Predicting dynamic trajectories of a protected plant community under contrasting conservation regimes: Insights from data-based modelling

Data-based modelling of the dynamic behaviour of ecological communities is a big challenge in systems ecology and conservation biology. Implementing such models to forecast future scenarios is key for supporting decision-making in ecological reserves, given the multiple disturbances threatening their future. Using demographic and dynamic data for three tree (or tree-like) species from the Pedregal de San Ángel Ecological Reserve (Mexico City, Mexico), we constructed a family of dynamical models (using systems of ordinary differential equations) to reconstruct their dynamic interactions. The first two models considered two native species (Pittocaulon praecox and Buddleja cordata), with either antagonistic or cooperative interactions between them. These species have been considered ecosystem engineers playing different roles in the system and determining several community attributes. These models predict the transition from a stable steady state dominated by P. praecox (as reported in the 1950s) to the current community whose structure is apparently shifting to an alternative stable state dominated by B. cordata. The second pair of models additionally incorporate the invasive tree Eucalyptus camaldulensis, which exerts negative effects on all native plant species. The prediction of these models is an E. camaldulensis-dominated state with the exclusion of the native species from the reserve, provided this invasive species follows current population growth trends, without external intervention to check this process. Bifurcation analysis of this latter model allowed us to rationally design optimal intervention strategies that could potentially divert the trajectory from converging to an E. camaldulensis-only configuration into the stable coexistence of the native species. For the two-species and three-species models we made two versions, one with only competitive interactions and another one including a facilitation interaction between B. cordata and P. praecox. This analysis shows that facilitation is a requirement to achieve stable coexistence between the two native species, even in the presence of E. camaldulensis. The models constructed here, which integrate multiple data sources, help clarify conflicting empirical information regarding potential ecological mechanisms, and allow making predictions for strengthening the future management and E. camaldulensis control programs before its effects irreversibly modify the functioning and biodiversity of the biotic community protected in the reserve.