Autonomous biological control achieved through the coupling of two unstable control agents

Background/Question/Methods

One often-espoused goal of farm management is to achieve a level of self-sufficiency such that expensive off-farm inputs can be minimized. The conservation of biological complexity within agro-ecosystems may help achieve this goal through what is now known as autonomous biological control. Under this framework, the goal is not to eliminate pests completely, but to maintain permanent yet small populations of pests (below levels that would cause economic loss) that are controlled by permanent and diverse populations of natural enemies. Early experience with biological control was hampered significantly by the inherent instability of many of the control agents, suggesting that pursuit of the autonomous strategy could be difficult. Here, we test whether autonomous biological control can arise from the complexity of combining two separately unstable natural-enemy-pest pairings using hybrid Lotka-Volterra, S-I predator-pathogen-prey models.

Results/Conclusions

Our results show that combining two unstable two-dimensional systems (pest-predator and pest-pathogen) produces a stable three-dimensional system (pest, predator, and pathogen) that is robust to perturbations in initial conditions. Despite the imposition of direct and indirect negative interactions between natural enemies, the three dimensional system retains control over the pest population such that no outbreaks occur. Complex chaotic behaviors arise from the clash of predator-dominant and pathogen-dominant attractors acting as alternate stable states with evidence of hysteresis. These results give hope for an autonomous strategy of biological control that is maintained solely from the complexity of the agro-ecosystem rather than the addition of expensive, external inputs.