Pollination ecotypes of Satyrium hallackii (Orchidaceae) in South Africa

Abstract

Intraspecific variation in floral traits may reflect adaptive shifts in the pollination system of a plant. This idea was tested by examining the pollination biology of Satyrium hallackii H. Bolus., an orchid which has spurs varying from 8 to 36 mm among populations in southern Africa. Field observations showed that the short-spurred form (S. hallackii subsp. hallackii) in coastal fynbos habitats is pollinated by bees, while the long-spurred form (S. hallackii subsp. ocellatum) in grassland habitats is pollinated primarily by hawkmoths and, secondarily, by long-tongued flies. The shift between hawkmoths and bees as pollinators may have been promoted by an ecological gradient in South Africa: carpenter bees are common in coastal fynbos habitats, but rare in grassland habitats where there are few available nesting sites. On the other hand, hawkmoths are common in grassland habitats, but rare in fynbos where there are few palatable host-plants. The formation of pollination ecotypes across pollinator gradients has probably been a major factor in the diversification of South African plants with specialized pollination systems.