Many ecosystems exhibit striking patterns in the spatial distribution of organisms, for example, patterns of clumping and dispersion in semi-arid vegetation, mussel in inter-tidal beds and even sea-grass and macroalgae. Elucidating local-scale processes that generate these macroscopic patterns is of fundamental ecological importance. In addition, these patterns may provide early warning signals of impending regime shifts in these ecosystems. In our study, we investiate how facilitation drives commonly observed clustering patterns and affects the dynamics of semi-arid ecosystems.
Results/Conclusions
We use a spatially explicit model of ecosystem regime shifts, inspired by a simple model of state transitions in the physics literature. We reveal that a previously proposed early warning signal of regime shifts, the patch size distribution, is completely unrelated to ecosystem stability. It is driven by facilitative interactions in the landscape, and these interactions can be measured via the fractal geometry of patches. We demonstrate the theoretical results with vegetation data from semi-arid ecosystems also. We argue that a clear understanding of how local interactions between organisms scale to their spatial distribution is crucial to correctly inferring ecosystem stability.