The influence of biogeographical and evolutionary histories on morphological trait‐matching and resource specialization in mutualistic hummingbird–plant networks
Authors: Dalsgaard Bo , Maruyama Pietro Kiyoshi , Sonne Jesper , Hansen Katrine , Zanata Thais B. , Abrahamczyk Stefan , Alarcón Ruben , Araujo Andréa C. , Araújo Francielle P. , Buzato Silvana , Chávez‐González Edgar , Coelho Aline G. , Cotton Peter A. , Díaz‐Valenzuela Román , Dufke Maria F. , Enríquez Paula L. , Martins Dias Filho Manoel , Fischer Erich , Kohler Glauco , Lara Carlos , Las‐Casas Flor Maria G. , Rosero Lasprilla Liliana , Machado Adriana O. , Machado Caio G. , Maglianesi María A. , Malucelli Tiago S. , Marín‐Gómez Oscar H. , Martínez‐García Vanessa , Mendes de Azevedo‐Júnior Severino , da Silva Neto Edvaldo Nunes , Oliveira Paulo E. , Ornelas Juan Francisco , Ortiz‐Pulido Raul , Partida‐Lara Ruth , Patiño‐González Blanca Itzel , Najara de Pinho Queiroz Steffani , Ramírez‐Burbano Mónica B. , Rodrigo Rech André , Rocca Márcia A. , Rodrigues Licléia C. , Rui Ana M. , Sazima Ivan , Sazima Marlies , Simmons Benno I. , Tinoco Boris A. , Varassin Isabela G. , Vasconcelos Marcelo F. , Vizentin‐Bugoni Jeferson , Watts Stella , Kennedy Jonathan D. , Rahbek Carsten , Schleuning Matthias , Martín González Ana M. 
Published: March 2021

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.

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