PS 32-203 - A non-consumptive effect mediates multi-predator interactions in coffee pest control

Abstract: Recent ecological research has focused on the role of higher-order interactions, such as non-consumptive effects, in the structure and dynamics of ecological communities. While the general ecological impact of these interactions is still being explored, less work has addressed their role in pest control, which is typically considered a consumptive process. In particular, non-consumptive effects in pest control may be crucial for mediating multi-predator interactions and potentially stabilizing pest dynamics.

Here we model the non-consumptive impact of a dominant ant species on a major coffee pest. We include two species of ants, Azteca sericeasur, which dominates coffee plants, and a ground foraging ant. The pest is the coffee berry borer, which exists in two spatially separated populations, on the plant, and in old berries that fall to the ground. Azteca consumes borers directly and throws them from the plant to the ground. Movement between the borer populations is modeled with downward and upward migration, and the non-consumptive effect of Azteca modifies the downward movement of borers. To test the impact of this non-consumptive effect on pest control, we ran simulations and systematically conducted parameter sweeps of the key model terms. All growth and consumptive interactions follow a standard Rosenzweig-MacArthur approach.

Initial results suggest that forced coupling of the two systems with downward migration results in large zones of chaotic dynamics. Fully coupling the system with upward migration eliminated the chaotic zones by synchronizing the two predator-prey systems. Importantly, when the non-consumptive effect term was increased in the fully coupled model, the mean densities and variability of both borer populations were reduced, indicating an increase in the efficiency and stability of pest control. While efforts to understand the mechanism behind this effect are ongoing, it may be that the non-consumptive effect works as a kind of predator density dependence, where the Azteca population is self-regulated by reducing its own resource supply as it grows.

Overall, these findings agree with previous laboratory results which show that multiple spatially separated predators can result in the best control of coffee berry borer when the non-consumptive effect of Azteca is involved. This effect may result in the lowest levels of damage on the focal coffee plant, but also may help to suppress the greater pest population by making borers more available to ground foraging consumers. This novel pest control mechanism should be further explored in assessing the dynamics of pest control in complex agroecological communities.