Indirect effects and distributed control in ecosystems:

Comparative network environ analysis (NEA) is used to holistically explore controlling relationships in ecosystems. The term, distributed control, for the present series of papers, is adopted to describe a diffuse and decentralized concept of control residing in the complexity of organization. Starting with “open-loop” control theory parlance, three ecological control terms (control ratio, control difference, and system control) are derived in an environ framework by considering pair-wise and system-wide distributed control relationships. These control relationships are then explored using the seven compartment steady-state model of average nitrogen flow in the Neuse River Estuary, North Carolina, USA (Christian, R.R., Thomas, C.R., 2003. Network analysis of nitrogen inputs and cycling in the Neuse River Estuary, N.C., USA. Estuaries 26 (3), 815-828). Sediment and nitrates-nitrites (NOx) are shown to participate in opposing roles. If magnitude denotes dominance and therefore control, the control metrics reveal that sediment is overwhelmingly controlled by all components where NOx exhibits control over all components. However, if a limiting factor perspective is used (e.g., sediment sequestering N with a controlled release to NOx), the conclusions are opposite; sediment controls all other components and all other components control NOx. As such, the overall direction of the control relationship is the subject of further review. Thus far, the results are preliminary and this remains a throughflow based steady-state analysis with additional discrete time analyses planned.