Ritmo circadiano do florescimento de Melocactus zehntneri: quem seriam os potenciais visitantes e polinizadores

Abstract

Resources in Caatinga vary with the seasonality of the region and are less abundant during the dry season. In this period, few plants are flowering, among them a few Cactaceae, so there are few resources for nectarivorous. For this reason, opportunists can visit them and steal nectar. This work will describe the circadian cycle, the nectar production and pattern of secretion, consumption and visitation in Melocactus zehntneri, seeking possible explanations about the interactions between this cactus and bats (Glossophaga soricina, Lionycteris spurelli, Lonchophylla sp. and Xeronycteris vieirai) in the Caatinga of Lajes do Cabugi / RN. Recently, a parallel study has reported that these bats are visiting this cactus because large amount of pollen of the species was found in their hairs or feces. But their flowers do not indicate signs of chiropterophily, therefore data were collected in the field and an experiment was carried out to investigate the existence of floral rewards and responses in the circadian cycle and in the pattern of nectar secretion, related to this interaction. The volume and concentration of sugar in the nectar decreased after 5:30 pm, but it continues with quality to compensate nocturnal pollinators that begin to forage at that time, such as small bats that live in Caatinga. Hummingbirds are the most efficient pollinators of M. zehntneri, and probably they’re sharing the nectar with other floral visitors, including bats of the region. There is a change in the pattern of nectar secretion before and after at 17:30 pm, which may be associated to interactions with floral visitors of this species. This fact may increase the genetic variability in the population of the cactus, since it would also benefit from other floral visitors besides the hummingbirds which show a very territorialist behavior. In addition, bats may be using the nectar of this plant as an alternative source of energy in the dry season of the Caatinga, because the resources are scarcer.