The influence of biogeographical and evolutionary histories on morphological trait‐matching and resource specialization in mutualistic hummingbird–plant networks

Abstract

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.

Testing for pollinator recognition in multiple species of Heliconia

“…In Peru, seven hummingbird species of various sizes and with various bill shapes have been observed visiting H. rostrata , but nothing is known of their pollination efficiencies [38]. Based on our results showing increased pollen tube rates in bird-visited flowers compared to hand pollination, we posit that H. rostrata could filter visits from animals without complementary morphologies, such as insects.…”

“…In Peru, seven hummingbird species of various sizes and with various bill shapes have been observed visiting H. rostrata, but nothing is known of their pollination efficiencies [53].…”

Synergism, Bifunctionality, and the Evolution of a Gradual Sensory Trade-off in Hummingbird Taste Receptors

“…The substantial variation in response profiles of different hummingbird taste receptors both to carbohydrates as well as to amino acids underscores a key role for taste ( Gardener and Gillman 2002 ) (in addition to the better-understood traits of color, [Stiles 1976 ] and corolla morphology, [Temeles et al 2009 ]) in the coevolution between hummingbirds and plants ( Dalsgaard et al 2021 ). The unexpected discovery of synergistic responses broadens our understanding of how T1R taste receptors function and opens a new ecological angle for future research.…”

Tropical hummingbird pollination networks are resistant to short-term experimental removal of a common flowering plant

“…Analyses of radio telemetry data (i.e., proportion of time spent in focal area) included a covariate for the focal area size. When analyzing visitation rates of Heliconia specialists to non- Heliconia resources, we also included plant corolla length as a covariate, since these relatively long-billed hummingbirds (mean bill lengths of 40 and 33 mm: Borgella, Snow, and Gavin 2001) are expected to select plant species with long corolla tubes (e.g., Maglianesi et al 2014; Vizentin-Bugoni, Maruyama, and Sazima 2014; Dalsgaard et al 2021). We included random effects for Site in all models; additional random effects were included where applicable (Appendix S2: Table S18).…”