Maruyama Pietro K, Oliveira Genilda M, Ferreira Carolina, Dalsgaard Bo, Oliveira Paulo E
Instituto de Biologia, Universidade Federal de Uberlândia (UFU), Cx. Postal 593, CEP 38400-902, Uberlândia, MG, Brazil,
Naturwissenschaften. 2013 Nov;100(11):1061-8. doi: 10.1007/s00114-013-1111-9. Epub 2013 Nov 16.
Generalization prevails in flower-animal interactions, and although animal visitors are not equally effective pollinators, most interactions likely represent an important energy intake for the animal visitor. Hummingbirds are nectar-feeding specialists, and many tropical plants are specialized toward hummingbird-pollination. In spite of this, especially in dry and seasonal tropical habitats, hummingbirds may often rely on non-ornithophilous plants to meet their energy requirements. However, quantitative studies evaluating the relative importance of ornithophilous vs. non-ornithophilous plants for hummingbirds in these areas are scarce. We here studied the availability and use of floral resources by hummingbirds in two different areas of the Cerrado, the seasonal savannas in Central Brazil. Roughly half the hummingbird visited plant species were non-ornithophilous, and these contributed greatly to increase the overall nectar availability. We showed that mean nectar offer, at the transect scale, was the only parameter related to hummingbird visitation frequency, more so than nectar offer at single flowers and at the plant scale, or pollination syndrome. Centrality indices, calculated using hummingbird-plant networks, showed that ornithophilous and non-ornithophilous plants have similar importance for network cohesion. How this foraging behaviour affects reproduction of non-ornithophilous plants remains largely unexplored and is probably case specific, however, we suggest that the additional energy provided by non-ornithophilous plants may facilitate reproduction of truly ornithophilous flowers by attracting and maintaining hummingbirds in the area. This may promote asymmetric hummingbird-plant associations, i.e., pollination depends on floral traits adapted to hummingbird morphology, but hummingbird visitation is determined more by the energetic "reward" than by pollination syndromes.
花与动物的相互作用中普遍存在泛化现象，尽管动物访客并非同等有效的传粉者，但大多数相互作用可能对动物访客来说是重要的能量摄入途径。蜂鸟是以花蜜为食的 specialists，许多热带植物专门适应蜂鸟传粉。尽管如此，尤其是在干燥和季节性的热带栖息地，蜂鸟可能经常依靠非鸟媒植物来满足其能量需求。然而，在这些地区评估鸟媒植物与非鸟媒植物对蜂鸟相对重要性的定量研究却很匮乏。我们在此研究了巴西中部季节性稀树草原塞拉多两个不同区域中蜂鸟对花卉资源的可利用性和利用情况。大约一半被蜂鸟访花的植物物种是非鸟媒植物，这些植物极大地增加了花蜜的总体可利用性。我们表明，在样带尺度上，平均花蜜供应量是与蜂鸟访花频率相关的唯一参数，比单花和植株尺度上的花蜜供应量或传粉综合征更具相关性。利用蜂鸟 - 植物网络计算的中心性指数表明，鸟媒植物和非鸟媒植物对网络凝聚力的重要性相似。这种觅食行为如何影响非鸟媒植物的繁殖在很大程度上仍未得到探索，可能因具体情况而异，然而，我们认为非鸟媒植物提供的额外能量可能通过吸引并留住该区域的蜂鸟来促进真正鸟媒花的繁殖。这可能会促进不对称的蜂鸟 - 植物关联，即传粉取决于适应蜂鸟形态的花部特征，但蜂鸟的访花更多地由能量“回报”而非传粉综合征决定。
