Ant visitation (Hymenoptera : Formicidae) to extrafloral nectaries increases seed set and seed viability in the tropical weed Triumfetta semitriloba

摘要

This study tests hypotheses regarding ant protection to plants bearing extrafloral nectaries (EFNs). The hypotheses involve protection against herbivores, increasing both vegetative growth and reproductive output, verifying also the temporal variation of ant presence and aggressiveness. The study was carried out in a tropical weed species, Triumfetta semitriloba, which was planted in an experimental area and followed along the plant cycle. Some plants were treated to exclude ants, and vegetative growth and production of fruits and seeds were compared between treatment and control. The number and aggressiveness of ants visiting EFNs or attending the plants was estimated during the year. Vegetative growth was unaffected by ant presence, although plants attended by ants produced more viable seeds, which reflected upon higher seed germinability. Some ant species visiting EFNs were more aggressive than others, and the number of individuals from these species was higher in the plant pre-reproductive period. The variation of ant density in plants and of their aggressiveness during the year was hypothesized to be related to secretion quality and/or quantity. In the pre-reproductive period the plant may produce a better quality or more nectar, increasing ant visiting and protection of reproductive structures.