The effect of food hardness on feeding behaviour in frugivorous bats (Phyllostomidae): an experimental study

Most New World leaf-nosed bats (Phyllostomidae) are frugivores. Many of these species are sympatric and mechanisms of resource partitioning including vertical stratification and divergent foraging strategies have been described. This study investigates a previously unexplored but potentially significant factor in resource partitioning: the relationship between feeding behaviour and fruit hardness. Data summarizing ingestive and fruit processing behaviours were collected during feeding experiments from five sympatric frugivorous phyllostomid species: Artibeus jamaicensis, Dermanura phaeotis, Sturnira lilium, Carollia perspicillata, and Glossophaga soricina. Individuals were the subjects of feeding experiments that consisted of eating hard and soft fruits of similar size, shape, and mass. Variables analysed from videotapes of the experiments describe how fruits are placed in the mouth during ingestion, the frequency of head movements during biting, the number of bites used to remove a piece of fruit, and the number of chews used to process each mouthful of fruit. Results of chi-square, log-linear, R x C, and Kruskal-Wallis tests demonstrate that feeding behaviours vary significantly with fruit hardness both within and between species. Artibeus, Dermanura, and Sturnira are behaviourally specialized for feeding on relatively hard fruits. However, Carollia, and probably Glossophaga, lack these behavioural specializations. Both mechanical and ecological implications of intra- and interspecific behavioural variation are discussed. Differences in fruit handling behaviour are also used to make explicit predictions regarding interspecific variation in masticatory morphology. This study demonstrates that the relationship between fruit hardness and feeding behaviour may be an integral part of frugivore ecology. Overall, resource partitioning among phyllostomid frugivores is a result of complex interactions among and between bats and their food plants. Controlled experimental studies such as this one provide a crucial means of dissecting these complex interactions and gaining insight into the basis of frugivore diversity.