Response of recruitment to light availability across a tropical lowland rain forest community

1.  Many hypotheses about species coexistence involve differential resource use and trade-offs in species' life-history traits. Quantifying resource use across most species in diverse communities, although, has seldom been attempted.
2.  We use a hierarchical Bayesian approach to quantify the light dependence of recruitment in 263 woody species in a 50-ha long-term forest census plot in Panama. Data on sapling recruitment were obtained using the 1985–1990 and 1990–1995 census intervals. Available light was estimated for each recruit from yearly censuses of canopy density.
3.  We use a power function (linear log–log relationship) to model the light effect on recruitment. Different responses of recruitment to light are expressed by the light effect parameter b . The distribution of b had a central mode at 0.8, suggesting that recruitment of many species responds nearly linearly to increasing light.
4.  Nearly every species showed increases in recruitment with increasing light. Just nine species (3%) had recruitment declining with light, while 198 species (75%) showed increasing recruitment in both census intervals. Most of the increases in recruitment were decelerating, i.e. the increase was less at higher light ( b  < 1). In the remaining species, the response to light varied between census intervals (24 species) or species did not have recruits in both intervals (41 species).
5.   Synthesis. Nearly all species regenerate better in higher light, and recruitment responses to light are spread along a continuum ranging from modest increase with light to a rather strict requirement for high light. These results support the hypothesis that spatio-temporal variation in light availability may contribute to the diversity of tropical tree species by providing opportunities for niche differentiation with respect to light requirements for regeneration.