Waves of desertification in a competitive ecosystem

Abstract

We study a mathematical model inspired by a common scenario in northern Patagonia consisting of humans and their livestock living together with native wildlife. The main production system in this area is sheep farming, which due to wrong historical management has led to desertification of the habitat, with impact on both native wildlife and livestock. Particularly the largest native herbivore, the guanaco, has reflected in their numbers this alteration induced in the environment. We analyze a mathematical model that captures the main characteristics of the interaction between sheep and guanaco: the hierarchical competition and the advantage granted by humans to the herds, and also incorporates a dynamic for the habitat. Using the metapopulation formalism, the trophic web of two herbivores is extended over a patchy landscape that considers two characteristic times for the dynamics of the resource. Our study stresses the dependence of the metapopulations dynamics on the recovery time of the resource. These results are backed up by a deterministic mean field model which shares some similarities with the stochastic and spatially extended one. We find different regimes depending on the parameters considered: coexistence of both species, survival of a single species and extinction of the other, and extinction of both. Remarkably, in some regions of parameters space we detect the presence of periodical spatio-temporal patterns, with persistent oscillations of constant amplitude. Based on these results, we perform a characterization of the observed scenarios in order to gain insight about the system.