Pollination and seed dispersal in the endangered succulent Euphorbia brevitorta.

Abstract

The dwarf succulent euphorbia Euphorbia brevitorta (Euphorbiaceae) is a localized and potentially threatened endemic species with limited distributed across rocky grasslands in central and southern Kenya. The pollination ecology and seed dispersal of E. brevitorta was investigated by direct observation. Euphorbia brevitorta relies on pollinators for fruit-set as it bears separate male and female flowers on the same plant, but appears to be self-compatible. Euphorbia brevitorta was found to have a generalist pollination system, with insects being the main pollinators. Pollinators of E. brevitorta comprise a wide range of insects from three different orders: true flies (Diptera), ants, bees and wasps (Hymenoptera) and beetles (Coleoptera). Flies, wasps and honeybees were found to be the most efficient transporters of pollen between different individual plants and carried the highest volumes of pollen. Observations of pollinators revealed adequate pollination and high visitation rates by pollinators. Seed dispersal was found to occur in two stages: localized dispersal from explosive capsules up to~2 metres from the plant, followed by limited secondary dispersal by ants further away. Euphorbia brevitorta relies on both pollinators and seed dispersal for adequate recruitment and survival in its natural habitat.

Keywords: pollination, seed dispersal, Euphorbia, cyathia, ant-plant interactions, Euphorbiaceae, Hymenoptera, Diptera, Coleoptera.