Disponibilidade de recursos florais e o seu uso por beija-flores em uma área de cerrado de Uberlândia, MG

Abstract

Although hummingbirds are considered an important group of pollinators, few studies about their ecology are available for some ecosystems. The Cerrado biome harbors one of the world richest vascular flora, but at a given community, the proportion of hummingbird pollinated flower is relatively low. Maybe driven by this trend, hummingbird visits are frequently recorded in non-ornithophilous flowers of Cerrado and these opportunistic visits may be crucial for their maintenance. In this sense our study had two aims: 1) to evaluate the floral resource availability for hummingbirds in a typical cerrado area and 2) to estimate the effect of hummingbird visits in the reproduction of a non-ornithophilous plant. In the first part of the study we characterized the assemblage of plants visited by the hummingbirds, the temporal and spatial dynamics of nectar (energy) availability, and factors affecting the frequency of hummingbird visits to the plants. Floral resource availability varied considerably during the year, in synchrony with the flowering of the most abundant species and without clear association with the seasonality typical of the Cerrado. The amount of nectar available per plant individual and the amount of nectar available in the entire area were the factors affecting the frequency of the hummingbird visits. In most of the nonornithophilous plants hummingbirds seemed to act as nectar thieves, since there was no morphological match between pollinator and flower. Nevertheless, in larger flowers and especially in brush flowers the hummingbirds may act as complementary pollinators. In the second part of the study, the effect of hummingbird visits to a non-ornithophilous plant (Styrax ferrugineus) was investigated. In this particular plant, hummingbird seemingly did not contribute directly in the pollination, since contact with the stigma rarely occurred, even though anthers were contacted frequently. Indirect effect of hummingbirds in the plant reproduction seemed to be minimal, since their exclusion from flowers did not affect fruit-set. The inability of hummingbirds in depleting all nectar produced in this mass-flowering plant and the existence of other resource (pollen) for the primary pollinator (large bees) are pointed as possible reasons for the absence of perceptible hindrance of hummingbirds in the plant reproduction. Even though the effect of hummingbird visits for non-ornithophilous plants were not clearly defined, for the bird perspective this opportunistic use of flowers is certainly important, especially in the Cerrado where hummingbird plant diversity is relatively low.