Abstract
Mutualistic interactions are powerful drivers of biodiversity on Earth that can be represented as complex interaction networks that vary in connection pattern and intensity. One of the most fascinating mutualisms is the interaction between hummingbirds and the plants they visit. We conducted an exhaustive search for articles, theses, reports, and personal communications with researchers (unpublished data) documenting hummingbird visits to flowers of nectar-rewarding plants. Based on information gathered from 4532 interactions between 292 hummingbird species and 1287 plant species, we built an interaction network between nine hummingbird clades and 100 plant families used by hummingbirds as nectar resources at a continental scale. We explored the network architecture, including phylogenetic, morphological, biogeographical, and distributional information. As expected, the network between hummingbirds and their nectar plants was heterogeneous and nested, but not modular. When we incorporated ecological and historical information in the network nodes, we found a generalization gradient in hummingbird morphology and interaction patterns. The hummingbird clades that most recently diversified in North America acted as generalist nodes and visited flowers with ornithophilous, intermediate and non-ornithophilous morphologies, connecting a high diversity of plant families. This pattern was favored by intermediate morphologies (bill, wing, and body size) and by the low niche conservatism in these clades compared to the oldest clades that diversified in South America. Our work is the first effort exploring the hummingbird-plant mutualistic network at a continental scale using hummingbird clades and plant families as nodes, offering an alternative approach to exploring the ecological and evolutionary factors that explain plant-animal interactions at a large scale.
Highlights
Mutualisms, such as seed dispersal and pollination, are key factors explaining the distribution and persistence of biodiversity on Earth [1]
The plant families with most species used by hummingbirds were Fabaceae (121 species), Bromeliaceae (81), Rubiaceae (70), Lamiaceae (69), Gesneriaceae (54), Ericaceae (51), Acanthaceae (51), Asteraceae (45), Malvaceae (37), and Bignoniaceae (35) (S1 Table)
The binary matrix with only native plant species included all the nine hummingbird clades, which interacted with 100 plant families through 385 links
Summary
Mutualisms, such as seed dispersal and pollination, are key factors explaining the distribution and persistence of biodiversity on Earth [1]. Mutualisms create complex networks of interacting species whose relationships vary in type, strength, and duration [2, 3]. The properties of the resulting interaction networks can help to describe and explain current biodiversity patterns [3]. Hummingbirds diversified into nine clades, some of which had a rapid rate of species diversification as a result of adaptation to new ecological niches and dispersion to new geographical areas [9]. Hummingbirds morphology and ecology (including relationships with flowers) reflect phylogeny, and hummingbird clades have characteristic morphologies that influence resource use, flight capabilities, competitive skills and environmental filtering, important mechanisms structuring hummingbird communities (Fig 1) [10, 11]
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