The distributions of morphologically specialized hummingbirds coincide with floral trait matching across an Andean elevational gradient

Abstract

Morphological trait matching between species affects resource partitioning in mutualistic systems. Yet, the determinants of spatial variation in trait matching remain largely unaddressed. Here, we generate a hypothesis that is based on the geographical distributions of species morphologies. To illustrate our hypothesis, as a study system we use hummingbirds in the tropical Andes. Hummingbirds with specialized morphologies (i.e., long or curved bills) may forage on flowers that are inaccessible to hummingbirds with generalized bill morphologies (i.e., small-to-medium-sized bills with no curvature), yet the vast majority of hummingbirds have generalized bill morphologies. Thus, we propose that trait matching across space is determined by the distribution of morphological specialists. In the Andes, we observe the richness of specialized hummingbird morphotypes to peak at high and low elevations. Therefore, we hypothesize that trait matching should be most influential in predicting pairwise interactions at high and low elevations. We illustrate our hypothesis by field observations along an elevational gradient in Podocarpus National Park (Ecuador). Using Bayesian hierarchical modeling of interaction frequencies in combination with network analyzes, we found that hummingbirds at high and low elevations contributed to resource partitioning by foraging on morphologically close-matching flowers.Moreover, at high and low elevations, hummingbirds with specialized morphologies showed a stronger tendency to visit close-matching flowers than morphological nonspecialists did. In contrast, at mid-elevations, hummingbirds were not attracted to morphologically close-matching flowers. These results suggest that the spatial distribution of specialized morphotypes determines trait matching and the partitioning of interactions within hummingbird-plant communities.Abstract in Spanish is available with online material. K E Y W O R D SEcuador, modularity, mutualism, networks, plants, Podocarpus National Park, pollination, resource partitioning, specialization 206 | SONNE Et al.

Forbidden links, trait matching and modularity in plant-hummingbird networks: Are specialized modules characterized by higher phenotypic floral integration?

“…However, plant-hummingbird mutualistic networks are considered a specialized system, particularly those located near the Equator due to higher productivity and the relatively stable and predictable availability of resources throughout the year ( Feinsinger & Colwell, 1978 ; Dalsgaard et al, 2011 ; Belmaker, Sekercioglu & Jetz, 2012 ; Zanata et al, 2017 ). Hence, several studies have shown that mismatches in species morphology and phenology play a major role in structuring interactions in plant-hummingbird systems ( Stiles, 1975 , 1978 ; Lara, 2006 ; Maglianesi et al, 2014 ; Maruyama et al, 2014 ; Vizentin-Bugoni, Maruyama & Sazima, 2014 ; Sonne et al, 2019 ). Hummingbird clades have characteristic morphologies that influence resource use, flight capabilities, competitive skills and environmental filtering, important mechanisms structuring hummingbird communities ( Rodríguez-Flores et al, 2019 ).…”

A geographical perspective on the relationship between Impatiens spur lengths and bill lengths of sunbirds in Afrotropical mountains

“…This suggests evidence for trait matching between taxa involved in pollination/nectarivory interactions at assemblage level and over a large spatial scale in tropical Africa, which has been never shown before. The geographical variation in trait-matching generally remains poorly explicitly investigated, even though Sonne et al (2019) recently showed that the traitmatching within hummingbird-plant communities is influenced by spatial distribution of morphotypes. In our study, we showed that TA B L E 1 The correlations between Impatiens spur lengths and bill lengths of sunbirds in individual communities performed the analyses for forest and nonforest sunbird species separately.…”

“…The geographical variation in trait‐matching generally remains poorly explicitly investigated, even though Sonne et al. (2019) recently showed that the trait‐matching within hummingbird–plant communities is influenced by spatial distribution of morphotypes. In our study, we showed that geographical space use of involved taxa determined by habitat selection contributes to the observed trait matching.…”

Population‐level plant pollination mode is influenced by Quaternary climate and pollinators

“…In general, there is less pollen limitation when the pollination systems are more generalized, exhibiting a higher probability of pollen being transferred to conspecific stigmas (Knight et al., 2005; Lopes et al. submittted ). Generalized pollination systems are therefore more resistant to pollinator species loss, and, hence, they are hypothesized to predominate in environments where the pollinator fauna is highly variable (Waser et al., 1996) or not immediately fitted to the ancestral pollination mode, such as on islands (Armbruster & Baldwin, 1998; Rivera‐Marchand & Ackerman, 2006; Sonne et al., 2019). More diverse sets of pollinators can also be functionally more stable over time and space due to the buffering effect of different species responding in different ways to environmental changes, that is, the “biodiversity insurance hypothesis” (Bartomeus et al., 2013; Loreau, 2001).…”