Although pollen is included in the diet of vertebrates and invertebrates, and extraction efficiency of its contents has been estimated for several flower visitors, the relationship between feeding habits and pollen digestion efficiency has not been carefully studied. We compared the efficiency with which four species of New World bats with different feeding habits extracted the contents of different types of pollen, and we tested the hypothesis that flower-visiting bats have higher extraction efficiencies than fruit-eating bats. We gave doses of different types of pollen to two nectarivorous (Anoura geoffroyi and Leptonycteris curasoae) and two frugivorous (Artibeus jamaicensis and Sturnira lilium) bats and collected their feces at regular intervals. We used pollen from three species of flowers that are associated with bat visitation: Pseudobombax ellipticum, Hylocereus undatus, and an unidentified species of night-blooming, columnar cactus. In addition to estimating the percentage of empty pollen grains in the feces, we determined digesta time distributions in the gastrointestinal tract and interpreted them using chemical reactor theory. Extraction efficiency was higher in bats that regularly include pollen in their diet. This pattern was not explained by differences in the rate with which the bats processed pollen, or by the time that pollen was retained in the stomach, where little degradation of pollen grains occurs. Within species, however, the percentage of empty grains increased asymptotically with time in the gastrointestinal tract. In general, the digestive system of the bats seemed to process pollen grains as a continuous stirred-tank reactor (CSTR) connected to a plug-flow reactor (PFR), with longitudinal mixing in the PFR: the food was retained for a relatively short period in the stomach and then was moved through the intestine, where it was mixed longitudinally. Artibeus jamaicensis was an exception to this pattern in the way its digestive system processed H. undatus pollen; in this case, its gastrointestinal tract apparently functioned as a PFR with a considerable amount of longitudinal mixing. We hypothesize that differences among bats in extraction efficiency of pollen contents may be partly explained by differences in the intestinal activity of the enzymes responsible for pollen grain degradation.
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