The impact of an invasive ant, Linepithema humile (Mayr) (Hymenoptera: Formicidae), on the dispersal of the elaiosome-bearing seeds of six plant species
Linepithema humile has invaded pristine areas in the Western Cape Province, South Africa, displacing important myrmecochorous ant species. The impact of this invasion on the dispersal of six species of elaiosome-bearing seeds varying in size, shape and mass was investigated. Linepithema humile failed to disperse heavy elaiosome-bearing seeds, although it readily removed lighter seeds like those of Polygala myrtifolia. This suggests that areas dominated by small ant species like L. humile would be characterized by low dispersal rates for heavy seeds. Indigenous ants in areas uninvaded and invaded by L. humile did not respond equally well to six elaiosome-bearing seeds. More of the heavier Leucospermum cordifolium than the lighter Pudalyria calyptrata and Paranomus reflexus seeds were removed by ants in uninvaded areas. In invaded areas the heavier P. myrtifolia seeds were dispersed more readily than the lighter Agathosma ovata seeds. There was no indication of any specificity in the seed-ant interaction because the introduced ant, L. humile, dispersed smaller seeds. In addition, R calyptrata, which occurs naturally in the study area, was not taken preferentially to other species of seed by myrmecochorous ants.