Tropical rain forest diversity can be maintained through mechanisms that limit seed dispersal. Overstory tree species could filter the arrival of seeds into a community, owing to differences in the resources and habitat that they provide for animal dispersers. The effects of individual tree species in the receiving community on seed arrival are relatively understudied however, given the challenge of interpreting effects of a single overstory species in highly diverse natural forests. In an experiment containing replicated, monodominant, 26-yr-old plantations of four native tree species at La Selva Biological Station (Costa Rica), we studied the effect of the receiving tree species on seed arrival. We collected seed rain of woody species for 14 months from 15 plots with five traps per plot (75 traps). We evaluated whether the 1) arriving seed rain differed in abundance, species richness, diversity and composition among species of receiving overstory trees and 2) receiving tree species differed in attributes. We determined ecological traits of the arriving seed species, including dispersal mode, life form, seed size and successional affinity. We examined relationships between attributes of arriving seed species and receiving tree species and considered the consequences for the trajectory of succession within these four experimental communities.
Results/Conclusions
Across all plots, the total annual seed rain was 133,285 seeds from 118 woody species across 40 families. Abundance and diversity of arriving seeds did not differ among receiving tree species. Species richness and composition did differ however, (P= 0.008 and P = 0.05, R2= 0.216, respectively), owing to the arrival of fewer animal-dispersed seeds into one receiving tree species, Pentaclethra macroloba, a dominant species in nearby old-growth forest. The species composition of both wind- and animal-dispersed seed species differed significantly among receiving tree species (PERMANOVA, Bray-Curtis dissimilarity index, P= 0.01, and Jaccard dissimilarity index, P <0.01, respectively). Tree density and height varied significantly among the receiving tree species, with density highest and height lowest in Pentaclethra macroloba. The successional affinity of the arriving seed species did not vary among receiving tree species although Hieronyma alchorneoides received more tree species seeds classified as secondary-specialists. All four receiving tree species had fewer than five large-seeded late successional species. Seed dispersal into these experimental plots was deterministic, as evidenced by significant correlations between traits of arriving seed species and the receiving community. These results indicate that individual tree species influence community assembly via seed-dispersal filtering of seed dispersed woody species.