Alladi Ramakrishnan Hall

Investigation of bistability in ecosystems using cellular automaton lattice models

Kushal Appilineni

Indian Institute of Science, Bengaluru

Ecosystem regime shifts can often be abrupt and irreversible, occurring in response to small or gradual changes in environmental conditions. Several simulation and analytical models capture these discontinuous changes for a variety of ecosystems, ranging from inter-tidal mussel beds to semi-arid vegetation. Typically, strong positive feedbacks between organisms are considered a necessary condition for the occurrence of discontinuous state transitions. However, these models are complex, consisting of numerous parameters and detailed biotic and abiotic interactions, making it difficult to disentangle processes that cause abrupt transitions. In our study, we analyse a simple spatial model from non-equilibrium statistical physics consisting of only two parameters - one that controls environmental conditions affecting birth-death processes in the system and another that controls facilitation strength. By constructing and expanding the Master-Equation of this model and analysing the resultant Fokker-Plank equation, we demonstrate that demographic noise can promote bistability even in systems with weak positive interactions.