Multiple stage recruitment limitation and density dependence effects in two tropical forests

Recruitment limitation, measured by the failure of some species to arrive and establish in a site, is potentially an important process contributing to the diversity of plant communities. Limited seed production, seed dispersal, and seedling emergence due to abiotic and/or niche-dependent factors result in opportunities for less abundant species to persist. Whereas limitations affecting early phases of plant establishment are relatively well known, the less-examined limitations upon recruitment into more advanced life history stages may also contribute to the maintenance of diversity. We tested this hypothesis by decomposing recruitment limitation into seed limitation, emergence limitation (to seedlings), establishment limitation (saplings) and persistence limitation (adults) in high- and low-diversity communities. We found evidences of recruitment limitation in all ontogenetic stages, but no differences between the examined communities. Limitations in seed, seedling, saplings and adults were explained mainly by abundance in the previous stage. The negative effect of abundance of a given stage on the abundance of the next stage (negative density-dependent plant establishment) was more evident in the high diversity community. There was a reduction in species’ abundance and an increase in species richness from the seed to the adult stages, resulting in an increase in the evenness along ontogenetic stages in both communities; in all stages, the high-diversity community was richer than the low-diversity community. We found evidence that recruitment limitation operates at multiple stages and is density dependent in these two tropical forests. Our results also suggest that these effects may be stronger in the high-diversity community. Thus, recruitment limitation mediated by density dependence across multiple ontogenetic stages has to be considered in future studies of factors maintaining diversity in tropical forests.