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 disperse seeds of Prunus mahaleb, (Rosaceae) were studied in two Southeastern 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 assemblage. Species richness of local bird assemblages ranged between 6 and 26 species. Thrushes, redstarts, and warblers were the main seed dispersers among a total of 31 species recorded for all sites pooled, and together account for 82% of the feeding records. Chaffinches and tits, acting as pulp consumers, were also important in at least two highland assemblages. The proportional similarities for pairwise comparisons among assemblages averaged 0.31+/-0.16, indicative of significant local variation in assemblage composition. However, most differences were between assemblages from the two geographic regions, with pairwise similarities between assemblages within a given region being significant. The relative importance of legitimate seed dispersers, pulp consumers, and seed predators varied significantly among sites, this variation being more pronounced than variability among years within a site. The matrix of proportional similarity among sites showed a structured pattern and was strongly correlated with a matrix of geographic distance among them. The frugivorous birds visiting P mahaleb showed significant similarity and constancy among sites within a region and among years 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 efficiency for individual trees increased in sites or years with greater relative importance of legitimate seed dispersers in the frugivore assemblages. These variations and their potential effects could be very difficult to detect in short-term studies but may have demographic and evolutionary implications in this plant-frugivore interaction.