Variação interespecífica dos nectários extraflorais: como o mutualismo de proteção com formigas é regulado em três espécies de Chamaecrista na caatinga?

Abstract

Mutualisms, beneficial interactions of reciprocal exploitation between species, are quite common in nature and participate in critical ecological processes that operate at the most diverse scales, from individuals to ecosystems. In these interactions, the ecological context is a determining component for the result of this association. In this perspective, the present work was set out to investigate how the ant-plant protection mutualism is regulated in three extrafloral nectary bearing We investigated the influence of the size of the extrafloral nectaries on the extrafloral nectar attributes in Chamaecrista duckeana, C. calycioides and C. diphylla, and whether the production of the nectar is induced by herbivory events. Finally, we evaluated whether the ant visitation pattern varies between the three species. species of Chamaecrista (Leguminosae) native to the Brazilian Caatinga. Our hypotheses were: 1) the three species must represent a gradient of availability of food resources via extrafloral nectaries (EFN) for the assembly of local ants; 2) the three species are expected to increase the extrafloral nectary productivity after recent herbivory events, and the species with the largest ENFs must present the greatest control in secretory activity; and 3) ant richness and abundance, especially for the dominant species, must be greater in the species whose extrafloral nectaries are larger and more productive. The study was carried out in an area of Caatinga, in the municipality of PentecosteCE, Brazil, based on 90 focal plants selected in the field, 30 plants of each species of Chamaecrista. In the field, we initially quantified the number of active EFN in all 90 plants. Then, we carried out detailed measurements of the volume and concentration of sugars in the extrafloral nectar of 45 out of the 90 plants (15 plants of each species) and, subsequently, calculated the total mass of sugars. We measured these descriptors at two moments: under field conditions and after inflicting leaf damage. Over the course of two months in the field, we conducted observations and collections of ants visiting the plants on all plants. At the end of the fieldwork, we collected one leaf from each focal plant to measure their size (total area, secretory area and sections) of the EFNs in the laboratory. The results clearly demonstrated that the nectar productivity varies among the three species, being higher in C. duckeana, the species with the largest EFNs. Also, we observed that the simulated herbivory induced increases in the productivity of nectar for all three species, but that the magnitude of the response, mainly of the volume and mass of sugars, was greater for C. duckeana. The diversity and frequency of visitation of the ants varied among the three species of Chamaecrista, being greastes on the plants of C. duckeana. This species proved to be more attractive to the ants of the local assembly, including to the numerically dominant species, due to the higher productivity of theirEFNs. Therefore, it is observed that interspecific differences in the size, productivity and attractiveness of EFNs directly influence the pattern of diversity, the dominance hierarchy of ants and perhaps the quality of protection against herbivores that plants receive.