Authors: Salgado-Rojas, José; Hermoso, Virgilio;Álvarez-Miranda, Eduardo;

Spatial connectivity is essential when planning effective conservation, especially for species that depend on different realms during their life cycle. Traditionally, most of efforts have focused on working on different realms independently, overlooking the propagation of threats across realms, the cumulative impacts of threats or tackled the problem using heuristic optimization models.
We present a mathematical programming model that identifies priority areas for the implementation of management actions for multiple threats across four realms (terrestrial, freshwater, estuary, and marine) to benefit multiple species simultaneously. We use the Tagus River (Iberian Peninsula) as a case study, where we integrate three different types of connectivity: longitudinal along rivers, and multidimensional in the estuary and marine realms. We simulate the propagation of threats across the study area using four types decay functions: two exponential decays (medium and high), one linear, and no decay. We then compare the allocation of management actions under two alternative scenarios: multi-realm planning vs single-realm planning. The results show that the multi-realm planning outperforms the single-realm, especially for species that depend on multiple realms and that the greater the propagation of threats, the larger the differences between scenarios. This model could help better address complex conservation management problems elsewhere.