To examine the contribution of shifting gap mosaic to species coexistence, we analyzed a dynamical system composed of two regeneration stages (gap and non gap) and two species (tolerant and intolerant). Gap dynamics is described by disturbance rate (relative to recovery rate), assumed to be independent of species. Population growth is regulated by local density dependence upon per-capita fecundity and mortality. Produced seeds are randomly dispersed across gap-dynamic landscape.

A single species population achieves a unique equilibrium as far as its fecundity is larger than disturbance rate. It is necessary for coexistence that two species are different in mortality sensitivity to local crowding. Tolerant species needs to have higher carrying capacity than intolerant, though intolerant still needs to have higher fecundity than tolerant. Increasing disturbance rate brings about narrow range of coexistence. We also demonstrate that three-stage system allows the coexistence of three species.

The present model ignores the contribution of size structure in coexistence, which is separately examined by (gap-averaged) size-stratified model (Kohyama and Takada, in preparation). These two jointly cover the mechanisms suggested by the ‘forest architecture hypothesis’ (Kohyama 1993).