Landscape structure influences modularity patterns in farm food webs: consequences for pest control

Landscape management affects species interactions within a community, leading to alterations in the structure of networks. Modules are link-dense regions of the network where species interact more closely within the module than between modules of the network. Insufficient network resolution has meant that modules have proved difficult to identify, even though they appear important in the propagation of disturbance impacts. We applied a standardized approach across 20 farms to obtain well-resolved food webs to characterize network structure and explore how modularity changes in response to management (organic and conventional). All networks showed significantly higher modularity than random networks. Farm management had no effect on the number of modules per farm or module richness, but there was a significant loss of links between modules on conventional farms, which may affect the long-term stability of these networks. We found a significant association between modules and major habitat groups. If modules form as a result of interactions between species that utilize similar habitats, then ecosystem services to the crop components of the landscape, such as pest control by parasitoids originating in the non-crop vegetation, are less likely to occur on these farms.