Stability-complexity relationships within models of natural systems

Drawing on the qualitative loop analysis models prepared by Lane for a Delaware Bay plankton community, we evaluated 12 systems that ranged from 14 to 18 entities (population, guild or nutrient). Our approach was to study models of extended trophic biotic communities and examine the stability-complexity issue not only as it exists between systems (the traditional approach) but also with respect to the entities and relationships within a given system. We found no statistically significant inverse relationship for stability and complexity between systems. Within a system, a significant inverse relationship at the entity level was observed embedded in an increasing stability positively related to increasing subsystem size. Also, within a system and from system to system, several entities were seen to vary their roles with respect to stability. These results extend the stability-complexity issue to models of relatively large biotic communities and raise issues concerning the roles, with respect to stability, played by entities within communities.