Emergent effects of ground beetles size diversity on the strength of prey suppression

1. Determining how multiple predators provide better prey suppression is a key step towards developing conservation biological control strategies. While numerous previous studies have demonstrated that diverse predator assemblages can be more effective in controlling pest populations, others have shown that it is the presence or absence of competitively superior species that is critical to pest biological control (i.e. selection effect). The present study investigated how increasing ground beetle body size diversity increases prey suppression. A mesocosm experiment was conducted to compare invertebrate prey suppression between nine created ground beetle assemblages. Size diversity of these assemblages was manipulated according to three diversity levels: low, medium, and high diversity. Partitioning of the diversity effects revealed that increasing the ground beetle size diversity had no effect on the strength of prey suppression. The absence of an effect of ground beetle size diversity may be because of the absence of resource partitioning among different-sized ground beetles. The amount and range of prey consumed increased with increasing ground beetle body size. Thus, prey suppression was strongly strengthened by the presence of large ground beetles in the assemblages. The present results suggest that for biological pest control, Agri-managers should emphasise practices that promote the presence of large carabids. This is not only because promoting the presence of large carabids could be at least as effective as conserving a diverse ground beetle community, but also because large ground beetles are more vulnerable to environmental disturbances and to predation than ground beetles of the other size classes.