WHEN 2 AND 2 MAKE 4 - A STRUCTURED POPULATION WITHOUT CHAOS

Because a large number of theoretical models suggest chaos in populati ons, held biologists have been trying for decades to confirm the exist ence of chaos in nature. In spite of their efforts, chaotically evolvi ng populations have been found in extremely low numbers. In this artic le we consider a metapopulation model which was built up by the intera ction of local populations. Local populations interact with their near est neighbours via migrations, but migration occurs only if the local population density exceeds a threshold level (overcrowding). Depending on the strength of the interaction, the metapopulation density shows noiselike dynamics of many degrees of freedom, periodical evolution, o r tends to a fixed point. Low dimensional collective chaos has not bee n detected. Moreover, the migration size distribution indicates the em ergence of self-organized criticality, if the interaction is strong en ough.