Floral Specialization: what do floral attributes and floral visitors tell us?

Floral traits may either facilitate or constrain the gathering of food resources by certain animals. We therefore sought here to define the floral specialization levels of 19 plant species visited by foraging insects, based on their floral attributes and on the behaviors of their respective insect visitors. Based on those two criteria the degree of specialization of each plant-pollinator system was determined. The species studied had eight types of flowers (open, gullet, capitulum, opened with oil-secreting glands, opened with poricidal anthers, brush, tubular, and transition between open and deep polypetalous), and showed a continuum of pollination systems, from the more specialized levels to the most generalized. The most specialized species were visited predominantly by functional group of efficient pollinators, whereas the most generalist species received visitors of four or five functional groups, but they did not act as efficient pollinators. Furthermore, in the more generalist species it was not possible to characterize the floral visitors as pollen vectors or thieves/pillagers of resources. The parts of the insect bodies that transfer pollen to the floral stigmas can be grouped into five regions: the dorsal region of the thorax, the ventral region of the thorax and abdomen, the frontal region of the head, and the tibia and dorsal region of the abdomen. Plants evidencing even the highest levels of floral specialization can nonetheless be visited by floral resource thieves and/or robbers – indicating that floral specialization in itself is not capable of eliminating floral visitors prejudicial to plant reproduction.