POLLINATION ECOLOGY OF FOUR DALECHAMPIA SPECIES (EUPHORBIACEAE) IN NORTHERN NATAL, SOUTH AFRICA

Abstract

The pollination ecology of four Dalechampia species was studied in three areas in northern Natal, South Africa. All species were pollinated by resin‐ and/or pollen‐collecting megachilid bees (Hymenoptera: Megachilidae). The most common of these at all study sites was Heriades sp. (Megachilini), which collected both pollen and resin. This bee was the primary pollinator of D. galpinii and D. volubilis, and a secondary pollinator of D. aff. parvifolia and D. capensis. The primary pollinators of these latter two Dalechampia were Pachyanthidium near cucullatum and P. cordatum (Anthididiini), respectively. These are larger bees that collected mainly resin. Other visitors varied among Dalechampia species and among sites. Pairs of Dalechampia species were often found in sympatry (within 30 m of each other) and shared pollinators to varying extents. “Transfer experiments,” in which we placed inflorescences of two Dalechampia species together, reinforced observations of flower discrimination by bees foraging among naturally occurring sympatric pairs. Heriades sp. showed no obvious discrimination between Dalechampia species, but Pachyanthidium spp. “preferred” the Dalechampia species with the greater resin reward. Occasionally, however, Pachyanthidium would visit less rewarding species. Thus, although sympatric African Dalechampia species showed some pollinator partitioning, it was much weaker than found among New World species, and cannot alone explain the general absence of Dalechampia hybrids in northern Natal.