Fruit production and predispersal seed fall and predation in Rhamnus alaternus (Rhamnaceae)

In the reproductive cycle of fleshy-fruited plants, and before the seeds are dispersed, some fruits fall down or are predated on the branches. Here, we study the predispersal biology of Rhamnus alaternus in the north-east of the Iberian Peninsula over a 4-year period. Specifically, we examined fruit production, fructification and the phenology of ripening, together with the causes and the consequences of the predispersal loss in female plants. In addition, we evaluated the influence of the biometric traits and the spatial distribution of plants with regard to these aspects. The total estimated fruit production and fruiting phenology varied between localities and years, and there was no relation either to the plant biometry or to the spatial situation. The ripening period was between April and August, with a mean period of fruit permanence on the branches of 102 days. The maximum presence of ripe fruits was from early June to July, 54 days in average after fruit ripening began. The interaction of animals with the fruits has four important consequences: (a) losses in the initial production due to depredation of seeds, mainly by rodents; (b) direct fall of fruit and seeds under the cover of the female plants due to invertebrate predators of pulp; (c) reduction of the period of fruit availability on the branches; and (d) reduction of the proportion of ripe fruits on branches. In summary, the number of seeds available to be dispersed by frugivorous vertebrates is considerably reduced as a consequence of predispersal effects.