Functional traits can determine pairwise species interactions, such as those between plants and pollinators. However, the effects of biogeography and evolutionary history on trait-matching and trait-mediated resource specialization remain poorly understood. We compiled a database of 93 mutualistic hummingbird–plant networks (including 181 hummingbird and 1,256 plant species), complemented by morphological measures of hummingbird bill and floral corolla length. We divided the hummingbirds into their principal clades and used knowledge on hummingbird biogeography to divide the networks into four biogeographical regions: Lowland South America, Andes, North & Central America, and the Caribbean islands. We then tested: (a) whether hummingbird clades and biogeographical regions differ in hummingbird bill length, corolla length of visited flowers and resource specialization, and (b) whether hummingbirds' bill length correlates with the corolla length of their food plants and with their level of resource specialization. Hummingbird clades dominated by long-billed species generally visited longer flowers and were the most exclusive in their resource use. Bill and corolla length and the degree of resource specialization were similar across mainland regions, but the Caribbean islands had shorter flowers and hummingbirds with more generalized interaction niches. Bill and corolla length correlated in all regions and most clades, that is, trait-matching was a recurrent phenomenon in hummingbird–plant associations. In contrast, bill length did not generally mediate resource specialization, as bill length was only weakly correlated with resource specialization within one hummingbird clade (Brilliants) and in the regions of Lowland South America and the Andes in which plants and hummingbirds have a long co-evolutionary history. Supplementary analyses including bill curvature confirmed that bill morphology (length and curvature) does not in general predict resource specialization. These results demonstrate how biogeographical and evolutionary histories can modulate the effects of functional traits on species interactions, and that traits better predict functional groups of interaction partners (i.e. trait-matching) than resource specialization. These findings reveal that functional traits have great potential, but also key limitations, as a tool for developing more mechanistic approaches in community ecology. A free Plain Language Summary can be found within the Supporting Information of this article.
Bibliografisk noteFunding Information:
B.D., K.H. and B.I.S. thank the Independent Research Fund Denmark for its support (grant no. 0135‐00333B). B.D., J.S., K.H., C.R. and A.M.M.G. thank the Danish National Research Foundation for its support of the Center for Macroecology, Evolution and Climate (grant no. DNRF96). J.S. and C.R. were supported by research grant no. 25925 from VILLUM FONDEN. This study was supported by CAPES (PDSE scholarship proc. 8105/2014‐6 to T.B.Z.; Finance Code 001 to T.B.Z., T.S.M. and J.V.‐B.; CNPq grant 445405/2014‐7 and PQ scholarship 313801/2017‐7 to I.G.V.). A.C.A. and E.F. thanks CAPES/FUNDECT PAPOS for the grant 23/200.638/2014, A.C.A. thanks CNPq for a PQ scholarship (310999/2018‐9) and E.F. thanks to CNPq researcher grant (306345/2019‐6). A.G.C., M.M.D.F. and E.N.N. also thanks the CAPES for funding. C.L. received financial support from ESDEPED‐UATx. C.G.M. was funded by FAPESB and CNPq. M.A.M. thank the Consejo Nacional para Investigaciones Científicas y Tecnológicas (CONICIT) and the research‐funding program ‘LOEWE‐Landes‐Offensive zur Entwicklung Wissenschaftlich‐ökonomischer Exzellenz' of Hesse's Ministry of Higher Education, Research, and the Arts. O.H.M.‐G. was supported by the National Council of Science and Technology (CONACYT 417094) and the Doctoral Program of the Instituto de Ecología, A.C.A. (INECOL). R.O.‐P. thanks CONACyt (project grant # 258364). M.B.R.‐B. thanks COLCIENCIAS for a Ph.D. scholarship (617‐2013), IDEA WILD for equipment donation, and Fundación ProAves and American Bird Conservancy for support to conduct fieldwork. A.R.R. and S.N.P.Q. thank CAPES (Financial code 001) for funding. I.S. and M.Sa. thank the National Council of Scientific and Technological Development ‐ CNPq grants 300992/79‐ZO and 302781/2016‐1, respectively; B.I.S. was supported by Royal Commission for the Exhibition of 1851 Research Fellowship. J.V.‐B. thank the US Army and CERL‐ERDC for funding, and S.W. thanks The British Ecological Society, The Biodiversity Trust and The Anglo Peruvian Society for grants. J.K. was supported by a Reintegration Fellowship from the Carlsberg Foundation (CF19‐0334). A.M.M.G. was supported through a Marie Skłodowska‐Curie Individual Fellowship (H2020‐MSCA‐IF‐2015‐704409).
© 2021 British Ecological Society