Ecological fitting is a sufficient driver of tight interactions between sunbirds and ornithophilous plants

1.  Plant-bird pollination interactions evolved independently on
different continents. Specific adaptations can lead to their restriction
when potential partners from distant evolutionary trajectories come into
contact. Alternatively, these interactions can be enabled by convergent
evolution and subsequent ecological fitting. 2. We studied the
interactions between New World plants from the genus Heliconia, Asian
plants of genus Etlingera and African sunbirds on a local farm in
Cameroon. Heliconia evolved together with hummingbirds and Etlingera spp.
with spiderhunters - an oriental subgroup of the sunbird family. 
3. Sunbirds fed on all studied plants and individual plant species were
visited by a different sunbird spectrum. We experimentally documented a
higher number of germinated pollen grains in sunbird visited flowers of
Etlingera spp. For Heliconia spp. this experiment was not successful and
pollen tubes were rarely observed, even in hand pollinated flowers, where
enough pollen was deposited. The analyses of contacts with plant
reproductive organs nevertheless confirmed that sunbirds are good pollen
vectors for both Heliconia and Etlingera species. 4. Our study
demonstrated a high ecological fit between actors of distinct evolutionary
history and the general validity of bird-pollination syndrome. We moreover
show that trait matching and niche differentiation are important
ecological processes also in semi-artificial plant-pollinator systems.