ANT POLLINATION OF THE PALAEOENDEMIC DIOECIOUS BORDEREA-PYRENAICA (DIOSCOREACEAE)

The importance of ants for pollination In the dioecious Borderea pyren aica (Dioscoreaceae), a Tertiary palaeoendemic plant of the Pyrenees ( NE Iberian Peninsula) was studied. The frequency of different visitors (ants; lady beetles, and Diptera) to staminate and pistillate flowers was quantified, and their effectiveness as pollinators was examined b y means of fruit and seed set in selective experimental exclusions. Al though ants were less abundant on flowers than other visitors, they we re the most effective pollinators. Some qualitative factors of this mu tualistic ant-plant interaction may account for their effectiveness: t he small size of the ants, their high visitation rate to pistillate fl owers, and the lack of reduction in viability of the pollen transporte d on the integument. In addition, the sedentary nature of ants assures their presence during the flowering period. The most abundant floral visitors of B. pyrenaica were therefore not the most effective pollina tors.