Ecological Interactions between Plants and Hummingbirds in a Successional Tropical Community

Abstract

At Monteverde, Costa Rica, 10 successional plant species used 14 hummingbird species for pollination. Displacement among flowering seasons suggests that the plants influenced hummingbirds to abandon another. There was no evidence that the flowering of one plant influenced hummingbirds to abandon another Pollination is simultaneously flowering plants likely suffered nonetheless, since birds tended to move indiscriminately among flowers of different species and could lose much pollen between successive visits to conspecific plants. This may have led to scatter in flowering peaks by favoring the quick establishment of plant colonists with unique flowering seasons over colonists whose flowering seasons coincided with those of established species. The continuous supply of nectar provided by staggered flowering peaks maintained a continuous supply of hummingbirds competing for nectar. Even inconspicuous plants with few flowers received sufficient hummingbird visits for moderate to high potential rates of outbreeding. At large, flower—laden trees and shrubs, hummingbirds defending feeding territories evidently effected much inbreeding, but movements of intruders between territories kept inbreeding from becoming absolute. Nectar secretion rates varied widely among flowers of each of the 5 plant species in which nectar volume was measured. Many flowers produced little or no nectar, while a few secreted quite copious volumes. This "bonanza" pattern may benefit plants by reducing caloric expenditures on nectar while increasing the duration of hummingbirds' foraging bouts. The latter possibility was tested and verified experimentally with artificial flowers exposed to a free—living hummingbird on Trinidad, West Indies. When pollinators are abundant, plants with "bonanza" patterns can attract consistent visitors and rare, inconspicuous plants can count on consistent service. At Monteverde, the unspecialized, opportunistic nature of both plants and birds assured abundant hummingbirds and resulted in a well—integrated complex of plants and pollinators despite the transient nature of the successional habitats.