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| 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. nonornithophilous
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 nonornithophilous,
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 nonornithophilous
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. | |
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