Two-stage dispersal of Guarea glabra and G. kunthiana (Meliaceae) in Monteverde, Costa Rica

Seed dispersal of Guarea glabra and G. kunthiana (Meliaceae) in Monteverde, Costa Rica was studied to determine how seed predation and secondary dispersal affect the distribution of seeds available for recruitment. The arillate seeds are consumed mainly by birds that regurgitate or defecate the seeds intact. After dispersal, 45.6% of G. glabra and 26.6% of G. kunthiana seeds were buried 1–3 cm in the soil, presumably by scatterhoarding rodents such as agoutis (Dasyprocta punctata). G. glabra seeds that were not cached were eaten mostly by beetles, and 33.7% of the seeds remained cached after 12 wk. The cached G. glabra seeds did not germinate, however, perhaps as a result of experimental procedures used to mark the seeds. In greenhouse experiments, G. glabra seeds buried to mimic scatterhoarding had higher germination success than seeds on the soil surface. G. kunthiana seeds not cached were eaten by peccaries (Tayassu tajacu) and other seed predators (60%) or were inviable (10%). Only nine (7.5%) viable G. kunthiana seeds remained in caches after 12 wk. Secondary dispersal resulted in a rearrangement of the seed shadow. G. glabra seeds were moved to sites with less leaf litter and lower vegetation density, while G. kunthiana seeds were moved farther from conspecific trees and closer to fallen logs during secondary dispersal. Considering the high rates of seed predation in the field for both species, the germination advantages for G. glabra in the greenhouse, and the shifts in microhabitat during scatterhoarding, it is likely that secondary dispersal by scatterhoarding rodents is an important stage in Guarea recruitment.RESUMEN. Dispersion de semillas de Guarea glabra y G. kunthiana (Meliaceae) en Monteverde, Costa Rica fureon examinadas para determinar como la predacion de semillas y dispersion secundaria afectan la distribucion de semillas disponibles para recrutamiento. Las semillas ariladas son consumidas principalmente por aves que regurgitan o defecan la semilla intacta. Luego de dispersion, 30–45% de las semillas fueron enterradas 1–3 cm en el suelo, posiblemente por roedores que disperan y acumulan como al agouti (Dasyprocta puncaata). Semillas de G. kunthiana que no fueron escondidas fueron comidas por pecaris (Tayassu tajacu) y otros predadores de semillas (60%) o no fueron viables (10%). Solo neuve (7.5%) semillas viables de G. kunthiana permanecieron en los escondites luego de 12 semanas. En contraste, semillas de G. glabra que no fueron escondidas fueron comidas mayormente por escarabajos que por pecaris, y 33.7% de las semillas permanecieron escondidas luego de 12 semanas. Las semillas esconditas de G. glabra enterradas para imitar dispersion y acumulion tuvieron una germinacion mayor que semillas en la superficie del suelo. Dispersion secundaria resulto en un rearreglo de la sombra de semillas. Las dos especies experimentaron un leve aumento neto en la distancia promedio de conspecificos en frutos luego de dispersion y acumulacion. Semillas de G. kunthiana fueron movidas cerca de troncos caidos durante dispersion secundaria, mientras semillas de G. glabra fueron movidas a lugares con menos lecho de hojas y baja densidad de vegetacion. Considerando la alta proporcion de predacion de semillas en el campo para ambas especies, la ventaja de germinacion de G. glabra en el invernaculo, y el cambio en micrambiente durante dispersion y acumulacion, es posible que dispersion secundaria por roedores que dispersan y acumulan es importante in etapas de recrutamiento en Guarea.