(e.g., competition) is much smaller than the migration scale [@bierregaard2010losos].

In general, the dynamics of natural ecological communities is subject to substantial noise. Populations are exposed to environmental variations that affect their reproductive ability and death rate. This effect is, typically, quite strong [@tsimring2014noise; @lande2003stochastic]. Even under strictly fixed environmental conditions the stochasticity of the birth-death-migration process (demographic stochasticity) adds randomness to the dynamics. Under demographic noise, every finite population goes extinct eventually, so theories of community dynamics must include a stabilizing mechanism that makes these extinctions extremely rare (stable coexistence) or allow for a speciation process to maintain the species richness (unstable coexistence).

The mainland-island system incorporates features from both scenarios. On the one hand, in a local community there are at least a few extinction-prone low-abundance species. One the other hand, there are no absorbing states in the strict sense, as individuals of any species arrive at a fixed average rate from the mainland. Nevertheless, if the migration is relatively weak and the local population is not huge, some or perhaps all of the species may undergo temporary extinctions, leaving the island without this species until the next individual of this species arrives from the mainland and manages 