Differential seed dispersal patterns generated by a common assemblage of vertebrate frugivores in three fleshy-fruited trees

We analyzed the role of birds and mammals as seed dispersers of 3 fleshy-fruited tree species, hawthorn (Crataegus monogyna), holly (Ilex aquifolium), and yew (Taxus baccata), in a temperate secondary forest in northwestern Spain. Seed dispersal patterns were assessed from direct observations of the disperser birds (thrushes, Turdus spp.), from the collection of bird and mammal defecations; and from seed rain estimates in fixed plots. Some highly specific interactions emerged, especially for the pairs Turdus iliacus-Ilex and T. philomelos-Taxus, due to dispersers' fruit preferences and because some fruit species were more consumed than others. Seeds removed by mammals (mainly fox, Vulpes vulpes, and badger, Meles meles) were deposited in large faecal clumps that were mainly found in open areas, whereas those removed by birds appeared in smaller clumps, located mostly in covered microhabitats. Flocking species (T. viscivorus, T. pilaris, and T. iliacus) flew longer distances after fruit consumption, whereas T. merula and T. philomelos (less gregarious and with resident populations) tended to fly shorter distances, generating a 2-peaked frequency distribution of flight distances. The refuge provided by the tree canopy seemed to be an important cue for the first perch used by birds after leaving the feeding tree. Seed rain of Ilex mainly occurred beneath conspecifics and yews; Taxus seeds were mainly found under conspecifics; and no microhabitat was clearly dominated by Crataegus seeds. In general, this study reveals that similar bird species differed in the quantity and quality (microhabitat and distance travelled) components of their dispersal effectiveness. At the same time, mammals and flocking species emerge as important dispersal vectors implicated in long-distance dispersal.