A phylogenetic perspective on ecological specialisation reveals hummingbird and insect pollinators have generalist diets

Abstract

Specialisation in food resource use is a crucial process that fosters species coexistence in plant–animal networks, contributing to the maintenance of biodiversity, ecological complexity, and community stability. Notably, although there is a vast literature on ecological specialisation in pollination systems, the evolutionary similarity among the plant species visited by particular pollinators has been largely ignored. Here, we apply a robust phylogenetic approach to analyse whether the evolutionary relatedness of plant species is a significant factor in mediating pollinator visits and how it relates to the morphology of interacting species. We quantified ecological and clade specialisation of hummingbird and insect species in three mutualistic networks from the Costa Rican highlands and associated these metrics with species traits. We found that hummingbirds were overall ecologically more specialised than insects (i.e. visited a less diverse set of plant species). However, when evaluating the phylogenetic relatedness among the visited plant species, all hummingbird species and most insects had overdispersed diets, which indicates they visited phylogenetically distant plant species in the community. Moreover, a great proportion of these clade generalists visited plant species with a great variation in corolla length, showing a lack of preference for this morphological trait. Altogether, our results demonstrate that by incorporating plant phylogeny to network analysis, pollinator species were generalists and that corolla length weakly influences plant–pollinator interactions in the three studied networks. A phylogenetic perspective should occupy a central role in the study of specialisation since it contributes to understanding the interplay between ecological and evolutionary processes in mutualistic networks. Future research should focus on evaluating whether the phylogenetic structure of animal diets mediates patterns of interactions in different types of mutualisms and environmental contexts, linking these patterns to other floral traits. This knowledge may be valuable for deepening our comprehension of the underlying mechanisms shaping ecological networks.