Interspecific synchrony and asynchrony in the fruiting phenologies of congeneric bird-dispersed plants in Panama

Plants potentially compete for seed dispersal. Selection may favour tempora lly segregated fruiting phenologies to minimize this competition and also t o maintain resident populations of dispersal agents. Alternatively, selecti on may favour temporally aggregated fruiting phenologies when the effective ness of seed dispersal agents varies seasonally or when large, synchronous fruit displays enhance dispersal. These evolutionary scenarios assume that plants share seed dispersal agents. This assumption and temporal overlap in fruiting phenologies were evaluated for the Miconia and Psychotria of cent ral Panama. These two genera accounted for 18 and 27%, respectively, of 109 6 fleshy fruits found in regurgitation or faecal samples taken from 2054 bi rds of 103 species netted in the forest understorey. Two species of manakin s accounted for 62% (123/200) of all Miconia fruit taken. Three species of manakins and three species of migratory thrushes accounted for 97% (282/292 ) of all Psychotria fruits taken. There is a high potential for intrageneri c competition for seed dispersal for both plant genera. Null model analyses showed that the fruiting phenologies of Miconia (14 species) are segregate d in time, while fruiting of Psychotria (21 species) is highly aggregated. The Miconia were found in up to 24% of the diet samples for the two manakin species, suggesting that Miconia may be a critical resource for both speci es. The Psychotria fruited when the diversity of understorey fruits was gre atest, suggesting a high potential for both intra- and extrageneric competi tion. The abundance and nomadism of the six bird species that consumed most Psychotria fruit peaked when the Psychotria fruited, supporting the enhanc ement hypothesis.