In an ecosystem where most flowers are long and bell-shaped, the most likely hummingbird population composition would be:
more long-beaked hummingbirds.
This is because long-beaked hummingbirds would be better adapted to access the nectar in the long, bell-shaped flowers, giving them an advantage in feeding and survival compared to short-beaked hummingbirds. As a result, you would expect to see a higher population of long-beaked hummingbirds over time.