Implicaciones ecológicas y evolutivas del robo de néctar en ecosistemas neotropicales venezolanos

Resumo

Some nectarivorous animals have developed ways of evading the morphological constraints of flowers to non-pollinating visitors, these are known as nectar robbers. These animals perform perforations in the corolla or use an existing perforation to directly access the nectar. In this process they usually do not contact the reproductive structures of the flower and as a result do not pollinate the plants. Although the nectar robbing is common in angiosperms, it has been underestimated as a relevant agent for the reproduction and evolution of flowering plants. However, recent evidence shows the relevance of the robbers for the reproductive success of some plant species. The objective of this dissertation is to study and compare the ecological and evolutionary implications of the nectar robber by birds of the genus Diglossa (Thraupidae) at various levels in Neotropical high mountain ecosystems in Venezuela. To do this, a bibliographical review was initially carried out, on the plant-animal interactions in the Páramos (Neotropical high mountain ecosystem) and a diagnosis of their information gaps, we explored the behaviour of the flowering phenology of a high number of plant species and their pollinator network. Secondly, we analysed the characteristics of plants with tubular flowers, which are correlated with the nectar robbinn by species of Diglossa, in three ecosystems of high Andean mountain (sub-páramo forest, Andean páramo and high Andean páramo). Thirdly, we analysed the ecological implications of the nectar robbing by species of Diglossa, in the fitness of Castilleja spp. (Orobanchaceae), in a wide altitudinal gradient (2700-4600 m asl). Finally, we evaluated the evolutionary implications of the nectar robbing by species of Diglossa, in floral structures of the Tacsonia group (Passiflora, Passifloraceae), plants of Andean distribution. We can generalize, that the study of plant-animal interactions in the páramos is a field with large information gaps. However, herbivory interactions, pollination and seed dispersion are registered. On the other hand, the phenology of the plants of the Venezuelan páramo guarantees that there are few species with offer for the nectarivorous fauna throughout the year and marked peaks of flowering at the entrance and exit of the humid season. The most important pollinators of the páramo plants are bumblebees (Bombus spp.) and hummingbirds. The robbery of nectar by species of Diglossa is very common in the ecosystems of high mountain Andean Venezuelan, there is an uncoupling with the flowers whose corollas are greater than 20 mm, which tend to have great rewards of nectar, to be lower flower aggregation, to present colourful colours, to possess resistance to the piercing of flowerpiercers bill and to be associated with shrubs or rocks that are used as perches by these birds, to carry out the robbery. The effect of the nectar robbery on the fitness of Castilleja spp. is neutral, although its incidence are very variable spatially and temporally. Finally, the robbery of nectar by species of Diglossa, in the species of Tacsonia (Passiflora), does not affect the fruitseed and seed/ovule ratio of their species, we not found evolutionary correlation between their floral traits and the levels on nectar robbing.