Local neighborhood and species' shade tolerance influence survival in a diverse seedling bank.

Accumulating evidence suggests that negative density dependence, particularly at early life stages, is widespread in plant communities. We hypothesized that survival in forest seedling banks declines with increasing density of conspecific neighbors and that local-scale effects cause a negative correlation between seedling survival and tree species abundance in the community. We tested these hypotheses using data on 48 956 established seedlings of 235 species over three years in a 50-ha plot in Panama. For all species combined, we found a significant negative effect of conspecific seedling and adult neighbors within 10 m. In species-level analyses, neighbor density affected survival for 45 of 59 species, with effects of conspecifics different from heterospecifics for 29 species. Despite negative effects of local conspecific neighbors, seedling survival tended to be positively correlated with species abundance at the 50-ha scale. However, when accounting for species' shade tolerance, we found a significant negative relationship between seedling survival and species' basal area, but not density, in the 50-ha plot. Our findings indicate that attempts to quantify the contribution of density dependence to tropical tree species coexistence must integrate effects of neighbors across multiple life stages and should also take into account variation in life history strategy.