, they may be unabl e to process the required amount of fungus fast enough to maintain the ir energy or matter budget and minimize the feeding time. Finally, and based on the fact that many insects utilize fungi as oviposition site s, we hypothesize for A. longipilis that a quantity of insect larvae i ngested with fruiting bodies of fungi confers a nutritional benefit be yond that of the fungi alone.