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| Aim To investigate the association between hummingbird–plant network structure
and species richness, phylogenetic signal on species’ interaction pattern, insularity
and historical and current climate.
Location Fifty-four communities along a c. 10,000 km latitudinal gradient across
the Americas (39° N–32° S), ranging from sea level to c. 3700 ma.s.l., located on the
mainland and on islands and covering a wide range of climate regimes.
Methods We measured the level of specialization and modularity in mutualistic
plant–hummingbird interaction networks. Using an ordinary least squares
multimodel approach, we examined the influence of species richness, phylogenetic
signal, insularity and current and historical climate conditions on network structure
(null-model-corrected specialization and modularity).
Results Phylogenetically related species, especially plants, showed a tendency
to interact with a similar array of mutualistic partners. The spatial variation
in network structure exhibited a constant association with species phylogeny
(R2 = 0.18–0.19); however, network structure showed the strongest association with
species richness and environmental factors (R2 = 0.20–0.44 and R2 = 0.32–0.45,
respectively). Specifically, higher levels of specialization and modularity were associated
with species-rich communities and communities in which closely related
hummingbirds visited distinct sets of flowering species. On the mainland, specialization
was also associated with warmer temperatures and greater historical temperature
stability.
Main conclusions Our results confirm the results of previous macroecological
studies of interaction networks which have highlighted the importance of species
richness and the environment in determining network structure. Additionally, for
the first time, we report an association between network structure and species
phylogenetic signal at a macroecological scale, indicating that high specialization
and modularity are associated with high interspecific competition among closely
related hummingbirds, subdividing the floral niche. This suggests a tighter
co-evolutionary association between hummingbirds and their plants than in previously
studied plant–bird mutualistic systems. | |
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