| This dissertation is concerned with evaluating the nature of the interactions between Schomburgkia tibicinis (Orchidaceae) and a series of organisms (i.e., ants, bees, wasps, beetles, mealybugs) that inhabit the coastal sand dune vegetation of the State of Yucatan, Mexico. The objectives are: study the pollination biology of the orchid, assess the existence and the effect of an ant-guard type system on the reproductive fitness of the orchid, and determine the uptake by the orchid of organic material provided by the ants.;S. tibicinis harbors nine ant species in its hollow pseudobulbs; five of them are common (Crematogaster brevispinosa, Camponotus planatus, C. abdominalis, C. rectangularis, and Ectatomma tuberculatum), and interact readily with the orchid. The plant and the ants show a significant clumped distribution along the coast.;The orchid's reproductive season is from January to June, and pollination is accomplished by Eulaema polychroma (Euglosini). The results obtained, i.e., few visits by pollinators and increased fruit production with hand pollination, are clear evidence to demonstrate that the low fruit set (0.02 fruit/flower ratio) is a consequence of pollinator limitation, due to the pollination system: "mimicry based on naivete".;The results of the experiment set to demonstrate if ants were functioning as plant-guards against herbivores, mainly Stethobaris sp. (Curculionidae), follow four clear tendencies: (1) ant presence is not synonymous with benefit to the plant; (2) lowest fruit production and highest inflorescence damage are significantly associated with the control (no ants) and the smaller ants (C. brevispinosa and C. planatus), and these interactions are of an antagonistic nature; (3) maximum fruit production and minimum inflorescence damage are significantly associated with the larger ant species (C. rectangularis and E. tuberculatum), and these interactions are clearly mutualistic; and (4) The increase in ant size tends to have a positive effect on the plant's reproductive output (higher fruit set).;The results of the nutrient uptake experiment are compelling evidence for uptake, translocation and incorporation of nutrients from exogenously provided organic material they further demonstrate that the organic debris deposited by the ants on the internal surface of the orchid pseudobulbs are incorporated by the plant in the manner of a reversed animal-plant interaction (mutualism). These exogenous nutrients would help the plant to survive on the nutrient-poor dune soils. |
