Disentangling the complexity of plant-bird relationships: From monolayer to multilayer network perspectives

Most plant-bird interaction research employing complex ecological networks focuses on pollination and seed dispersal interactions. However, birds and plants are immersed in a great variety and complexity of direct and indirect relationships. Therefore, the use of multilayer networks (i.e., species interaction networks involving different types of interactions) could provide new insights into the ecological and coevolutionary dynamics of plant-bird relationships. Here, we used a multilayer network approach to determine how a bird-plant interaction network involving different types of interactions (i.e., foraging for invertebrates on plants, frugivory, nectarivory, and perching) is organized in a peri-urban Mexican cloud forest. Moreover, we added information about the interactive roles of the winter migratory and resident birds in the multilayer network. In general, we found that the bird-plant multilayer network exhibits modular but a non-nested structure. We also observed that interactions involving perching and foraging for invertebrates on plants are more frequent than frugivory and nectarivory. Moreover, just a small proportion of birds and plant species were important to the network organization and for connecting different interaction types. In this case, we observed that only two bird species, Cardellina pusilla (Parulidae) and Dumetella carolinesis (Mimidae), and the plant species Telanthophora grandifolia (Asteraceae) and Platanus mexicanus (Platanaceae) presented higher centrality values (i.e., an interactive role). Finally, we found that betweenness values (i.e., the number of times a species acts as a bridge along the shortest path between two species) and network structure's contributions are similar for both migratory and resident bird species. Our results highlight the importance of key interacting species that connect other interacting species for the preservation of community cohesion and to the persistence of species-rich assemblages.