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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 m a.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.

A major challenge in evolutionary ecology is to understand how co-evolutionary processes shape patterns of interactions between species at community level. Pollination of flowers with long corolla tubes by long-tongued hawkmoths has been invoked as a showcase model of co-evolution. Recently, optimal foraging models have predicted that there might be a close association between mouthparts' length and the corolla depth of the visited flowers, thus favouring trait convergence and specialization at community level. Here, we assessed whether hawkmoths more frequently pollinate plants with floral tube lengths similar to their proboscis lengths (morphological match hypothesis) against abundance-based processes (neutral hypothesis) and ecological trait mismatches constraints (forbidden links hypothesis), and how these processes structure hawkmoth-plant mutualistic networks from five communities in four biogeographical regions of South America. We found convergence in morphological traits across the five communities and that the distribution of morphological differences between hawkmoths and plants is consistent with expectations under the morphological match hypothesis in three of the five communities. In the two remaining communities, which are ecotones between two distinct biogeographical areas, interactions are better predicted by the neutral hypothesis. Our findings are consistent with the idea that diffuse co-evolution drives the evolution of extremely long proboscises and flower tubes, and highlight the importance of morphological traits, beyond the forbidden links hypothesis, in structuring interactions between mutualistic partners, revealing that the role of niche-based processes can be much more complex than previously known.

The influence of floral resource availability on behaviour and dominance hierarchy of hummingbirds has seldom been investigated in open tropical environments. We evaluated the behavioural changes of hummingbirds associated with Palicourea rigida, a shrub common in the Cerrado, the open savanna areas in Central Brazil. We observed the foraging behaviour as a function of resource availability and experimentally manipulated floral display and nectar in order to define resource thresholds associated with territorial behaviour and territory intruding behaviour. Territorial behaviour was observed only in patches with high floral abundance and was restricted to some hummingbird species. The large Eupetomena macroura seems to be the dominant species in the community, excluding other hummingbirds and holding the richest patches. The experimental reduction in the floral abundance and nectar led to the abandonment of territory by these hummingbirds, which reinforces the idea that a certain threshold is necessary to maintain territorial defence. Higher floral display, on the other hand, seems to lead to higher frequency of intrusions and higher behavioural complexity of territory defenders, possibly meaning greater energy expenditure. The flower number and nectar manipulation affected visitation rates of territorial hummingbirds, but the frequency of intruders was affected only by the former manipulation. This indicates that territorial intruder use visual cues (floral abundance) as indicators of resource availability in order to estimate cost-benefit of territory invasion. Although territorial behaviour could limit pollen flow in patches with larger floral displays, this may be compensated by the territory invaders, which bring pollen from other patches. Zusammenfassung Der Einfluss von Ressourcenverfügbarkeit von Blüten auf das Verhalten und die Dominanzhierarchie von Kolibris in offenen, tropischen Landschaften ist bisher nur selten untersucht worden. Wir erfassten Verhaltensveränderungen von Kolibris in Assoziation mit Palicourea rigida, einem häufiger Strauch in der Cerrado, der offenen Baumsavanne in Zentralbrasilien. Wir untersuchten das Foragierverhalten als eine Funktion der Ressourcenverfügbarkeit. Dazu manipulierten wir Blüten-und Nektarverfügbarkeit experimentell um Schwellenwerte von Ressourcenverfügbarkeit, assoziiert mit Territorialverhalten, zu schätzen. Territorialverhalten wurde nur an Stellen mit hoher Blütenabundanz beobachtet, und war beschränkt auf nur einige Kolibriarten. Der große Eupetomena macroura scheint die dominante Art in der Gemeinschaft zu sein: diese Art schloss andere Kolibriarten aus und besetzte die reichsten Stellen. Die experimentelle Verringerung von Blüten-und Nektarverfügbarkeit führte zum Verlassen von Territorien durch diese Kolibris, welches die Idee eines Schwellenwertes, für die Entstehung von Territorialverhalten unterstützt. Vermehrte Blü-tenverfügbarkeit jedoch führte scheinbar zu einer höheren Frequenz von Intrusions, und zu höherer Komplexität des Verhaltens des Verteidiger...

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