Construction of simple pathways and simple cycles in ecosystems.

We present software tools for overcoming the problem of combinatorics in the enumeration of simple pathways and simple cycles in a first flow-through analysis of carbon transfer in large ecosystems. Rather than search through the very large number of potential routes in a reasonably sized ecosystem for the relatively small number of actual routes, our main algorithm performs an efficient rule-based construction of the actual routes. The enumeration of the unique pathways becomes tractable in terms of CPU time, which increases linearly with ecosystem size and connectedness.

Stability patterns and trophic structure in a Delaware Bay plankton community.

Using qualitative loop analysis we have extended our examination of a Delaware Bay plankton community to include an investigation of the roles played by the various entities (population, guild or nutrient) in the community. In an entity removal exercise, we used stability relationships as a probe into community structure. Six types of stability change are possible as a result of entity removal from the system: stable to stable (s-->s); stable to unstable (s-->u); stable to disconnected (s-->d); unstable to stable (u-->s); unstable to unstable (u-->u); unstable to disconnected (u-->d).

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.

The potential for community level evaluations based on loop analysis.

In this paper we present results obtained with a computer simulation in which a community, described by Levins in his presentation of loop analysis (Levins, R., 1975, Evolution in communities near equilibrium, in: Ecology and Evolution of Communities, M.L.