SPATIAL AND TEMPORAL VARIATION IN THE AVIAN-FRUGIVORE ASSEMBLAGE OF PRUNUS MAHALEB - PATTERNS AND CONSEQUENCES

The patterns of spatial and temporal variation in the species richness and relative abundance of frugivorous birds that consume fruits and d isperse seeds of Prunus mahaleb, (Rosaceae) were studied in two Southe astern Spain populations and compared with previous information from 4 sites, 3 of them in Northwestern Spain. Data for 8 study years in one population are used to assess temporal variation in this frugivore as semblage. Species richness of local bird assemblages ranged between 6 and 26 species. Thrushes, redstarts, and warblers were the main seed d ispersers among a total of 31 species recorded for all sites pooled, a nd together account for 82% of the feeding records. Chaffinches and ti ts, acting as pulp consumers, were also important in at least two high land assemblages. The proportional similarities for pairwise compariso ns among assemblages averaged 0.31+/-0.16, indicative of significant l ocal variation in assemblage composition. However, most differences we re between assemblages from the two geographic regions, with pairwise similarities between assemblages within a given region being significa nt. The relative importance of legitimate seed dispersers, pulp consum ers, and seed predators varied significantly among sites, this variati on being more pronounced than variability among years within a site. T he matrix of proportional similarity among sites showed a structured p attern and was strongly correlated with a matrix of geographic distanc e among them. The frugivorous birds visiting P mahaleb showed signific ant similarity and constancy among sites within a region and among yea rs within a site, but subtle variations in the relative importance of legitimate seed dispersers versus non-disperser species had measurable effects on seed dispersal. Average fruit removal and seed dispersal e fficiency for individual trees increased in sites or years with greate r relative importance of legitimate seed dispersers in the frugivore a ssemblages. These variations and their potential effects could be very difficult to detect in short-term studies but may have demographic an d evolutionary implications in this plant-frugivore interaction.