Competition and Coexistence in a Simple Tropical Community

Nectarivorous mites of the genus Rhinoseius breed and feed in hummingbird-pollinated flowers and are dispersed in the nasal cavities of hummingbirds. An analysis is presented of the evolutionary and ecological interactions among 10 species in a Costa Rican highland community: two Rhinoseius species, three hummingbirds, a coerebid bird, and four hummingbird-pollinated plants. Coexistence of two territorial hummingbirds at the study site is allowed by migration, sequential specialization on seasonal resources, and behavioral interactions. The third hummingbird is an interstitial species dependent on a variety of widely dispersed food plants. The coerebid bird, a nectar thief, feeds within hummingbird territories on relatively indefensible flowers. Coexistence of the two mite species, capable of lethal combat, depends upon the grain structure of their environment, which is determined by hummingbird feeding patterns. This is demonstrated by a probabilistic model based on field data. Tropical environments favor sequential specialists, interstitial species, grain specialists, and hypercontingent species. These adaptive strategies probably account in part for high tropical species diversity.