Generalization versus specialization in plant pollination systems

The long-standing notion that most angiosperm flowers are specialized for p ollination by particular animal types, such as birds or bees, has been chal lenged recently on the basis of apparent widespread generalization in polli nation systems. At the same time, biologists working mainly in the tropics and the species-rich temperate floras of the Southern hemisphere are docume nting pollination systems that are remarkably specialized, often involving a single pollinator species. Current studies are aimed at understanding: (I )the ecological forces that have favoured either generalization or speciali zation in particular lineages and regions; (2) the implications for selecti on on floral traits and divergence of populations; and (3) the risk of coll apse in plant-pollinator mutualisms of varying specificity.