A qualitative model suggests that the soil ecosystem is resilient to the invasion by the land flatworm Obama nungara

Abstract Soil plays a critical role in ecosystem functioning and on the provision of ecosystem services. The soil fauna, especially earthworms, contributes to these processes through their action on the physical, chemical and biological properties of the soil. Recently, however, several regions of the world have been invaded by alien land flatworms, among which some species are predators of earthworms, but also of gastropods. In particular, Obama nungara , a flatworm originating from South America, has been abundantly introduced in Western Europe. In order to test whether and how the community of soil organisms can be maintained after O. nungara is introduced, we employed the Ecological Discrete-Event Network (EDEN) modelling framework to model all the possible trajectories that the community could take in an invaded garden. For this purpose, we focused on a reduced set of variables and formal rules describing the trophic chain exposed to O. nungara under two contrasting precipitation regimes. We demonstrated that the soil community is resilient to the invasion by O. nungara , since all losses of prey populations were reversible, except if the ecosystem was durably trapped in a situation of drought. Even in this case, endogeic earthworms could be maintained thanks to their limited reliance on the soil surface. We showed in this study the potential of possibilistic and qualitative models to conduct prospective studies on the impacts of invasive species on soil ecosystems, which can be more generally applied to a whole range of alien species and ecosystem types.