Functional diversity mediates macroecological variation in plant–hummingbird interaction networks

Abstract

Aim Species interaction networks are known to vary in structure over large spatial scales. We investigated the hypothesis that environmental factors affect interaction network structure by influencing the functional diversity of ecological communities. Notably, we expect more functionally diverse communities to form interaction networks with a higher degree of niche partitioning. Location: Americas. Time period: Current. Major taxa studied: Hummingbirds and their nectar plants. Methods We used a large dataset comprising 74 quantitative plant–hummingbird interaction networks distributed across the Americas, along with morphological trait data for 158 hummingbird species. First, we used a model selection approach to evaluate associations between the environment (climate, topography and insularity), species richness and hummingbird functional diversity as predictors of network structure (niche partitioning, i.e., complementary specialization and modularity). Second, we used structural equation models (SEMs) to ask whether environmental predictors and species richness affect network structure directly and/or indirectly through their influence on hummingbird functional diversity. For a subset of 28 networks, we additionally evaluated whether plant functional diversity was associated with hummingbird functional diversity and network structure. Results Precipitation, insularity and plant richness, together with hummingbird functional diversity (specifically, functional dispersion), were consistently strong predictors of niche partitioning in plant–hummingbird networks. Moreover, SEMs showed that environmental predictors and plant richness affected network structure both directly and indirectly through their effects on hummingbird functional diversity. Plant functional diversity, however, was unrelated to hummingbird functional diversity and network structure. Main conclusions: We reveal the importance of hummingbird functional diversity for niche partitioning in plant–hummingbird interaction networks. The lack of support for similar effects for plant functional diversity potentially indicates that consumer functional diversity might be more important for structuring interaction networks than resource functional diversity. Changes in pollinator functional diversity are therefore likely to alter the structure of interaction networks and associated ecosystem functions.

The geographical variation of network structure is scale dependent: understanding the biotic specialization of host–parasitoid networks

“…Further analyses using finer measures that consider climatic fluctuations in the past might unveil different effects on biotic specialization. Similarly, other environmental variables, such as precipitation, have been related to the geographical variation of network nestedness (Sebastián-González et al 2015), modularity (Trøjelsgaard and Olesen 2013, Sebastián-González et al 2015), or to the biotic specialization of plant-hummingbird communities (Dalsgaard et al 2011, Maruyama et al 2018). However, our aim was to evaluate the effect of climatic constancy on biotic specialization and, therefore, precipitation was not included in the analyses given that it is not directly related to a region’s climatic constancy.…”

Abundance drives broad patterns of generalisation in plant–hummingbird pollination networks

“…Here we evaluate the direction of the abundance-generalisation relationship in plant-hummingbird pollination networks and use a null model to assess the extent to which observed patterns of species-level generalisation can be explained by neutral effects. Plant-hummingbird interactions are a particularly interesting model system to answer these questions as they involve species spanning the entire specialisation-generalisation spectrum (Bleiweiss 1998, Martín González et al 2015, Dalsgaard et al 2018, Maruyama et al 2018. Additionally, pollination by vertebrates is important, especially in the tropics (Bawa 1990, Vizentin-Bugoni et al 2018, and is on average responsible for 63% of fruit or seed production in vertebrate-pollinated plants (Ratto et al 2018).…”

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

“…The partitioning of resources among species within ecological communities has implications for co‐existence and may thereby affect geographical patterns in species richness (Dobzhansky, ; Michalet et al., ; Schemske, ). Resource partitioning among species having different morphological traits is thought to enable them to specialize on resources that are inaccessible or energetically less favorable to competitors (Dehling, Jordano, Schaefer, Böhning‐Gaese & Schleuning, ; Grant & Grant, ; Maruyama et al., ; Stang, Klinkhamer & Van Der Meijden, ; Temeles & Kress, ). For instance, within mutualistic systems, such as flowering plants and their pollinators, morphological co‐adaptations may result in plants having floral corolla shapes matching the feeding apparatus of their most effective animal pollinators (e.g., Darwin, ; Rothschild, ; Temeles & Kress, ).…”