| heal.abstract |
The role of indirect relations within an ecosystem is crucial to its function. Emergent properties such as adaptability, plasticity, and robustness are hard to explain without understanding the system-wide effects of direct and indirect interactions. In this paper, we take advantage of a different representation of ecosystem models to provide a better understanding of indirect effects. We focus on pathways of individual particles that flow through systems. Particles represent small units of flow material, such as a single carbon atom, 1 g of biomass, or 1 cal of energy. The view of an entire system from an individual particle perspective provides a more practical and intuitive basis to study indirect relations than earlier input-output based algebraic methods. Our findings show that the current two algebraic formulations for indirect and direct effect ratio (I/D) do not exactly compute their intended meaning. We come up with a new throughflow based I/D ratio, which revises the current definition, and accurately compares direct and indirect flows. The two different perspectives (algebraic and pathway-based) enable an insightful analysis and conceptual clarification as to what exactly each formulation measures. We compare all three measures on twenty real-life ecosystem models. Finally, we rescale the I/D ratio to I/(I + D) and define the later one as indirect effect index (IEI), which is better suited to compare indirect effects among different models. © 2012 Elsevier B.V. |
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