Network synergism: Emergence of positive relations in ecological systems

Traditional evolutionary theory depicts survival of the fittest as a difficult existence based on danger, conflict and strife. But, another view is emerging of a more synergistic organization in which ecosystems on the whole provide hospitable conditions for life. This world is populated by organisms mutually adapted and beneficial by virtue of their direct and indirect interactions. Many examples of mutualism have been explicitly observed (Bronstein, J.L., 1991. Bull. Ecol. Soc. Am. 72, 6–8; Cushman, J.H., Beattie, A.J., 1991. Trends Ecol. Evol. 6, 193–195; Casti, J.L., Karlqvist, A. (Eds.), 1995. Cooperation and Conflict in General Evolutionary Processes, Wiley, New York, 435 pp.), and we view mutualism as an implicit consequence of indirect interactions and ecosystem organization. This paper extends a methodology based on input-output analysis that models these synergistic relationships (Patten, B.C., 1991. Theoretical Studies of Ecosystems: The Network Perspective, pp. 288–351; Patten, B.C., 1992. Ecol. Modell. 62, 29–69). We show for simple storage-flow models that direct zero-sum resource transactions between organisms, when considered in context of the whole-system organization, produce integral (direct plus indirect) relationships more positive than the direct ones. This phenomenon, `network synergism', is demonstrated for two simple networks and a complete three component model. We also show, by looking at a limiting case, that system-wide synergism is ubiquitous, occurring in all models of any size or complexity. Network synergism emerges in these models because of three network properties: symmetry, indirectness and openness.