Efeitos do roubo de néctar em um sistema de polinização tropical: quantificando as implicações para a planta e para os visitantes florais

Abstract

Nectar robbery can be important, whether direct or indirectly, for structuring interaction networks between plants and its floral visitors. The effects of this behaviour on the reproduction of plant species primarily depend on factors related to the life history of the plant species itself and the dynamics of floral visitors, while the effect on the foraging dynamics of floral visitors generally occurs through depletions in nectar. In this study, two manipulative experiments were conducted to quantify the effects of nectar robbery by hummingbirds on the female fitness of an ornithophilous plant species, Heliconia spathocircinata, and on the foraging of floral visitors. Additionally, a deterministic model, based on the results obtained in the experiments, was proposed to simulate the implications for the interaction system, given the differences in the behavioural choices of floral visitors, displaying mixed foraging tactics in the studied system. The results highlighted that H. spathocircinata was highly self-compatible in the studied population, and the effect of nectar robbery ws neutral, while cross-pollination has a negative impact on the female fitness of this plant species. Regarding the effect on the activity of floral visitors, the dynamics were minimally altered concerning legitimate and illegitimate visitation activities, but it showed that hummingbirds seem more inclined to choose situations with little nectar robbery for foraging. The proposed conceptual model demonstrated that when one foraging behaviour is more favoured than another by the visitor, the favoured and unfavoured behaviours oscillate in different orders of magnitude. However, when both are equally chosen, they fluctuate in similar orders of magnitude. These results suggest that autogamy in H. spathocircinata may have evolved from its high self-compatibility and, possibly, from pollen limitation, especially in locations where nectar robbery is a significant part of the interactions. It is also possible that the neutral effect of nectar robbery in hummingbird foraging is due to the high unpredictability of nectar resource availability in H. spathocircinata in the study area, rather than the level of robbery itself. As the foraging choice of visitors varies between legitimate and illegitimate visits in the studied system, the costs of these two behaviours may be similar or even equal. In this context, nectar robbery could function as commensalism in the H. spathocircinata – hummingbirds system.