Resilience, Indirect Effects and Cycling in Ecological Networks

Indirect effects index (IEI) and cycling index (FCI) are two key measures of ecological network analysis that are known to be correlated. Systems with high IEI values are assumed to be more stable and resilient. While this makes sense from a theoretical point of view, there is lack of evidence on the contribution of indirect interactions to ecosystem stability and resilience. Investigation of this relationship between resilience and indirect effects leads to a better understanding of IEI, that it is actually a sum of three distinct components (IEI-cycle, IEI-mixed and IEI-pure), each of which is identified by their relation to cycling. IEI and FCI are highly correlated because both values increase with average path length path, which is the average number of compartments a unit flow material passes through before exiting the system. While IEI and FCI are highly correlated, the third component of IEI, IEI-pure, is totally uncorrelated with cycling.This is because the effects of cycling are excluded from IEI-pure, by definition. Interestingly, we find out that IEI-pure is the major contributor to ecosystem resilience.