Diversifying agroecological systems: Plant-pollinator network organisation and landscape heterogeneity matter

Abstract

Agroecology is a process-based agriculture that implements agrobiodiversification to stabilize ecosystem processes and crop yield, leading to sustainable food systems. Traditionally, agrobiodiversification focused on increasing within-farm plant richness, which may increase local species richness of higher trophic levels. However, it is increasingly recognized that stabilizing ecosystem processes involving plant-animal interactions –e.g., pollination- requires practices that consider the organisation of interactions and heterogeneity effects at landscape level. In this work, we investigated how plant-pollinator interactions organised in agricultural landscapes harbouring agroecological farms and how landscape heterogeneity modulated interactions organisation. We characterized the organisation of 36 plant-pollinator networks describing interactions in nine agricultural landscapes -i.e., agroecological farms and their surroundings- across four flowering peak periods in the Agri-food region of central Córdoba, Argentina. We evaluated (1) centrality to network organisation of plant and pollinator only registered interacting in agroecological farms, farm surroundings (unique species) or in both locations (shared species); and (2) network organisation across gradients of landscape configurational (mean edge density) and compositional (forest proportion) heterogeneity. We found that plant-pollinator networks at landscape scale showed nested structures. Shared plant and pollinator species were the less represented in such networks but were central to networks organisation, i.e., they were connected to most species and with the highest frequency. Results also showed that network organisation changed with landscape configurational heterogeneity. Higher landscape mean edge density was associated with higher total and unique plant richness in networks and lower richness of shared plants. Network connectance and nestedness decreased with higher landscape mean edge density, i.e., plant and pollinator species interacted with less species, shared less interaction partners with more specialist species and showed lower interaction frequency with generalist partners in more heterogeneous landscapes. Our study showed that in agricultural landscapes harbouring agroecological farms (1) a few species inhabiting and showing interactions in both agroecological farms and their surroundings are key to the organisation of plant-pollinator interactions, and (2) landscape heterogeneity modulates such organisation. As interaction networks dynamic is influenced by network organisation, landscape configurational heterogeneity may modulate the stability of the pollination process and ultimately agroecological production. Thus, the agrobiodiversification of agroecological systems may benefit from considering the complexity of plant-pollinator interdependencies across agricultural landscapes and the effects of landscape heterogeneity on such complexity.