The most likely hummingbird population composition in an ecosystem where most flowers are long and bell-shaped would be:
more long-beaked hummingbirds.
This is because long-beaked hummingbirds would have better access to the nectar in the long, bell-shaped flowers, giving them a survival advantage. As a result, they would be more successful in feeding and reproducing in this environment compared to short-beaked hummingbirds.