Recruitment limitation in three large-seeded plant species in a tropical moist forest

Recruitment limitation-the failure of a species to establish recruits at an available site-is a potential determinant of plant communities' structure, causing local communities to be a limited subset of the regional species pool. Recruitment limitation results from three mechanisms: (i) lack of seed sources (i.e., source limitation), (ii) failure of available seeds to reach recruitment sites (i.e., dispersal limitation), and (iii) failure of arrived seeds to establish at a location (i.e., establishment limitation). Here, we evaluated the relative importance of these mechanisms in three co-occurring tree species (Dipteryx oleifera, Attalea butyracea, and Astrocaryum standieyanum) that share seed dispersers/predators. The study was set up on Barro Colorado Island (Panama) at 62 one-ha sites with varying tree densities. Source limitation was estimated as the proportion of sites that would be reached by seeds if seeds were distributed uniformly. Dispersal limitation was estimated from the number of sites with seeds in the soil bank. Establishment limitation was evaluated by measuring germination and 1-year survival in seed addition experiments. The effect of conspecific and heterospecific densities on the mechanisms was evaluated at three spatial scales (1, 5, and 9 ha). For all species, seed predation was the most important recruitment component (similar to 80% decrease in seed survival). Establishment varied among species and was affected by conspecific and heterospecific species densities across spatial scales. Given that species identity, distribution, and seed dispersal/predation affect recruitment at multiple scales, multiscale studies are required to understand how recruitment limitation determines community structure in tropical forests.

Automated summary

Recruitment limitation, which refers to the failure of a species to establish new individuals at an available site, is an important determinant of plant community structure. It is caused by three mechanisms: lack of seed sources, failure of seed dispersal, and failure of seed establishment. This study evaluated the relative importance of these mechanisms in three co-occurring tree species and found that seed predation was the most critical factor affecting recruitment. The ability of seeds to establish varied among species and was influenced by conspecific and heterospecific densities across different spatial scales.