Understanding Ecological Efficiency and Robustness for Network Design Using Thermodynamic Power Cycles

Ecology has acted as a source for sound design principles and studies of ecosystems have examined how ecological principles can enhance sustainable human network design. Engineered systems are often designed for maximum performance, but in many cases, robustness is lost due to unwanted variations in inputs or efficiency. Taguchi’s signal to noise ratio and other quality engineering principles are well known fundamentals in the field of robust design. In this paper, we will introduce flow-based metrics from ecological network analysis (ENA) for robustness, efficiency, and redundancy. Ecosystem robustness is related to the balance between flow path diversity and system delivery efficiency. Systems with diverse flows are more resilient to a disturbance since there are redundant pathways, but are inefficient because they contain many flow paths with the same endpoints. Efficient systems are better able to transfer material and energy, but this is at the cost of fewer pathways so the system is brittle. Thus to survive a disturbance, an ecosystem system balances redundancy with efficiency. Thermodynamic power cycles are used to understand the relationship between energy efficiency, measured using first law efficiency, and ecological robustness and an ecological balance of efficiency to redundancy (as measured by ascendency vs development capacity). The result highlights the importance of understanding differences in the meaning of efficiency between two fields, and that from an engineering standpoint robustness does not have to be sacrificed to obtain energy efficiency.