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.
A Nothofagus-dominated rainforest in eastern Fiordland, New Zealand, was sampled by shoot frequency in contiguous 1 x 1 m quadrats, along a topologically-circular transect. The data were analysed at five scales up to 5 x 1 m, to search for assembly rules, i.e., generalised restrictions on species co- occurrences. There was no evidence of niche limitation in terms of the whole community, at any scale examined. Rather, variance in species richness was greater than expected from a null model, suggesting environmental heterogeneity. This conclusion was confirmed by using a patch-model.