Effect of different ant species on reproductive fitness of Schomburgkia tibicinis (Orchidaceae)

We studied the effect of four ant species on the reproductive fitness (number of fruits produced)of Schomburgkia tibicinis (Orchidaceae), in the coast of Yucatan, Mexico. Ants forage day and night for the nectar produced by the reproductive structures of the orchid. Ant size is: Camponotus planatus (3-4 mm), C. abdominalis (4~6 mm), C. rectangularis (7-9 mm), and Ectatomma tuberculatum (9-12 mm). The results indicate that ant efficiency in disrupting the activities of the main herbivore, (Stethobaris sp./Coleoptera)varies, and that it is apparently related to ant size, three tendencies are clear: (a)lowest fruit production and highest inflorescence damage are significantly associated with the smaller ants and the control; (b)maximum fruit production and minimum inflorescence damage are significantly associated with the larger ant species; and (c)the increase in ant size tends to have a positive effect on the plant's reproductive output (less dead spikes and more matured fruits). We discuss ant effect on the pollination of the orchid, and emphasize that ant presence should not be associated, in general, with benefit to plants.