Differences in pollination systems between temperate and tropical areas have been known for a long time. Wind pollination is practically absent in the tropics, whereas vertebrate pollinators are more common. In addition, many peculiar pollination systems such as pollination by ovule parasites are much more successful in the tropics. Probably because of such characteristics, plant pollinator interactions in the tropics had once been considered more specialized, but recent studies indicate an opposite trend. However, the causes for the differences have not yet been explained. In this presentation, how the balance of supply and demand of pollination services affect plant–pollinator interactions is discussed, and how observations in the tropics are consistent with the situation expected when pollination is limited is suggested. Further, possible factors that limit the supply of pollination service in the tropics are examined, and finally, how this hypothesis can be tested and the future direction of the study are discussed.