Data from: Floral isolation and pollination in two hummingbird-pollinated heliconias data

Differences in feeding performance and aggressive abilities between
species and sexes of hummingbirds are often associated with the
partitioning of their food sources, but whether such partitioning results
in floral isolation (reproductive isolation at the stage of pollination)
has received little attention. We examined components of floral isolation
and pollinator effectiveness of Heliconia caribaea and H. bihai on the
island of Dominica, West Indies. The short flowers of H. caribaea match
the short bills of male Anthracothorax jugularis, its primary pollinator,
whereas the long flowers of H. bihai match the long bills of female A.
jugularis, its primary pollinator. In pollination experiments, both sexes
of A. jugularis were equally effective at pollinating the short flowers of
H. caribaea, which they preferred to H. bihai, whereas females were more
effective at pollinating the long flowers of H. bihai. Moreover, an
average difference in length of 12 mm between H. caribaea and H. bihai
flowers did not prevent heterospecific pollen transfer, and both sexes
transported pollen between the two plant species. In field studies using
powdered dyes as pollen analogs, however, heterospecific pollen transfer
was minimal, with only 2 of 168 flowers receiving dye from the other
species. The length of H. bihai flowers acted as an exploitation barrier
to male A. jugularis, which were unable to completely remove nectar from
88% of the flowers they visited. In contrast, interference competition
combined with high floral fidelity through traplining prevented female A.
jugularis from transferring pollen between the two Heliconia species. A
combination of exploitation barriers, interference and exploitative
competition, and pollinator preferences maintains floral isolation between
these heliconias, and may have contributed to the evolution of this
hummingbird-plant system.