Spatiotemporal scales of non-equilibrium community dynamics: A methodological challenge

The Intermediate Disturbance Hypothesis [IDH] and the Gradual Climate Change Hypothesis [GCC] offer intuitively appealing, verbal non-equilibrium explanations to species coexistence in competitive communities, but so far they lack a solid theoretical background and a proper experimental methodology. To make them testable and comparable on a solid methodological basis, they should be formulated as well-defined non- equilibrium community dynamical models. We suggest that this is possible, if explicit assumptions on the spatiotemporal structure of the environment and the pattern-generating mechanisms of the species assemblage in question are given. In the framework of a non-spatial population dynamical model we show that disturbance and climate change effects can be safely distinguished, and the "intermediate" level of external effects leading to maximum community diversity can be quantified. Based on the information statistical analysis of field data and simulation results, we explain why it is necessary to consider simultaneously the spatiotemporal patterns of the vegetation, the abiotic environment and the disturbances in order to predict the consequences of external effects regarding community diversity.