Origin of hummingbird faunas

Abstract

Ecological studies of hummingbird communities have emphasized the importance of local conditions and contemporary interactions in the development of these varied faunas. A time-calibrated, DNA hybridization-based phylogeny of the principal hummingbird lineages was used to examine historical aspects of hummingbird faunas in the species-rich tropical lowlands and Andes, and the relatively depauperate West Indies and temperate regions of Central and North America. Parsimony reconstructions of ancestral distributions indicate that these faunas are polyphyletic in origin, comprising several to many independent lineages. Based on the timing of geologic and cladogenic events, hummingbird faunas appear to have arisen more often by colonization than by large-scale vicariance, with multiple dispersals across water gaps, elevational gradients, and latitude. The extent to which particular lineages colonized different regions depended, however, on lineage ecology as well as on the habitat and age of the fauna. In general, the oldest extant trochilofauna, which today occupies the tropical lowlands, was the principal source of colonizing taxa. However, all regions except possibly the West Indies contributed taxa now found elsewhere, including in the tropical lowlands. The Andean fauna comprises several lineages with lowland origin (hermits, Mangoes, Brilliants, Coquettes, Emeralds) as well as at least one that arose in temperate regions outside South America (Bees). At least two lineages that colonized the West Indies gave rise to endemic genera (Mangoes toEulampis, and Emeralds toOrthorhyncus). Even groups that diversified in the highlands (Brilliants and Bees) gave rise to taxa that subsequently reinvaded the tropical lowlands. As the result of these varied histories, hummingbird communities cannot be arranged easily with respect to organizational complexity and coevolution with nectar sources. Although the physically insular faunas in the Andes and West Indies differ markedly in diversity, both were more strongly affected by colonization than the other faunas. A high potential for coevolution between hummingbirds and plants probably facilitated the successful establishment and radiation of the several Andean-associated lineages. However, coexistence between the two most diverse Andean clades may have been favoured initially through different habitat preferences by their extra-Andean ancestors. In the tropical lowlands, by comparison, the basic separation between the forest-dwelling hermits and canopy and edge-dwelling nonhermits appears to have evolved in situ. The low species and morphologic diversity of hummingbirds breeding north of Mexico reflects the predominance there of a single relatively recent lineage. The regional coexistence of numerous unrelated lineages implies that patterns of ancestry, colonization, and extinction contribute to the make-up of contemporary species-rich hummingbird faunas and serves to qualify the view that hummingbird communities are coadapted assemblages that resist change.