| The ecology of strangler figs (hemiepiphytic Ficus spp., subgenus Urostigma) was studied in lowland mixed dipterocarp forest in Gunung Palung National Park, West Kalimantan, Indonesian Borneo, to address the limitations on fig abundance and the maintenance of Ficus species diversity in rain forests. Forty-five dipterocarps climbed with ropes were used to study germination and seedling establishment of Ficus stupenda in 336 natural sites and in planter boxes placed in the canopy and monitored for 12 months. The presence of substrate with good moisture retention (soil, rotting wood, moss) was the most important factor for germination. Overall establishment success after 12 months was only 1.3% of 6720 seeds planted, and only three seedlings (0.04%) showed vigorous growth. Knotholes were the best establishment sites, but were rare, with less than one per tree. High growth rates in canopy planter boxes compared with natural sites showed that water stress was the critical factor for seedling growth in the canopy. Water can thus be severely limiting for canopy plants, even in a very wet climate. Seed harvesting by a newly discovered species of arboreal Pheidole ant, present in 24% of canopy trees surveyed, significantly reduced fig germination and establishment, showing that canopy ants could have an important effect on hemiepiphytic fig reproduction. Seed shadows measured around four F. stupenda and three F. subtecta trees fit distributions suggesting that vertebrate dispersal produces higher seed rain at greater distances than wind dispersal. Nonetheless, the probability of seeds hitting safe sites in the canopy was calculated to be very low. Several factors were thus identified that help explain the rarity of strangler figs in contrast to the number of available host trees in the rain forest. In a survey of 135 hemiepiphytic fig individuals representing five species, highly significant differences were found among species in establishment site heights on hosts, canopy levels of fig crowns, and host taxa. Severe limitations on recruitment success for fig seedlings suggest that the observed specializations by different species are unlikely to be due to competition since numerous fig species appear to coexist with little interaction in the rain forest. |
