Analysis of ecosystem structure and function: extended path and flow analysis of a steady-state oyster reef model

An analysis of the extended path and flow structure of a six compartment steady-state oyster reef model was conducted. The extended path and flow structure were analyzed in the context of a refined canonical path classification system based on the systems theory methods of environ and network unfolding analyses. A computer implementation of an operational path classification system facilitated investigation of a finite portion (path length ≤17 arcs) of the direct and indirect path structure of the oyster reef model. Important results of the path structure analysis include: (1) few simple paths and large numbers of compound paths enumerated; (2) dominance of path numbers by subsequent passage terminal cycle paths; (3) structural evidence in support of feedback control in ecosystems; (4) results provide evidence by analogy to support the hypothesis of network homogenization first described using the systems analysis methods of environ analysis and network unfolding; (5) constancy of the pattern of origin–destination path counts with increasing path length; (6) importance of nonliving compartments in the extended path structure of ecosystems. Simultaneous path and flow analysis of the oyster reef model assessed the flow contributions of the fundamental path categories for this model using a modification of a path-based network unfolding method. First passage paths contribute most of the flow; however, multiple passage cyclic paths also provide a large (22%) flow contribution. Because of cycling in the system, the numerous long paths in the extended path structure of this ecosystem model are significant in its function as represented by the flows. These results provide microscopic evidence for the macroscopic results of environ analysis that implicate cycling as a key ecosystem attribute in the mechanisms of holistic system determination. The principles enunciated here for a model with a low cycling index (11%) carry over to, and would be even more significant for, models with high cycling indexes. These results also serve to form a link between the extended structure of food webs and their functioning as represented by energy-matter flows. The present analysis demonstrates that extended path structure, and the component articulation from which it is generated, have significant consequences for ecosystem function.