Shifts in ecosystem equilibria following trophic rewilding

Aim: Trophic rewilding is proposed as an approach to tackle biodiversity loss by restoring ecosystem dynamics through the reintroduction of keystone species. Currently, evidence on the ecological consequences of reintroduction programmes is sparse and difficult to generalize. To better understand the ecological consequences of trophic rewilding, we simulated the extinction and reintroduction of large-bodied mammals under different environmental conditions. Location: Europe. Methods: We selected four locations varying in productivity and seasonality in Europe and used a general ecosystem model called Madingley to run simulations. We initialized the model using body mass limits of a European Holocene baseline; we then removed large mammals and let the model converge to a new equilibrium. Next, we reintroduced the previously removed groups to assess whether the equilibrium would shift back to the initial condition. We tested three different reintroduction scenarios, in order to disentangle the importance of the different large mammal groups. Results: The removal of large-bodied mammals led to cascading effects, mainly resulting in increases in smaller-bodied herbivores and the release of mesopredators. Post-reintroduction, the system's new equilibrium state was closer to the initial equilibrium for stable and productive locations compared to highly seasonal and low-productive locations. The maximum trait space volume of the initial state and the post-reintro-duction state varied by 9.1% on average over all locations, with an average decrease in trait combinations of 6.6%. The body mass distribution differed by 28%, comparing the initial state to the post-reintroduction state. Main Conclusions: Our simulation results suggest that reintroducing locally extinct large-bodied mammals can broadly restore shifts in ecosystem structure, roughly resembling the baseline ecosystem conditions. However, the extent to which the ecosystem's state resembles the original ecosystem is largely dependent on the reintroduction strategy (only herbivores and omnivores vs. also carnivores) and timing, as well as local environmental conditions.