Dependence of broad-scale geographical variation in fleshy-fruited plant species richness on disperser bird species richness

Aim We analysed the interdependence of avian frugivore- and fruited plant-species richness at the scale of major river basins across Europe, taking into account several environmental factors along different spatial gradients. Location Continental Europe and the British Isles. Methods We focused on wintering birds and autumn/winter fruiting plants, and used major river basins as geographical units and Structural Equation Modelling as the principal analytical tool. Results The statistical influence of disperser species richness on fleshy-fruited plant species richness is roughly double that of the reverse. Broad-scale variation in frugivore richness is more dependent on environmental factors than on fruited plant richness. However, the influence of disperser richness on plant richness is four times higher than the influence of environmental factors. Environmental influences on both birds and plants are greater than purely spatial influences. Main conclusions Our results are interpreted as indicating that biotic dispersal of fruits strongly affects broad-scale geographical trends of fleshy-fruited plant species richness, whereas richness of fruited plants moderately affects frugivore richness.