Use of a Trophic Structure Test Bed to Validate a New Systems-of-Systems Resilience Metric

Systems of Systems (SoS) combine complex systems such as financial, transportation, energy, and healthcare. A failure in a constituent system, however, can render the entire SoS ineffective by causing cascading faults. One method to prevent constituent faults from compromising SoS performance is to increase the SoS’s “resilience,” a measure of the SoS’s ability to cope with these faults and efficiently recover. Attempts to engineer improved resilience, however, are hampered by the lack of a metric to measure resilience across different SoS architectures (network arrangements). In a previous work, the System of System Resilience Metric (SoSRM) was presented as a possible solution, but the metric requires additional testing prior to being fully implemented as a SoS Engineering Tool. Validation of SoSRM is difficult because SoSRM itself was developed to bridge the gap of their not being a reliable metric to measure SoS resilience. Natural ecosystems are a type of SoS, where the products of one trophic level are used to feed organisms in a higher trophic level. If one trophic level faces a problem due to sudden change (e.g. a natural disaster), it affects members in the entire ecosystem, potentially causing ecosystem collapse. This work examines the key question:“ How can natural ecosystem characteristics be used to validate the SoSRM metric?” We hypothesize that analysis of a test bed of generic ecosystems then SoSRM values will positively correlate with biodiversity, providing a validation of SoSRM as a useful design metric. A review of current ecological literature reveals first principles for test bed creation including energy transfer rates, biomass ratios, number of trophic levels, and relationships between predator and prey. SoSRM is measured for 6 case studies in a biodiversity test bed. Results showed SoSRM scores correlated with expected ecosystem network structure (r² =.95, n=6), thus providing a validation of SoSRM as a design tool. Ecosystem network structure is quantified by applying graph theory to determine path length associated with each node. As a final check, 21 Ecological Network Analysis metrics previously derived from graph theory validate that SoSRM trends as expected with other elements of the System-of-System network structure (i.e. no correlation with number of nodes or links, positive correlation with robustness). By validating SoSRM, we provide a foundation for future work that focuses on increasing SoS resilience with biologically inspired design heuristics. This study is a key step to creating sustainable SoS that can resist the challenges limiting their utilization today.