Functional structure and specialization in three tropical plant–hummingbird interaction networks across an elevational gradient in Costa Rica

Submitted by editor on 30 October 2015. Get the paper!


 By María Alejandra Maglianesi 

A primary aim of community ecology is to identify the processes that govern multispecies assemblages across environmental gradients. Ecological networks comprising interacting species of plants and pollinators are particularly suitable for testing effects of spatial environmental gradients on the functional structure and specialization in multispecies assemblages. However, at present there are few studies that link species functional traits with patterns of interactions in plant–pollinator networks, especially in the tropics. 

In this study, we investigated patterns in functional structure and specialization in plant–hummingbird mutualistic networks across elevations and the processes driving these patterns in three tropical forests of Costa Rica. We quantified different metrics of functional community structure based on three morphological traits (bill length, bill curvature and body mass) of hummingbird species at three elevations (Fig. 1). We used pollen carried by mist–netted hummingbird individuals to construct plant–hummingbird networks at the individual and species level at each elevation (Fig. 2). 

 Figure 1. Measuring morphological traits in hummingbirds: bill length, bill curvature and body mass (A, B and C, respectively). Photos by María Alejandra Maglianesi. 


Our results show consistent patterns in the functional structure of hummingbird assemblages and specialization of hummingbird species and individuals across elevations. Hummingbird assemblages varied from being functionally even and over–dispersed in the lower elevations to uneven and clustered in high–elevation environments. Accordingly, hummingbird species and individuals were more specialized at low and mid elevations than at the highest elevation. Spatial variation in competition and animal resource use at the species and individual level may be a crucial mechanism for shaping the functional structure of highly diversified species assemblages and may also be important for structuring spatial patterns in other types of ecological networks and multispecies assemblages. 

Figure 2. Plant–hummingbird interaction networks based on pollen analysis. Lampornis hemileucus visiting Renealmia cernua at the Braulio Carrillo National Park in Costa Rica (A). Collecting pollen loads from hummingbird (Lampornis calolaema) by using fuchsine–stained gelatine cubes (B) to later identify the pollen in the lab (C) and determine plant–hummingbird interactions (D). Photos by María Alejandra Maglianesi.