Common birds combine pest control and seed dispersal in apple orchards through a hybrid interaction network

Abstract

Farmland ecosystem services frequently result from different ecological functions simultaneous provided by specific biodiversity groups such as birds. These bundles of ecosystem services may be approached from inter-specific interaction networks, which inform about the structure of interactions while identifying the species more relevant for combining ecosystem services. Here, we studied how birds provide pest control in apple orchards, and seed dispersal in orchard-adjacent hedgerows and forests. For this, we used field data and DNA-metabarcoding of bird fecal samples, obtained across a whole year from three orchards in northern Spain, to build interaction networks between birds and arthropod apple pests, and between birds and non-crop fleshy-fruited plants. We addressed the structure of the different networks underpinning pest control and seed dispersal. We also combined both ecosystem services through a hybrid network to assess, by means of centrality measures, the topological roles of individual bird species and their ecological determinants. Interaction networks differed in structure, with pest-control network showing higher modularity and specialization than seed-dispersal network, otherwise characterized by high nestedness. These differences emerged from the different typologies, i.e. antagonistic vs. mutualistic, of the bird-pest and bird-plant interactions. The hybrid network integrating pest control and seed dispersal evidenced strong variability across birds in their role to connect ecosystem services, depending on their central or peripheral positions. Bird centrality was positively related with species abundance and independent of body size or diet diversity. This finding suggests the relevance of neutral processes (i.e. the random encounters of organisms) for driving inter-specific interactions, and it highlights the relevance of common birds for sustaining ecosystem service bundles in agroecosystems. The preservation of fruit-rich hedgerows and forest patches around apple orchards is an action recommended to maintain the populations of common bird species, responsible of both agricultural pest control and the natural regeneration of these habitats.