Morphological traits determine specialization and resource use in plant–hummingbird networks in the neotropics

Abstract

Ecological communities are organized in complex ecological networks. Trait‐based analyses of the structure of these networks in highly diversified species assemblages are crucial for improving our understanding of the ecological and evolutionary processes causing specialization in mutualistic networks. In this study, we assessed the importance of morphological traits for structuring plant–hummingbird networks in Neotropical forests by using a novel combination of quantitative analytical approaches. We recorded the visitation of hummingbirds to plant species over an entire year at three different elevations in Costa Rica and constructed quantitative networks based on interaction frequencies. Three morphological traits were measured in hummingbirds (bill length, bill curvature, and body mass) and plants (corolla length, curvature, and volume). We tested the effects of avian morphological traits and abundance on ecological specialization of hummingbird species. All three morphological traits of hummingbirds were positively associated with ecological specialization, especially bill curvature. We tested whether interaction strength in the networks was associated with the degree of trait matching between corresponding pairs of morphological traits in plant and hummingbird species and explore whether this was related to resource handling times by hummingbird species. We found strong and significant associations between interaction strength and the degree of trait matching. Moreover, the degree of trait matching, particularly between bill and corolla length, was associated with the handling time of nectar resources by hummingbirds. Our findings show that bill morphology structures tropical plant–hummingbird networks and patterns of interactions are closely associated with morphological matches between plant and bird species and the efficiency of hummingbirds' resource use. These results are consistent with the findings of seminal studies in plant–hummingbird systems from the neotropics. We conclude that trait‐based analyses of quantitative networks contribute to a better mechanistic understanding of the causes of specialization in ecological networks and could be valuable for studying processes of complementary trait evolution in highly diversified species assemblages.

Morphology predicts species' functional roles and their degree of specialization in plant–frugivore interactions

“…This corroborates that trait matching in species from different trophic levels strongly influences whether or not species interact [1,3,5,6]. In addition, our results show that morphological matching on the scale of individual interactions leads to an overall congruency in the trait spaces of interacting species groups.…”

Process-Based Species Pools Reveal the Hidden Signature of Biotic Interactions Amid the Influence of Temperature Filtering

“…High-altitude hummingbirds are characterized by short and straight beaks (e.g., Chalcostigma, Metallura, Ramphomicron, Eriocnemis, Oxypogon, Aglaeactis), and the variation and range of beak lengths is narrower at high than at low elevations (data not shown), possibly reflecting an environmental filter related to coevolution with flowers (Wolf et al 1976;Brown and Bowers 1985;Maglianesi et al 2014). One possible explanation for the lack of consistency among patterns of phylogenetic and trait assemblage structure is that it may merely be a statistical artifact of having less power at high elevations to detect a significant deviation.…”

“…In hummingbirds, the extreme metabolic demands of hovering flight lead to intense exploitative and interference competition for floral nectar resources (Feinsinger and Colwell 1978;Feinsinger et al 1979;Altshuler and Dudley 2002). In addition, hummingbirds partition resources through differences in beak morphology (Feinsinger and Colwell 1978;Maglianesi et al 2014;Vizentin-Bugoni et al 2014). However, the signature of niche differentiation might emerge only after accounting for the influence of environmental filters.…”

“…Specifically, since temperature explains much variation in hummingbird assemblage structure (Graham et al 2009, we predicted that a temperaturebased species pool would have the strongest influence on the perceived structure of hummingbird communities. Concordantly, we hypothesized that (2) patterns of beak length dispersion, which might reflect competition for food resources (Stiles 2008;Graham et al 2012;Maglianesi et al 2014), would be evenly dispersed and that this pattern would become stronger after accounting for temperature filtering. Finally, we hypothesized that (3) patterns of body mass dispersion, a trait that is under strong selection pressure in cold Andean environments (Brown and Bowers 1985;Stiles 2008;Graham et al 2012), would appear clustered when using a broadly defined species pool but random when using a species pool that accounts for temperature filtering.…”

Phylogenetic and Functional Diversity of Fleshy-Fruited Plants Are Positively Associated with Seedling Diversity in a Tropical Montane Forest

“…In turn, the foraging behavior of mutualistic animals influences plant demography at the community level (Yang et al, 2008). Plantanimal interactions are mediated by morphological traits, i.e., physically measurable properties of individuals, that modify the intensity of interactions across trophic levels (Bello et al, 2010;Maglianesi et al, 2014). Therefore, trait variation among the plant species involved in the interactions affects ecological processes and ecosystem functioning (Díaz and Cabido, 2001).…”