PLANT-VERTEBRATE SEED DISPERSAL SYSTEMS IN THE MEDITERRANEAN - ECOLOGICAL, EVOLUTIONARY, AND HISTORICAL DETERMINANTS

Investigations on vertebrate seed dispersal systems in the Mediterrane an show that extremely efficient plant-disperser mutualisms do not req uire, and thus are not evidence for, mutual evolutionary adjustments o f participants, Current Mediterranean dispersal systems have apparentl y been shaped by means of 1, trophic and behavioral adaptations of bir ds morphologically preadapted to pre-existing plant resources, and 2. disperser-mediated processes of habitat-shaping occurring at an ecolog ical time scale. These processes depend on differential recruitment of plant species as a function of disperser preferences, rather than on adjustments based on evolutionary processes. On the plant side, there is a prevalence of historical and phylogenetic effects, which reflects a series of ecological limitations inherent to the interactions betwe en plants and dispersal agents that constrain plant adaptation to disp ersers. To test adaptive hypotheses and explanations, future investiga tions on Mediterranean plant-disperser systems should concentrate more on the animal than on the plant side of the interaction.