Dynamical effects of biocontrol on the ecosystem: Benefits or harm?

•Propose a three species model to explore dynamical benefits and harm of biocontrol.•Biocontrol can lead to very rich dynamics including varied types of bistability.•Biocontrol could be beneficial by promoting coexistence.•Biocontrol could be harmful by driving native species extinct.•Biocontrol can stabilize or destabilize the ecosystem depending on environments. Motivated by recent field studies on the effects of biocontrol beetle on invasive plants (Tamarix) on riparian ecosystems, we develop a simple three-species (the native consumer, the biocontrol agent, and their predator) model to explore potential dynamical benefits and harm of introducing a non-indigenous species into varied ecosystems with different habitat structures. Our proposed model assumes that (1) habitat consists of both native plants that are main food resources of the native consumer and invasive plants which are targeted food resources of the biocontrol agents; (2) the habitat structure is stable which has a fixed ratio of invasive plants; (3) biocontrol agents can defoliate invasive plants whose defoliations provide as additional food resources for the native consumer that could potentially increase the native consumer’s abundance; and (4) the predators feed on both the native consumer and the biocontrol agents. Our study shows that introducing biocontrol agents into the ecosystem can generate complicated dynamics that could be beneficial or harmful to the ecosystem depending on the environments: biocontrol agents could be beneficial by promoting its biodiversity such that all species could coexist; on the other hand, biocontrol agents could also be harmful by eliminating the native consumer or the predator. In addition, biocontrol agents could stabilize or destabilize the ecosystem depending on the habit structure and the local ecological environments. These theoretical results provide us potential decision-making tools that allow managers to better predict both safety and efficacy of candidate biological control agents are needed.