Production of copious dilute nectar in the bird-pollinated African succulent Aloe marlothii (Asphodelaceae)

Aloe marlothii is a CAM succulent plant which is widespread in the northern and north-eastern summer rainfall region of South Africa. Flowering occurs during dry winter months (June–September) and the large inflorescences attract a wide range of birds. Flowering phenology and nectar production were studied during three seasons (2005–2007) at a dense population of aloes in Suikerbosrand Nature Reserve. Three flower stages were recognised; 1) immature phase, 2) male phase, and 3) female phase, with extremely high nectar volumes (mean = 248 µl/flower) in stage 2, the stage to which most avian visitors are attracted. Nectar sugar concentration was very low (12% w/w) in stage 2 when the volume was highest. Comprehensive nectar volume and concentration data were gathered and showed little daily variation, despite a 24 h temperature range of up to 20 °C. The extremely high volume and low concentration of the nectar proved to be consistent with a generalist bird pollination syndrome. A wide range of avian visitors (42 species; 59% of the resident bird community recorded during flowering) fed on nectar throughout the day, but a decrease in nectar standing crop was only evident at midday. Chacma baboons Papio hamadryas ursinus foraged on nectar and caused significant inflorescence damage.