Reproduction of dipterocarps during low intensity masting events in a Bornean rain forest

Abstract

Question: The evolution of general flowering and mast fruiting of dipterocarps in tropical rain forest has been explained by different mechanisms. We studied whether the abundance of flowering conspecifics influences the recruitment success of tropical forest trees in Borneo. Location: Sepilok Forest Reserve, Sabah, Malaysia. Method: We examined the recruitment success of 17 species of Dipterocarpaceae in a 640–ha sample area over two flowering events in 2001–2002 using seed traps and quadrats. Seed predation experiments were used to investigate if post‐dispersal seed survival was density‐dependent. Results: We found a negative relationship between the percentage of flowers abscised per individual and the number of flowering conspecifics and a positive relationship between the percent of flowering trees that produced viable seeds and the number of flowering conspecifics. However, we found no evidence of decreasing pre‐ and post‐dispersal predation with increasing numbers of flowering conspecifics. High levels of flower abscission, and pre‐ and post‐dispersal seed mortality, resulted in near‐complete recruitment failure of most species, with only three species successfully recruiting in only one year. One of these, Parashorea tomentella, satiated seed predators over a large area, while Hopea beccariana and Shorea multiflora only recruited in small isolated clumps. Seed predation experiments suggest that post‐dispersal seed survival was positively density‐dependent in the short‐term. Conclusions: Increased density of flowering conspecifics may contribute to increased likelihood of successful cross‐pollination during low intensity flowering events and, in some cases, to enhanced probability of short‐term seed and seedling survival. Both processes may contribute to the evolution of mast fruiting and general flowering in Southeast Asian lowland dipterocarp forests.

Impacts of logging on density-dependent predation of dipterocarp seeds in a South East Asian rainforest

“…Emergence rates from seeds kept in the laboratory provide a more realistic estimate of invertebrate attack. In the absence of vertebrate predators, insects attacked about 9 per cent of seeds, low in comparison with other studies from the region [25,51]. However, even our laboratory data will probably underestimate insect predation.…”

“…However, Maycock et al [25] also reported negligible survival of other dipterocarp species in the same fruiting event. One possible explanation could be that P. malaanonan seeds are unpalatable.…”

“…However, various seed predators (vertebrates and invertebrates) have been recorded attacking P. malaanonan seeds and seedlings [38,40], so this seems unlikely. Maycock et al [25] suggested that P. tormentella satiated seed predators because a high proportion of trees fruited over a large area. Parashorea species are extremely common in both Danum and Sepilok, and this may partly explain its success outside community-wide mast events.…”

Nonviable seed set enhances plant fitness: the sacrificial sibling hypothesis

“…Hence the number of surviving seeds is a direct function of the number of seeds produced over the ''satiation threshold,'' that is the number of seeds required to satiate seed predators. For large obligately outcrossed and animal-pollinated plants, however, an upper limit on seed production is likely to be imposed by pollinator limitation, which is expected to be severe under the circumstances of mast flowering (Maycock et al 2005). Thus, when the percentage of mature seeds predated by insects or vertebrates prior to dispersal approaches 100%, and in dipterocarps it frequently exceeds 50% (Toy 1991, Nakagawa et al 2005, it seems highly advantageous to increase seed production over the satiation threshold as every seed over this threshold will escape predation.…”

Size-related flowering and fecundity in the tropical canopy tree species, Shorea acuminata (Dipterocarpaceae) during two consecutive general flowerings

“…2d, f) may suggest asymptotic or unimodal relationships rather than linearly increasing ones between tree size and these fecundity parameters. Some external factors such as a lack of cross pollination (Ghazoul et al 1998) and seed consumption by insects and mammals (Chan 1980;Momose et al 1996;Nakagawa et al 2005;Maycock et al 2005) have been reported as being closely related to the pre-dispersal mortality of seeds in various dipterocarp species. However, the relationships between tree size and mature seed production Fig.…”