Seed mass, seedling emergence, and environmental factors in seven rain forest Psychotria (Rubiaceae)

We examined the effects of seed mass on performance between the time of see d dispersal and emergence within seven sympatric rain forest woody species of Psychotria in two contrasting natural habitats: gaps and shaded forest. We determined the: effects of seed mass on emergence (the total proportion of emerged seedlings) and on the speed of emergence (the time necessary to reach 50% total emerged seedlings) in both greenhouse and field conditions, and we observed the effects of seed mass on the risk of removal by animals in the held. The effects of seed mass on performance were specific to spec ies and habitat. For example, in two species, seed mass had a positive effe ct on emergence. while another showed a negative effect; for most of the sp ecies, effects on performance restricted to only one habitat (shaded forest or gap). Similarly, the results for effects of seed mass on the risk of re moval were species- and habitat-specific. In the greenhouse, seed mass did not affect either emergence or the speed of emergence under either high or low light conditions. Our results suggest that: (i) seed mass did not have a general effect on emergence success and (ii) the effects of seed mass on seedling emergence are driven by external ecological factors more than by i ntrinsic effects of seed mass. Seed-removing animals appear to be an import ant ecological agent operating on intraspecific seed mass variation.