Complexity, system integration, and susceptibility to change: Biodiversity connection

Complexity of system organization involves hierarchy of structure. The hierarchy of structure emerges from the integration of components. Irrespective of the mode of system description, integration determines the hierarchy of the system and hence its effective complexity. Because hierarchy and integration are intrinsic features of ecological systems, they can serve to advance understanding of general properties of such systems. As hierarchical structure affects system assembly and repair, integration becomes a major determinant of such process. To demonstrate potential applications, I develop a quantitative model, grounded in the blind watchmaker analogy. This model shows that while hierarchical organization accords a substantial improvement in ability of a system to assemble or repair itself over a non-hierarchical assembly process, this improvement greatly depends on the interplay among three variables—the probability of perturbation, mean size of the subassembly, and the degree of integration. Specifically, high integration reduces time required to assemble (or repair) a system but it also demands higher levels of modularity (compartmentalization of interactions). In ecological terms, highly integrated systems should evolve towards increased specialization and compartmentalization (low direct connectivity), particularly in habitats where perturbation is locally infrequent.