The impact of an invasive ant, Linepithema humile (Mayr), on the dispersal of Phylica pubescens Aiton seeds in South Africa
Myrmecochory, or seed dispersal by ants, is a mutualistic plant-ant interaction common to the fire-prone shrublands of the southwestern Cape, South Africa. Elaiosome-bearing seeds are located rapidly by ants and transported to nests where they are protected from granivorous rodents, desiccation and fire. This interaction is threatened by the invasive Argentine ant, Linepithema humile, which has displaced important myrmecochorous ant species in previously undisturbed areas. The impact of this infestation was assessed. Linepithema humile, which was active mainly at night, dispersed few seeds and removed most of the elaiosomes in situ. The majority of seeds were dispersed from invaded areas during the day by two indigenous species of ants, Tetramorium quadrispinosum and Ocymyrmex cilliei. Dispersal in uninvaded areas occurred mainly between 19:00 and 21:00 but was generally spread overa 24-hour period, indicating the participation of a complex of ant species. Significantly more seeds were dispersed in uninvaded areas than in areas invaded by L. humile. In invaded areas, there were no significant differences in the numbers of seeds dispersed by ants and the numbers eaten by rodents. In contrast, significantly more seeds were dispersed by ants than were eaten by rodents in uninvaded areas.