Global patterns of interaction specialization in bird–flower networks
Authors: Zanata Thais B. , Dalsgaard Bo , Passos Fernando C. , Cotton Peter A. , Roper James J. , Maruyama Pietro K. , Fischer Erich , Schleuning Matthias , Martín González Ana M. , Vizentin‐Bugoni Jeferson , Franklin Donald C. , Abrahamczyk Stefan , Alárcon Ruben , Araujo Andréa C. , Araújo Francielle P. , Azevedo‐Junior Severino M. de. , Baquero Andrea C. , Böhning‐Gaese Katrin , Carstensen Daniel W. , Chupil Henrique , Coelho Aline G. , Faria Rogério R. , Hořák David , Ingversen Tanja T. , Janeček Štěpán , Kohler Glauco , Lara Carlos , Las‐Casas Flor M. G. , Lopes Ariadna V. , Machado Adriana O. , Machado Caio G. , Machado Isabel C. , Maglianesi María A. , Malucelli Tiago S. , Mohd‐Azlan Jayasilan , Moura Alan C. , Oliveira Genilda M. , Oliveira Paulo E. , Ornelas Juan Francisco , Riegert Jan , Rodrigues Licléia C. , Rosero‐Lasprilla Liliana , Rui Ana M. , Sazima Marlies , Schmid Baptiste , Sedláček Ondřej , Timmermann Allan , Vollstädt Maximilian G. R. , Wang Zhiheng , Watts Stella , Rahbek Carsten , Varassin Isabela G. 
Published: June 2017

Aim

Among the world's three major nectar‐feeding bird taxa, hummingbirds are the most phenotypically specialized for nectarivory, followed by sunbirds, while the honeyeaters are the least phenotypically specialized taxa. We tested whether this phenotypic specialization gradient is also found in the interaction patterns with their floral resources.

Location

Americas, Africa, Asia and Oceania/Australia.

Methods

We compiled interaction networks between birds and floral resources for 79 hummingbird, nine sunbird and 33 honeyeater communities. Interaction specialization was quantified through connectance (C), complementary specialization (H2′), binary (QB) and weighted modularity (Q), with both observed and null‐model corrected values. We compared interaction specialization among the three types of bird–flower communities, both independently and while controlling for potential confounding variables, such as plant species richness, asymmetry, latitude, insularity, topography, sampling methods and intensity.

Results

Hummingbird–flower networks were more specialized than honeyeater–flower networks. Specifically, hummingbird–flower networks had a lower proportion of realized interactions (lower C), decreased niche overlap (greater H2′) and greater modularity (greater QB). However, we found no significant differences between hummingbird– and sunbird–flower networks, nor between sunbird– and honeyeater–flower networks.

Main conclusions

As expected, hummingbirds and their floral resources have greater interaction specialization than honeyeaters, possibly because of greater phenotypic specialization and greater floral resource richness in the New World. Interaction specialization in sunbird–flower communities was similar to both hummingbird–flower and honeyeater–flower communities. This may either be due to the relatively small number of sunbird–flower networks available, or because sunbird–flower communities share features of both hummingbird–flower communities (specialized floral shapes) and honeyeater–flower communities (fewer floral resources). These results suggest a link between interaction specialization and both phenotypic specialization and floral resource richness within bird–flower communities at a global scale.