Spatial and temporal patterns of seed attack and germination in a large-seeded neotropical tree species

It has long been argued that seed dispersal enhances recruitment in tropica l trees by allowing offspring to 'escape' strong density/distance-dependent attack by insects, pathogens and rodents. Here we examined the effects of canopy openness and parent-offspring distance upon the frequency and timing of Chlorocardium rodiei seed attack and germination within a 15-ha plot of Guyanan tropical rain forest. Seeds were artificially dispersed beneath pa rent tries, in the understorey away from trees and in gaps. Analysing our d ata from an 85-week period of regular monitoring, we found that the main sp atial gradients, canopy openness and distance to nearest adult conspecific, do not lead to differences in the final number of seeds attacked by infest ing scolytid beetles or rodents, The timing of beetle attack, however, vari ed along the distance gradient and this difference affords seeds at further distances a 'window' in which to germinate and produce a seedling before a ttack. Canopy openness was not a good predictor of rooting success, but dis tance was strongly associated with root and shoot formation success and the mean time to shoot formation. There was a strong negative effect of distan ce on the likelihood of a seed being colonised by scolytid beetles prior to removal by rodents and shoot failure was strongly associated with prior in festation. We believe these results bring a key point to bear on the well-e stablished notion of distance-dependent attack on seeds in tropical rainfor ests, viz. that seed characteristics (size, germination syndrome) and the t iming of attack may be more important in explaining patterns of early seedl ing recruitment than distance. Our studies suggest that advantages accrued through dispersal in species like Chlorocardium will depend heavily on the 'race' between seed germination and attack. In the case of Chlorocardium, t he 'race' can be lost at considerable distances due to its prolonged dorman cy and the temporal fluctuations in fruitfall and rainfall which influence attack and germination. The results presented here suggest that the lag bet ween seed attack and germination in tropical trees can regulate the influen ce of parent-offspring distance on cohort recruitment at this life history stage.