Impacts of landscape heterogeneity on bottom-up effects affecting biological control

Conservation biological control of crop pests by natural enemies relies on management strategies to favour their trophic interactions. In agricultural landscapes, natural enemies acting across habitat boundaries may feed on non-pest prey, resulting in apparent competition between non-pest prey and pests. Such communities, including pests, non-pest prey, and natural enemies have been shown to be affected by landscape heterogeneity depending on the dispersal capacity of the interacting organisms. Nonetheless, a mechanistic understanding of how natural enemies' dispersal capacity interacts with landscape heterogeneity affecting conservation biological control is, however, lacking. Here, we contribute to such mechanistic understanding through modelling. We simulated the consequences of differences in landscape heterogeneity defined by the contrast of plant resource distribution in a semi-natural habitat compared to a crop and variation in natural enemy dispersal capacity on biological control of a pest. Our model showed that variation in plant resource distribution resulted in bottom-up effects that led to shifts in the dominant mechanism underlying biological control. At high landscape heterogeneity when resources differ strongly between crop and the semi-natural habitat, non-pest prey benefitted from the plant resources available, promoting apparent-competition-mediated biocontrol for high-dispersing natural enemies. At low landscape heterogeneity, pests benefitted mostly from plant resources available, promoting direct plant-pestenemy mediated biocontrol. Interestingly, intermediate levels of landscape heterogeneity resulted in the lowest levels of biocontrol. Our results highlight the importance of potential bottom-up effects that the matching between plant resources available in a habitat and the resource preference of herbivores can induce on conservation biological control.