KEYSTONE CHARACTERISTICS OF BIRD-DISPERSED FICUS IN A MALAYSIAN LOWLAND RAIN-FOREST

(1) The fruiting of 307 Ficus trees in 74 ha of lowland forest at Kuala Lompat, Malaysia, was monitored monthly for 3 years. (2) The guild of twenty-nine species of bird-dispersed Ficus exhibited asynchronous fruiting phenology, with no recurrent annual pattern. Fig crops were available in all 36 months of the study, but whilst medium-sized and small-sized figs were always available, crops of large-fruited (mean fig diameter of > 20 mm) bird-dispersed Ficus were scarce, with only around sixteen fruiting events year-1 km-2 of forest. (3) Seven Ficus species exhibited fruiting patterns which suggested some seasonality, with significantly more fruitings than expected in the period February-April. This period is before the usual major annual community peak in fruiting, at a time when other fruit resources are relatively scarce. (4) Ficus forms a uniquely important group within the subset of plants with bird-eaten fruit because of their numerical abundance, intra-crown synchrony of fruit ripening, relatively short intervals between fruiting, large crop sizes and intra-population fruiting asynchrony. These characteristics, combined with their availability at times when other fruits are scarce, makes Ficus a most important keystone plant resource. (5) For frugivores to be dependent on figs in South-east Asia they need to be wide-ranging. Frugivorous birds with small home ranges may have to rely on keystone plants other than Ficus during some periods of fruit scarcity.