Differential Effect of Fruit Availability on Avian Frugivore Guilds in a Moist Deciduous Forest of India

Abstract

Frugivores provide a critical ecosystem service by dispersing seeds and therefore play a major role in the survival and maintenance of trees in tropical forests. Avian frugivores constitute one of the major guilds in tropical forests whose activities are significantly governed by the availability of fruits across space and time. In our current study we examined the effects of the spatial and temporal pattern of food availability on avian frugivores and various avian frugivore functional groups in particular. We found a differential effect of fruit density and number of tree species in fruiting on different functional groups of avian frugivores along both spatial and temporal scales. Total frugivore density was best explained by ‘number of tree species in fruiting’ at both special and temporal scale. The variation in large frugivore density was best explained both by ‘fruit density’ and ‘fruit density’ and ‘number of tree species in fruiting’ together. This pattern was observed at a spatial scale but not along temporal scale. Along temporal scale large frugivore density was best explained only by ‘number of tree species in fruiting’. The medium sized frugivore density was not significantly explained by either ‘fruit density’ or ‘number of tree species in fruiting’. The medium sized frugivores are dependent both on insects and fruits and variation in insect density may determine spatial and temporal variation in medium sized frugivore density. The mixed diet frugivore group with a smaller gape width is limited by the variety of fruit they consume and thus their population was significantly controlled by the number of fleshy fruited tree species in fruiting along spatial scale. We observed breeding synchronization during the time of fruiting peak and we suggest that this could be a strategy for effective seed dispersal. Our study indicated very strong dependability of the large frugivore (dependent only on fruit) population on fruit availability unlike the mixed diet frugivore guild (fruit as secondary diet).