Global patterns of interaction specialization in bird– flower networks
2017
Aim Among the world's three major nectar-feeding bird taxa,
hummingbirdsare the most phenotypically specialized for nectarivory, followed by
sunbirds, while the
honeyeatersare 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
sunbirdand 33
honeyeatercommunities. Interaction specialization was quantified through connectance (C), complementary specialization (H2′), binary (QB) and weighted modularity (Q), with both observed and
null-modelcorrected 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,
hummingbirdsand 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.
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