Local and landscape-level impacts of agricultural intensification on arthropod communities and their interaction networks

Arthropods play a central role in agricultural landscapes being responsible for the delivery of many ecosystem services such as pollination, biological pest control, and nutrient cycling. But the current global decline of arthropods is intensified by habitat modification, loss and fragmentation, pesticide use and other intensive management practices. Thus, it is crucial to understand how such impacts affect ecosystem services provisioning. In this thesis, I aim to explore how the management of local crop fields and landscape composition affect beneficial arthropod communities at different levels, including abundances and diversity of species and species interaction networks. I focus on predaceous and parasitic insects that provide biological pest control and pollinators. I assess i) how crop diversity affects arthropod diversity, ii) how fertilisation affects the local predator community and pest control, iii) how crop type (annual vs perennial) and landscape composition affect the predator-prey and host-parasitoid interaction networks and the implications for pest control. I found that increasing crop diversity in landscapes with a high proportion of seminatural habitats can enhance the diversity of beneficial arthropods. I also detected that organic fertilisation can benefit the abundance of local predators while specialist predators that move into the crop from the surrounding habitats boost biological pest control. I also found that crop type and landscape composition have effects beyond community species composition as also the interaction networks were altered, modifying the network stability and pest control potential. My findings suggest that the main drivers of change in agricultural landscapes affect arthropod communities at different levels. Effects of habitat type and local management can be observed not only in the community composition, but some of the consequences were also reflected in the species interaction networks. Finally, I show that food web ecology can link community composition and ecosystem service provisioning.